This PDF file contains the front matter associated with SPIE Proceedings Volume 8549, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

The electron initiated avalanche gain and bandwidth are calculated for thin submicron GaAs n⁺-i-p⁺ avalanche photodiode. A model is used to estimate the avalanche build-up of carriers in the active multiplication layer considering the dead-space effect. In the model, the carriers are identified both by their energy and position in the multiplication region. The excess energy of the carriers above threshold is assumed to be equally distributed among the carriers generated after impact ionization. The gain versus bias and bandwidth versus gain characteristics of the device are also demonstrated for different active layer thicknesses of the APD.

A comprehensive charge control based analytical noise model for a symmetric tied gate 100nm gate-length In0.52Al0.48As/In0.53Ga0.47As DG-HEMT has been presented in this paper. The model evaluates the mean square drain noise current and gate noise current and the P, R & C noise coefficients for the device. The effect of the doping concentration and thickness of the donor-layer on the noise coefficients and hence on the overall noise performance of the device are also studied.

This paper presents a semi analytical technique for estimating the effects of intra-die process variations on the performances of an nMOS transistor. The intra-die process variability sources considered in the work are Random Discrete Dopants (RDD), Channel Length Variation (CLV), Oxide Thickness Variation (OTV) and Mobility Fluctuation (MF). The analog performances which are studied are transconductance g_m, intrinsic speed f_t , thermal noise spectral density S_n and flicker noise spectral density S_f. The estimation technique is based on BSIMIV-SPICE process parameters. The mean and standard deviation of the performance variations are estimated. The estimated results are verified through Monte Carlo (MC)-HSPICE simulation results.

This paper investigates the potential of ISESOV architecture for low-voltage digital applications. A circuit analysis is performed for ISESOV MOSFET in terms of voltage transfer curve (VTC), supply current and noise margin and switching speed. These results are also compared with the ISE, SOV and bulk MOSFET architectures. Further improvement in the characteristic of inverter in terms of VTC and noise margin is observed by incorporating the gate stack architecture. The impact of Dual Material Gate architecture on the inverter performance has been also studied through exhaustive device simulations and it can be concluded that. ISESOV is a promising candidate for future digital applications as compared to ISE, SOV and bulk because it combines the advantages of both ISE and SOV architectures.

An analytical model for a gate all around (GAA) Tunnel Field Effect Transistor (TFET) having circular and square cross section geometry has been proposed in this work describing the important device electrostatic parameters i.e. Surface Potential, Electric Field and Energy Band profile. Further, the model is extended for both a p-i-n and p-n-p-n architecture keeping in view the advantages offered by a p-n-p-n architecture (also known as tunnel source or halo doped TFET) over a p-i-n based TFET. The results obtained from the model have been validated with results obtained through Silvaco ATLAS 3D device simulation software.

This paper investigates the stress liner induced performance enhancement in multi-fingered devices. It is observed that the liner induced stress is not uniform in all the fingers and fingers located at the edges of multifingered devices have larger channel stress. As a result there is an unaccounted change in the drive current of fingers, sharing an active region, with the number of fingers in multi-fingered devices. It is observed that the average effective drive current in the fingers of seven fingered NMOSFET (PMOSFET) is ~4% (~17%) smaller than the single finger devices. We present a physically reasonable semi-empirical model relating average current and the number of fingers in a multi-fingered device. We show that using our model, one can predict the delay of an inverter with multi-fingered layout as a function of its number of device fingers.

The pnp SiGe HBT on thin film SOI is investigated with different Ge profiles using 2D numerical simulations in MEDICI. The base current, collector current, DC current gain, AC voltage gain, unity current gain frequency and breakdown voltage is obtained for a 0.09 × 1.0 μm² pnp SiGe HBT with triangular (0%-30%), trapezoidal (10%- 20%) and box (15%) Ge profiles in the base layer. The results obtained with the Ge profiles, has been analyzed and compared. The F_t BV_CEO product for triangular, trapezoidal and box Ge profiles has been found as 190.8, 401, and 359.6 GHzV respectively. The tradeoff between voltage gain and unity current gain frequency for the Ge profiles has been analyzed. The simulation result suggests that the pnp SiGe HBT on thin film SOI with trapezoidal Ge profile is a potential candidate for the high speed complementary bipolar circuits that can be used in high performance mixed signal applications.

With the rapid scaling down of the semiconductor process technology, the process variation aware circuit design has become essential today. Several statistical models have been proposed to deal with the process variation. We propose an accurate BSIM model for handling variability in 45nm CMOS technology. The MOSFET is designed to meet the specification of low standby power technology of International Technology Roadmap for Semiconductors (ITRS).The process parameters variation of annealing temperature, oxide thickness, halo dose and title angle of halo implant are considered for the model development. One parameter variation at a time is considered for developing the model. The model validation is done by performance matching with device simulation results and reported error is less than 10%.

Germanium has emerged as a potential contender to long-standing Si due largely to its augmented bulk carrier mobility, especially for holes. Nevertheless Ge MOSFETs suffer from poor interface properties and exhibit early onset of short channel effects (SCEs). Here we investigate how SCEs in Ge devices can be controlled by employing halo implants in presence of interface and fixed trap charge densities. Also halo implants are optimized to obtain a constant threshold voltage over a wide variation of channel lengths. In addition we study the effect of substrate bias in controlling short channel effects. Further the combined effects of halo concentration and substrate bias are investigated to attain a specified value of threshold voltage over a wide variation of channel lengths down to 50 nm. Results obtained from our model show excellent agreement with numerical simulation data obtained using ATLAS and also with reported experimental data.

Material parameters like ionization rate coefficients for electrons and holes play important role in determining the performance of IMPATT device. Accuracy of these material data is significant for the quality of simulation results. In this paper, the influence of small variation in the ionization rate data on the performance of 4H-SiC IMPATT diode has been presented using our computer simulation program.

In recent past extensive device simulation work has already been done on TFETs. Various ways have been suggested to model TFETs. In our paper we look at one such particular way to model these devices. The Non equilibrium green’s formalism has proved effective in modeling nano scale devices. We model complete SiGe and GaAs tunnel FET for the first time using the NEGF formalism, also taking acoustic phonon scattering into account. We analyze them on the grounds of I-V curve, I_on-I_off ration and subthreshold slope. The poisson equation and the equilibrium statistical mechanical equation has been solved by providing the potential profile.

In recent past extensive simulation work on Tunnel Field Effect Transistors (TFETs) has already been done. However this is limited to device performance analysis. Evaluation of circuit performance is a topic that is very little touched. This is due to the non availability of compact models of TFETs in the commercial simulator. We generate the TFET model by using the model editor in Cadence OrCAD V16.0. In this paper for the first time we perform the circuit analysis of Extended Channel Tunnel Field Effect Transistors (Extended Channel TFETs), we test them over basic digital circuit. Before that we perform device analysis of double gate extended channel TFETs, extended channel has been tried before on SOI TFETs, we try it for the first time on double gate Si _1-x Ge_x TFETs. We even look at the effect of introducing Si layer. The performance of this device is compared for different Ge mole fraction and also with MOSFETs.

Heterojunction solar cells have shown a promising comparable efficiency with the advantage of lower fabrication cost compared to the crystalline solar cells. In this paper, an attempt has been made to simulate the heterojunction structure and HIT structure using AMPS-1D software by applying various approaches. The simulation parameters of these structures are varied for cell efficiency, quantum efficiency, charge carrier concentration and temperature stability to achieve higher efficiency. The final solar cell parameters have been achieved about 20% for heterojunction and 23% for HIT cells. The effects on intrinsic and extrinsic characteristics of doped layers are discussed for these efficiencies.

Elemental and compound semiconductors, including wide band gap semiconductor SiC, are critically examined for high-power performance of IMPATT diodes at 94 GHz, in terms of efficiency, high-temperature operation and noise measure. Based on a new analysis applicable to a wide range of semiconducting materials and by using the available measured physical parameters, it is shown that wide band gap semiconductor, SiC, offer significant advantages compared to conventional Si and Ge for these applications. The new analysis uses peak electric field strength at avalanche breakdown, avalanche response time and noise-measure as critical material parameters for evaluating the quality of a semiconducting material for high-frequency, high-power operation of an IMPATT oscillator. The study show improvement by order of magnitude in the maximum breakdown electric field, four hundred fold improvement in the RF power output, and over all potential for successful operation beyond 600K for SiC W-band IMPATTs. The present study depicts the improvement in the efficiency by three orders of magnitude and avalanche response time by an order of amplitude of the IMPATT device, by replacing Si with SiC. The noise analysis shows that under similar operating condition, Si_0.5Ge_0.5 IMPATT is less noisy device than its counterparts. Though SiC IMPATTs outclass Si IMPATTs in terms of RF power, efficiency, noise level of these two types of IMPATTs are comparable (~ 17 dB).

Prospects of Si/Si_0.8Ge_0.2 heterojunction IMPATT devices are studied through a modified simulation technique and their performances are further compared with those of homojunction devices. This high-frequency study includes the effects of mobile space charge, parasitic resistance and also considered the detrimental role of elevated junction temperature on the maximum exploitable power level from the devices. The study indicates that under similar operating condition, Si/SiGe heterojunction IMPATT is capable of delivering a RF-power output of nearly 6W (efficiency 21%), two times higher than that from Si_0.8Ge_0.2 homojunction diode, which is only 13% efficient. The overall study indicates the superiority of the heterojunction diodes over their homojunction counterparts as far as negative resistance, device impedance and quality factor are concerned. To the best of author’s knowledge, this is the first report on highfrequency analysis of Si/Si_0.8Ge_0.2 heterojunction IMPATT.

Shielded-gate trench-MOSFETs yield superior performance compared to conventional gate trench devices by allowing higher doping density in the drift region and providing a ‘shielding effect’ for the gate by placing an intermediate electrode between gate and drain. However, further design optimizations can be done for a shieldedgate trench-MOSFET to improve performance parameters particularly suited for next-generation high-frequency computing power supply applications and they have been outlined in this article. Channel optimization, substrate thinning and intrinsic gate resistance reduction (by layout enhancements) have been discussed along with their impact on cost-performance benefit on the device. Further, effects of these design optimizations on the power loss and efficiency of a high-frequency switching converter have been demonstrated by mixed device–circuit simulations.

A model is developed to study SiC-based IMPATTs to operate at D-band frequency and the device properties of 3C, 4H, 6H-SiC based SDR IMPATTs are compared at the same operating conditions and frequency of operations. A noise analysis model is also developed to compare the noise characteristics of 3C, 4H and 6H SiC-based SDR IMPATTs. The results show that 3C-SiC based SDR IMPATTs have better power delivery capability whereas 4H SiC-based SDR IMPATTs are less noisy. When a power noise tradeoff consider, it is seen that 4H SiC-based SDR IMPATTs have better Noise Measure than the other two polytypes. These results can be used as the first hand information by the experimentalist.

We have investigated the total dose effects of 100 MeV Oxygen ion irradiation on the dc electrical characteristics of Silicon-Germanium Heterojunction Bipolar Transistors (SiGe HBTs). The results of oxygen ion irradiation were compared with Co-60 gamma irradiation in the same total dose range (1 Mrad to 100 Mrad). The results show that even after 100 Mrad of total dose, the degradation in the electrical characteristics of SiGe HBT is acceptable from the circuit design point of view.

The dc electrical characteristics of NPN RF power transistors were studied systematically before and after 175 MeV Ni¹³⁺ ion and Co-60 gamma irradiation in the dose range from 100 krad to 100 Mrad. The transistor parameters such as excess base current (ΔI_B= I_Bpost-I_Bpre), dc current gain (h_FE), and collector-saturation current (I_CSat) were studied. The base current (_IB) was found to increase significantly after irradiation and this in turn decreases the h_FE of the transistors. Further, the output characteristics of the irradiated devices exhibit the decrease in the collector current at the saturation region (I_CSat) with increase of radiation dose.

Cl₂/Ar based inductively coupled plasma etching of GaN/AlGaN is investigated using photoresist mask in a restricted domain of pressure < 10mTorr and RF power <100W, for selective mesa etching. The etch characteristics and rootmean- square surface roughness are studied as a function of process parameters viz. process pressure, Cl₂ percentage in total flow rate ratio, and RF bias at a constant ICP power, to achieve moderately high GaN etch rate with anisotropic profiles and smooth surface morphology. The etch rate and resultant rms roughness of etched surface increased with pressure mainly due to dominant reactant limited etch regime. The etch rate also increased with increasing Cl₂ % as a result of increased chlorine radicals that enhances chemical etching. The etch rate and rms roughness showed strong dependence on RF power with former increasing and later decreasing with applied RF power up to 80W. The process etch yield variation with applied RF bias is also reported. Negligible etch selectivity was observed between GaN and AlGaN up to 25% aluminum concentration with etch rate ~120nm/min. The studied etch parameters resulted in highly anisotropic mesa structures with Ga rich etched surface.

60 and 100 MeV Oxygen ion induced forward current gain degradation on 2N 3866 transistor is investigated by making I-V measurements before and after irradiation. It clearly shows that the decrease in gain in 60 MeV O-ion transistor is drastic, hence depicts that the device is vulnerable for low energy irradiation. The observed degradation is mainly due to total ionizing dose. The ionization leading to an increase in the total base current that eventually reduces the current gain. C-V measurements are made to estimate the effect of irradiation on the doping concentration of the devices. A plot of (1/C₂) versus voltage shows that the doping concentration of the basecollector junction of the transistor increases upon oxygen ion irradiation.

This paper explains the extraction of parameters of Angelov’s model for 0.25μm GaAs pHEMT (2x100μm) devices using extensive measurements without using any expensive extraction software. For DC parameters, we analyzed the equations associated with the parameters and established an effective extraction procedure. The small signal parameter extraction was also carried out extensively at various bias points and the bias dependency has been added for certain non-linear elements in the complete model. The model accuracy has been confirmed by I-V matching, S-parameter matching and single tone harmonic levels matching between the measured data and the modeled characteristics. The average percentage accuracy between modeled and measured data has been found out to be around 94-95% for Sparameter matching at different bias points and around 88-89% for I-V matching.

Amplification is one of the most basic and prevalent RF/Microwave circuit functions. This paper describes the design of an MIC(microwave integrated circuit) LNA(low noise amplifier) using PHEMT(Pseudomorphic High Electron Mobility Transistor) ATF-36077 in the frequency band 4.8 to 5.2 GHz The amplifier is designed using the Agilent’s ADS (Advanced Design System). The software was used to do minimum noise matching for the input stage and matching for maximum gain for the second stage. ADS has been used to design the input and output matching networks. A completed design of the amplifier was further optimized. The layout generated by the software was used to fabricate the amplifier. Momentum analysis of all the transmission lines and stubs used in the design was carried out to take into account the parasitic effects. Also, the method for the measurement of sub 1 dB noise figure is described for accurate measurement of noise figure. The LNA has demonstrated gain of 23.4 dB and noise figure 0.8-1.1 dB in the desired frequency band.

A recent report on realization/studies of Si-SiC hetero junction has given impetus to explore them for generation of rf power in double drift impact ionization avalanche transit time (IMPATT) mode. MM-wave properties of this hetero junction are compared with corresponding Si and SiC homo .junction. Interesting feature of ionization free n-SiC zone localizes the avalanche zone to less than 10% of depletion zone resulting in diode efficiency around 27% (against only 10-15% for both homo junctions Si and SiC) and three fold high rf negative resistance, which can be therefore termed as promising high rf power source.

Electron transport properties of the 2-dimensional electron gas (2DEG) in Al_0.3Ga_0.7 N/AlN/GaN High Electron Mobility Transistor (HEMT) grown on Fe doped GaN template was investigated (a) experimentally using temperature dependent Hall measurements and (b) theoretically by taking into consideration different electron scattering mechanisms like polar optical phonon, dislocation and interface roughness scattering etc. The HEMT structure exhibited very high electron mobilities ~1700 cm² /V s at room temperature and 13800 cm² /V s at 30 K with a 2DEG density of ~1.1E13/cm². From the comparison of theoretical and experimental data, it is shown that interface roughness scattering limits the mobility at low temperature where as the high temperature mobility is limited by Polar Optical phonon scattering.

In this work, we demonstrate best in class 120V Lateral Drain NMOS devices using 0.4um CMOS technology. These devices are fabricated with just 1 additional mask to the baseline CMOS process flow. 2D TCAD simulations were first carried out to identify the device with best breakdown voltage (BVdss) and specific on resistance (Rsp) combination. Then, a Design of Experiment (DOE) in layout was carried out around the best simulated device for different geometries (channel, Drain Extension and Field plate lengths). Rsp as low as 244 mohm-mm2 is achieved for a BVdss of 177V. This is more than 35% improvement over the best device reported in the industry so far [1]. Increasing channel length helps in improving the full bias stability of the device, albeit at the cost of Rsp. However, Rsp still remains lower than present industry state of the art.

A new heterostructure based on Al_xIn_1-xN/GaN high electron mobility transistor (HEMT) on SiC substrate has been proposed for high frequency, where it offers the best performance in comparison to other two heterostructures like on Al_xGa_1-xN/GaN and In_xGa_1-xN/GaN. We have investigated the effect of different higher output characteristics in comparison to conventional Al_xGa_1-xN/GaN and In_xGa_1-xN/GaN with the Al_xIn_1-xN/GaN heterostructure, where the drain current is maximum for Al_xIn_1-xN/GaN and Al_xGa_1-xN/GaN heterostructure HEMT respectively for the same barrier thickness and for the same gate source voltage.

This article reviews some of challenges that the Power MOSFET designers need to address to meet the ever growing market demand for reducing power consumption in battery-powered portable applications. The critical power MOSFET design parameters such as threshold voltage (Vth), drain-source breakdown voltage (BVdss), on-resistance (Rdson), package footprint, gate-drive voltage, and Figure of Merit (FOM) have been discussed. It has been highlighted that the scaling features and ultra-low on-resistance of the Trench Power MOSFETs can be advantageously utilized for powerloss management. The MOSFET design requirements in battery protection circuits and load switches have been presented. It has been emphasized that the Power MOSFET designers need to trade-off between on-resistance and maximum current capability in smaller footprint packages. The merits of Wafer Level Chip Scale Package (WLCSP) in achieving minimum foot print, ultra-low on-resistance, and improved thermal characteristics have been discussed.

In this paper, a novel SOI MESFET with triple-recessed source drain drift region is proposed and its DC and RF characteristics are investigated in detail. The results show that the breakdown voltage, output power density, and current gain improved significantly. So the proposed structure which has superior electrical performances can be used as a high speed and high power device.

Full-scale, non-linear large-signal model of IV-IV SiC Double-Drift IMPATT diode with general doping profile is derived. This model, for the first time, has been used to analyze large-signal characteristics of SiC-IMPATTs at 94 GHz of MM-wave window frequency. Under small-voltage modulation (~ 2%, i.e. small-signal condition) results are in good agreement with calculations done using a linearised small-signal model. The large-signal values of the diode’s negative conductance (5x10⁶ Sm^-2), susceptance (104.0 ×106 Sm^-2), breakdown voltage (207.6 V), and power generating efficiency (15%, RF power: 25.0 W at 94.0 GHz) are obtained at modulation amplitude ~ 50% of DC breakdown voltage, for a fixed average current density. The large-signal calculations exhibit power and efficiency saturation for large-signal (< 50%) voltage modulation and thereafter decrease gradually with further increasing voltage-modulation. This generalized large-signal formulation is applicable for all type of IMPATT structures with distributed and narrow avalanche zones. The simulation is made more realistic by incorporating the diffusion effects, space-chare effects and the realistic field and temperature dependent material parameters in SiC. The electric field snap-shots and the large-signal impedance and admittance of the diode with current excitation are expressed in closed loop form.

The Radio Frequency Power Amplifier lies at the heart of all modern day communication systems ranging from the cellular infrastructure market to broadcast, radar, medical, automotive and military to name a few. Transmission systems not only require substantial power at high frequencies, but they are also one of the most demanding of semiconductor applications on account of their requirements for efficiency and linearity, which inherently introduces a tradeoff during design. Three types of device technologies have been in typical use for RF power amplification: the VDMOS (at frequencies upto 1 GHz), the LDMOS (at frequencies upto 3.5 GHz), and more recently the Gallium Nitride HEMT, which extends the frequency range upto 5-7 GHz. As an emerging technology, GaN has huge potential, but its widespread use is still currently limited by the level of experience, absence of reliable device models and prices which are roughly (6-10 times that of silicon). This overview highlights the distinct features of the RF Power devices and touches upon the performance metrics of the above technologies (in silicon and GaN).

A moisture sensor was fabricated based on porous thin film of γ-Al₂O₃ formed between the parallel gold electrodes. The sensor works on capacitive technique. The sensing film was fabricated by dipcoating of aluminium hydroxide sol solution obtained from the sol-gel method. The porous structure of the film of γ-Al₂O₃ phase was obtained by sintering the film at 450 °C for 1 h. The electrical parameters of the sensor have been determined by Agilent 4294A impedance analyzer. The sensor so obtained is found to be sensitive in moisture range 100-600 ppmV. The response time of the sensor in ppmV range moisture is very low ~ 24 s and recovery time is ~ 37 s.

Metal oxides currently constitute the most investigated groups of gas sensors. Among various metal oxides, tin-oxide has emerged as one of the potential candidate due to high conductivity coupled with high sensitivity to both oxidizing and reducing gases. In this context, attempts are made to deposit thin film of tin-oxide doped with antimony by spray pyrolysis technique on glass substrate which were heated at 375°C. The concentration of antimony was increased from 0.01% to 1%. The films obtained were blackish in color. The XRD pattern shows characteristic tin-oxide peaks with tetragonal structure. The NO₂ gas sensing properties were investigated at 250°C, it showed maximum sensitivity for the SnO₂:Sb films with 1% Sb concentration.

Nano-crystalline materials having large surface to volume ratio are promising candidates for gas sensor application. In order to achieve this nano crystallinity ZnO thin film is deposited on the quartz substrate by Metal Organic Chemical Vapor Deposition (MOCVD) technique. Diethyl-zinc (DEZn) and tert-butanol (TBOH) are used as the zinc and oxygen precursors respectively. The film properties are analyzed by XRD, FESEM and UV-visible spectroscopy. X-ray diffraction (XRD) studies showed that the film is textured along (002) plane. The FESEM images reveal the nano-size of the particles. From the optical studies it is found that the film is transparent in nature and the band gap is 3.24 eV. The gas sensing characteristics of the grown film is investigated in presence of CO gas as a function of temperature and gas concentration. The sensing results show that MOCVD grown ZnO thin films can be used as attractive reducing gas sensors.

A ceramic mercuric iodide X-Ray sensor probe is developed from highly pure mercuric iodide. Probe has high mechanical and chemical stability. Photoconductivity and stability are studied and analysed. It is found that dark current shows a pure resistive variation with increase in bias voltage where as photocurrent shows a sigmoidal behavior. Annealing in air helps in reducing the polarization effect and improving the sensor properties. Adsorption of iodine is found to drastically reduce sensor performance. Annealed probe shows a repetitive trend in switching characteristics.

Wafer-level micro-encapsulation is an innovative, low-cost, wafer-level packaging method for encapsulating RF MEMS switches. This article presents an approach for design and processing steps related to encapsulation of individual RF components e.g. CPW, RF MEMS switches, in view of the variation in performance subsequent to packaging. Bottom contact vertical packaging is more prone to misalignment margin and easy to make connections. Cavity height of 30 µm is optimized for bottom contact vertical packaging.

We report the use of proton beam lithography as a convenient procedure consisting of minimum steps for micropatterning in polymer multilayers comprising of a metallic intermediate layer – a structure which can facilitate many application including vertical organic field effect transistors. We have used focused micro-beam of 2 MeV protons to pattern array of micro-holes in a 1 μm thick tri-layer film. A tri-layer film was prepared by spin coating 400 nm poly(methyl methacrylate) (PMMA) film on a glass substrate followed by thermal evaporation of 200 nm thick aluminium film and spin coating of a second PMMA layer of thickness 400 nm on the top. MeV protons suffer very little scattering inside the tri-layer film and pass through the tri-layer following almost straight path. Thus MeV proton beam causes molecular chain scissions in the top and the bottom PMMA layer in desired patterns in a single exposure which is not possible with other techniques such as e-beam lithography (EBL) or photolithography. By following a step by step development/etching of the three layers, we achieved an array of through micro-holes in the tri-layer film on the glass substrate. Potential application of such micro-patterns is discussed. We also report optimized parameters of proton beam writing for arrayed micro-structures fabrication in single layer of two different common polymer resists, SU-8 and PMMA. The surface morphology and side wall broadening of the fabricated structures were characterized using SEM and profilometer study respectively.

An optical MEMS (micro-electromechanical system) pressure sensor fabricated using bulk silicon micromachining techniques and tested using single wavelength interrogation technique is presented here. The sensor described here was designed for low pressure range applications. The operating principle of the sensor is Fabry-Perot (FP) interference. Experimental results demonstrate that the sensor has reasonable linearity, sensitivity, low hysteresis and a very good repeatability. Sensor’s response was found to be comparable with the theoretical predictions[3].

Biomedical and CMOS/MEMS hybrid systems are currently being engineered and investigated widely for food and water safety applications. There are many recent advances for pathogen detection in food and water. There are many opportunities and challenges to improve the current technology. In support to these efforts, in this work effect of Electric double layer, cell wall, alkalinity and temperature variation on the capacitance values that are important for an impedimetric sensor, has been analyzed. The results obtained with this model have been compared with the finite element solution using Comsol Multiphysics™.

In present work, we report the synthesis of SnO₂ nanowires on gold catalyzed silicon substrate and implementation of these grown SnO₂ nanowires as a sensing element for methanol sensing. The SnO₂ nanowires were synthesized by using thermal evaporation method. The growth of SnO₂ nanowires was carried out on gold catalyzed silicon (Au/Si) substrate by thermal evaporation of a mixture of SnO₂ and graphite powders in Argon (Ar) ambience at a temperature of 1050°C. The growth of SnO₂ nanowires takes place at atmospheric pressure. The surface morphology study reveals the growth of SnO₂ nanowires (diameter~ 300 nm, length~ 50 μm) on the Au coated silicon substrate. The XRD analysis concludes that synthesized SnO₂ nanostructures show polycrystalline nature with tetragonal rutile structure. The vapor-liquid-solid (VLS) growth mechanism of SnO₂ nanowires were also confirmed by EDX spectra. The SnO₂ nanowires were used to fabricate single SnO₂ nanowire based methanol gas sensor. The result reveals that the device exhibit the resistance change from 23 MΩ to 10 KΩ upon exposing to 200 ppm concentration of methanol gas at 100°C. This sensing behaviour offers a suitable application of the SnO₂ nanowire sensor for detection of methanol gas.

Paper reports a resistive type humidity sensing studies of ZnO-SnO₂ nanocomposite powder pellets prepared through solid-state reaction route. When exposed to humidity, resistance of pellets decreases with increase in relative humidity from 10 to 90%. Sensing element with 25 weight% of SnO₂ in ZnO shows best results with maximum sensitivity of 1.25 MΩ/%RH in 10- 90% relative humidity range. This sensing element manifests smallest crystallite size of 60 nm as measured from XRD and lowest grain size of 92 nm calculated from SEM micrograph. This sensing element manifests low hysteresis, less effect of ageing and good reproducibility. The response and recovery time of sensing element SZ-25 is found to be 92 and 480 seconds respectively.

Adaptive mirrors are used in modern adaptive optics systems for direct correction of aberration in a wave front. Silicon nitride membranes are widely used in the fabrication of MEMS deformable mirror In this paper, we have studied the design and simulation aspects of MEMS based electrostatically actuated continuous membrane adaptive mirror. We have studied the effect of several factors e.g. thickness and size of mirror membrane, size of bottom electrodes & voltage applied between top & bottom electrodes on response of the mirror.

Tunable gratings find applications in spectrometers, tunable cavity lasers and projection displays. In this paper, we discuss the design, modeling, fabrication process and optical characterization of a reflective type period tunable MEMS diffraction grating. The optical modeling of different grating periods for optimum efficiency is presented. A new fixed-fixed beam design with a uniform displacement over 33% of its length is proposed and simulated. The grating membranes are fabricated with gold metal. The optical characterization of the fabricated structure is presented.

The primary aim of the present work is to lower the operating temperature of the metal-oxide based sensors for detection of volatile organic compounds (VOCs) without compromising the sensitivity of the device. For this purpose, nanostructured oxides of ITO, Cu and Zn have been explored. The oxides of Cu and Zn have been synthesized by a novel process of thermal oxidation of the respective metal layers in air ambient without using any seed or catalyst layer. On the other hand, nanostructured ITO was obtained by RF magnetron sputtering process. For the heating of the sensing layer, a Ni microheater has been integrated on the sensor chip. Micro-electro-mechanical Systems (MEMS) technology has been adopted for the fabrication of the complete sensor for achieving the desired operating temperature at reduced power level. The sensor was extensively tested for a variety of VOCs such as acetone, methanol, ethanol and IPA. The issues involved in integrating nanostructured oxides with MEMS technology are also addressed.

The development of a simple, fast, disposable and low cost method for sensing and differentiating a wide range of concentration of toxic ammonia vapor by using colorimetric sensor is reported. A large dynamic range from 10 ppm to 1,00,000 ppm is successfully classified at ambient temperature with reproducible results. The CSA strip is consists of the dots of chemo-responsive materials, which are environmental friendly and react specifically with ammonia at different thresholds. The pattern of color change of colorimetric sensor array is unique for reported concentration range of ammonia gas.

The micromachined deformable or adaptive mirrors are being used in modern optical systems for astronomical imaging, laser-based communications and biomedical imaging. Deformable mirror fabricated using MEMS technology is a low cost, compact adaptive optical element for correction of the lower order optical aberrations such as defocus & astigmatism. In this paper, important development aspects of micromachined membrane mirror are discussed. The device has been successfully fabricated and characterized for various applications.

The paper presents the design and simulation of double spiral Pt-based microhotplate (MHP) for gas sensing application. A platinum resistor of 52 Ω has been designed and simulated on a 0.3 micron thick SiO₂ suspended membrane of size 40 × 40 μm2 using ANSYS. The SiO₂ membrane of size 40 × 40 μμm₂ and thickness 0.3 micron has been fabricated successfully by bulk micromachining in <100< orientation P-type silicon using 25% tetra methyl ammonium hydroxide (TMAH) solution. The simulated temperature and transit time response of microhotplate were obtained as 600.5 °C and 0.2 ms respectively at 4.8 mW power consumption.

The paper presents the design and mathematical model of a ZnO-based MEMS acoustic sensor. The structure consists with a 3.0 μm thick piezoelectric ZnO layer sandwiched between a pair of aluminum electrodes on a 30 μm thick silicon diaphragm. The size of silicon diaphragm is 3.1 x 3.1 mm². Resonance frequency of the structure is determined using harmonic analysis by ANSYS and found to be 41.8 KHz. Sensitivity of acoustic sensor with and without the effect of residual stress are obtained as 334.7μV/Pa and 221.6μV/Pa respectively. The proposed model of the acoustic sensor operated over a wide frequency range from 30 Hz to 8 kHz.

Being a II-VI semiconductor material with a wide direct band gap corresponding to the U-V region, ZnO finds important applications in U-V light sensors. In this work, we have developed and characterized Au-ZnO-ITO based UV photosensitive devices whose I-V characteristics show p+-i-n type behaviour and show an increased current under UV illumination. ZnO is employed as the active region. Both ZnO and gold were deposited via rf magnetron sputtering. The I-V characteristics of the fabricated UV sensor indicated a knee voltage of 0.69V. The resistance was observed to decrease by a factor of 3.5 under illumination. Further, we have optically characterized ZnO thin films deposited at different power levels to determine the dependency of various optical constants on deposition process parameters. These thin films were characterized using VASE (Variable Angle Spectroscopic Ellipsometer) and their optical properties including refractive index dispersion, band gap along with film thicknesses were extracted and modeled using WVASE modeling software.

This paper describes the design and simulation of RF MEMS SPST shunt and SPDT shunt-shunt switches with modified coplanar waveguide (CPW) configuration for X-band and Ku-band applications exhibiting high isolation and low insertion loss. By modifying the basic CPW structure for a six-strip membrane having length 720 μm, the resonant frequency can be reduced from 33.5 GHz to 13.5 GHz with isolation as high as -30 dB(-63 dB at resonant frequency) in Ku-band. Similar results are also found in case SPST and SPDT switches with other membrane types.

MEMS pressure sensors are one of the most widely commercialized microsensors in the MEMS industry. They have a plethora of applications in various fields including the automobile, space, biomedical, aviation and military sectors. One of the simplest and most efficient methods in MEMS pressure sensors for measuring pressure is to use the phenomenon of piezoresistance. The piezoresistive effect causes change in the resistance of certain doped materials when they are subjected to stress, as a result of energy band deformation. Piezoresistive pressure sensors consist of piezoresistors placed over a thin diaphragm which deflects under the action of the pressure to be measured. The result of this deflection causes the piezoresistors to change their resistance due to the stress experienced by them. The change is converted into electrical signals and measured in order to find the value of applied pressure. In this work, a high range (30 Bar) pressure sensor is designed based on the principle of piezoresistivity. The inaccuracies in the analytical models that are generally used to model the pressure sensor diaphragm have also been analysed. Thus, the Finite Element Method (FEM) is adopted to optimize the pressure sensor for parameters like sensitivity and linearity. This is achieved by choosing the proper shape of piezoresistor, thickness of diaphragm and the position of the piezoresistor on the pressure sensor diaphragm. For the square diaphragm, sensitivity of 5.18 mV/V/Bar and a linearity error of 0.02% are obtained. For the circular diaphragm, sensitivity of 3.69 mV/V/Bar and a linearity error of 0.011% are obtained.

This paper presents the simulation of various electromechanical performance parameters for an efficient and broadband air coupled Capacitive Micromachined Ultrasonic Transducer (CMUT) for Non Destructive Testing and Evaluation (NDT/NDE) using FEM simulation tool, Coventor Ware. The non contact ultrasonic inspection performed in ambient air reduces the complexity and cost. Various critical parameters like collapse voltage, resonant frequency, coupling coefficient, squeeze film damping, bandwidth, quality factor and transient response of the single cell of CMUT are discussed. We employ a hexagonal CMUT cell for the modeling to improve the CMUT’s transmission/reception efficiency as the average membrane displacement is high.

Electrectrochemical immunosensors have diverse applications in areas like medical diagnostics, food industry, environmental monitoring etc. The conductive materials like Indium Tin oxide coated glass (ITO), glassy carbon, porous silicon (PS) etc. can be useful as working electrode for electrochemical immunosensor applications. But the porous silicon is particularly attractive for this application due to its modified properties like very large surface area to volume ratio, surface dependent properties (electrical and optical), photoluminescence at room temperature and biocompatibility. In this paper porous silicon is investigated for development as working electrode for label free model immunosensor based on Human IgG.

The fundamental problem in the investigation of the properties of a quantum dot is the calculation of the energy eigen values of its confined charge carriers and evaluation of their corresponding wave functions. The quantum dots may be approximated as spheres whose surfaces constitute infinite potential barriers for carriers. Consequently, the motion of electrons and holes (which are confined inside the dot) can be analyzed by effective mass approximation applied to noninteracting particles. An attempt has been made here to solve the Schrödinger’s equation for particles inside the infinite spherical potential well to determine their allowed energy eigen values and eigen functions.

With a development and an increasing interest in flexible electronics, for civil, medical, space, and military domains, we present a design of a patch antenna using CNT-polymer ink on fabrics. We have prepared CNT ink, and measured its properties to use as a conducting material for making patches. The antenna is designed on cotton and Songket fabric that resonates at 2.3GHz on a 1.23 mm, and 1.06 mm thick fabric substrate with Εr ≈ 1.7, and Εr ≈ 1.9 for cotton and Songket respectively. Measured and simulation results shows that band width depends on thickness and type of fabrics we used. All antenna parameters such as VSWR, return loss, gain and radiation pattern meet the design criteria.

In this work, inelastic tunneling spectroscopy (IETS) of SiGe:C channel heterojunction PMOSFETs has been used to study the modes of vibrations (due to molecular species and phonons) present in the tunneling junctions and also to characterize the traps responsible for trapping/de-trapping of channel carriers. Peaks observed in the second derivative spectra of the drain-current provided information for identification of various traps and defects in the metal-insulatorsemiconductor (MIS) structures for thin tunneling oxide present in the SiGe:C PMOSFETs. Both the optical and acoustic phonons are observed for SiGe, SiO₂ and Si-C. From the spectra obtained by varying gate voltage between 180-350 mV (in both forward and reverse bias), the trapping/de-trapping process has been observed which comprises of charge trapping and trap-assisted conduction phenomena. The traps that take part in the trapping of carriers are also identified from the results.

This paper reports the formation and properties of hydrogenated amorphous carbon (a-C: H) films having embedded nanoparticles deposited by cathodic jet carbon arc (CJCA) technique in absence of magnetic field. The films have been characterized by XRD, HRTEM, XPS, dark conductivity, activation energy, optical band gap, residual stress, hardness, elastic modulus and plastic index parameter. The properties evaluated of a-C: H films having embedded particles have been compared with that of undoped and nitrogen doped a-C films having embedded nanoparticles deposited by CJCA technique. All the properties of a- C films studied are found to depend on the gaseous environment used during the deposition of the films. These a-C films having embedded nanoparticles act as hard coating materials.

An analytical potential model for threshold voltage of asymmetric Double Gate MOSFET (DG MOSFET) is derived by considering mobile charges. A cubiod function approximation is made for potential distribution of analytical solution of 2-D Poisson's equation. Different gate work functions are considered for both tied and independent DG MOSFET.The threshold voltage behavior of DG MOSFET for different body and oxide thicknesses is investigated. The analytical solution of threshold voltage is verified through TCAD simulation and is compared with existing threshold voltage model reported without consideration of mobile charges. The model developed considering the mobile charges, agree satisfactorily with other theoretical predictions.

Graphene, 2D form of graphite, exhibits excellent electrical conductivity and many peculiar properties^1-3. That’s why extensive research is going on this field worldwide. Here, we present the physico-chemical method for the synthesis of graphene sheets. Transmission electron microscopy (TEM) and Raman spectroscopy was used to characterize the graphene sheets and then graphene field-effect transistor was fabricated with copper as a sourcedrain electrode.

We investigate the purification of as-prepared multi- wall carbon nanotubes (MWCNTs) by exposure to ultraviolet lamp (λ=185 nm). UV irradiation was conducted under ambient condition in a UV lamp chamber which had a layer of reflective aluminium foil inside to ensure the entire sample would have an even exposure to UV. Raman spectroscopy before and after UV exposure indicates the removal of non-nanotube material. The narrowing of D-band is consistent with highly purified nanotube which is seen in our results. Raman result shows that the ozone oxidation can remove the defect site of nanotubes. Intensity of G- and D*- band increases rapidly with increasing the oxidation time. Intensity ratio I_D*/I_D increases continually with increasing the ozone oxidation time which confirm the reduction of impurities from the MWCNTs.

Energy eigenvalues and density of states of carriers in a finite barrier triangular quantum wire embedded inside a rectangular quantum wire are numerically investigated using finite difference technique (FD-Q). Time-independent Schrödinger’s equation is solved with appropriate boundary conditions for computation of lowest three eigenstates. The wire is made of lower bandgap GaAs material surrounded by wider bandgap Al_xGa_1-xAs, and the analysis is carried out by taking into consideration of the conduction band discontinuity and effective mass mismatch at the boundaries. The eigenvalues and the density of states are plotted as function of wire dimension and mole fraction (x). The results are also compared with those obtained using rectangular quantum wire.

The most important aspect of fabrication of Carbon Nanotubes (CNTs) based devices/sensors is the selective and controlled positioning of CNTs, which is a challenging issue for the researchers now a days. Here, we have presented a simple and efficient methodology for positioning of CNTs using 16-MHA self-assembled monolayers (SAMs), written over the gold substrate using Dip-pen Nanowriting (DPN). The analysis of the obtained AFM images clearly shows significant height increment of nanopatterns, which corresponds to the attachment of carbonaceous material over the written nanopatterns. Carbon Nanotubes (CNTs), Dip-pen Nanowriting (DPN), 16-MHA, 1-ODT and Self-assembled Monolayer (SAM).

Nickel ferrites were synthesized in various compositions by employing sol gel technique at different sintering temperatures. The sintered ferrites were characterized by XRD and SEM for structural and morphological studies which confirm the formation of Nickel ferrite nano particles. Dielectric and ac conductivity studies were performed on nano Nickel ferrites of different stoichiometric ratio. The effect of grain size on the dielectric response and ac conductivity is discussed in this paper.

The diffusion contribution to thermopower, S_d, is studied for pure semiconducting graphene nanoribbons (GNRs). The electrons are assumed to be scattered by acoustic phonons and optical phonons via deformation potential couplings and edge roughness. Numerical calculations of S_d, as a function of linear carrier density are presented. The relative importance of the carrier scattering mechanisms operative and the effect of subbands on the behaviour of S_d in GNRs are studied.

Diffusion thermopower, S_d, in suspended graphene is investigated for 100 < T< 350 K. Electrons are assumed to be scattered by in-plane and out-of-plane acoustic phonons. Numerical results show that, temperature dependence of S_d, is almost linear for both out-of-plane phonons and in-plane phonons, dominant contribution being from out-of-plane phonons. Comparison with recent available experimental thermopower data [Xu et al arXiv: 1012. 2937v1, (condmat. mes-hall)] obtains a good fit for T< 170K. S_d calculated using Mott expression is found to overestimate the values. Carrier concentration dependence is also studied. Role and relative importance of the two scattering mechanisms is studied.

The absorption spectra of semiconductor quantum dots (QDs) are expected to be a series of δ-function-like discrete lines due to the nature of the density of states. In a realistic III–V QD system, the absorption spectra is the superimposition of the contribution from each individual dot and the overall behavior is modeled by considering a Gaussian size distribution. In this paper, we study and present the dependence of the Gaussian nature of the absorption spectra of In_XGa_1−XN/GaN QD systems on the dot size distribution. The dots were approximated as elongated rectangular boxes having finite potentials at the boundaries. The optical transitions and absorption spectra of In_XGa_1−XN/GaN QDs that have a square base and the variation of the height is Gaussian, are computed and analyzed

As a new candidate in the p-type TCOs group, CuBO₂ has been under research spotlight in very recent years. The present work describes a new cost effective sol-gel technique to synthesize the CuBO₂ nanopowders and structural properties of the same were examined by X-ray powder diffraction studies. The particle size and other morphological information were obtained from field emission scanning electron microscope and transmission electron microscope. The compositional analysis was performed using energy dispersive analysis of X-ray. The transmittance spectra and hence the band gap of the as-synthesized CuBO₂ nanopowder was obtained by a UV-visible near infrared spectrophotometer. The photoluminescence property of this material is reported here for the first time and the material showed efficient photoluminescence with the appearance of a broad peak at 370 nm. The broad band can be deconvoluted and the different peaks were assigned to band to band transition and electron transition in Cu+ ions under the excitation, i.e. 3d⁹4^s1–3d¹⁰.

Si nanobar field effect transistors (Si-NBFETs) have emerged as one of the potential candidates in the present era of nano-structured electronic devices. In the current work, the carrier transport in ballistic Si-NBFETs is modeled by constructing a relevant Hamitonian matrix, where the coupling of source and drain with the channel is incorporated by the corresponding self-energy matrices. The Hamiltonian is solved by non-equilibrium Green’s function formalism. The current-voltage characteristics for different width and thickness of the nanobar channel are investigated in detail. Comparative study on drive current and leakage current for various transverse dimensions suggests a cross-sectional design window with an aspect ratio in the range of 1.3-1.6 to be appropriate for superior performance.

The well-known technique of insulator surface charging is performed here with a tip of a cantilever. The feasibility to prepare a surface charge memory device is discussed. Since the charging of high resistive insulator surfaces can be performed approximately without power consumption and the surface charging is a promising method to build memory devices in integrated electronic circuits. To this aim the surface of silicon dioxide (SiO₂) is charged with the tip of an atomic force microscope (AFM) for different charging voltage, different charging time and different thickness of the sample in contact mode. Afterwards, the charged surface is inspected with the same tip operated in the Kelvin mode. With the Kelvin option of the AFM the surface potential and topography of the samples can be measured simultaneously. Furthermore, a time dependent spread and an exponential-like decay of the surface potential with a time constant of about 15 h are observed . Due to this long-term stability and the possibility to reverse the sign of the deposited charge by recharging in opposite direction it is thinkable to use the system as a surface charge memory device. Additionally, surface potential measurements are performed on aluminum dioxide (Al₂O₃) samples.

We report the growth of high quality Cu doped ZnO thin films by magnetron sputtering. Cu concentration has been varied over three orders of magnitude (0.01%–10%). Higher growth temperature ensures high level of Cu doping. The XPS measurements revealed that most of the Cu atoms have substituted into the ZnO lattice sites. Room temperature ferromagnetism, with magnetic moment initially increasing and then decreasing with Cu content, has been observed in the thin film. Oxygen vacancy and dopant activation play crucial role in the observed ferromagnetism.

Device characteristics for long-channel Ge-pMOSFETs with different channel-orientations and figures of merit for analog applications are reported. The electrical characteristics include the capacitance-voltage curve at frequency 500 kHz and the transfer characteristics for both the low and high drain voltages. Various device parameters of Ge pMOSFETs have been extracted utilizing the measured data for both the regular i. e., Ge <110< and oriented i. e., Ge <100< devices with post metallization anneal. The oriented device exhibits augmented transconductance, while output resistance and intrinsic gain show improvement for the regular device. The conductance efficiency is almost same for both the regular and oriented devices in the strong inversion region of operation whereas the parameter exhibits some improvement for regular devices in the weak inversion region.

A visible blind photo detector based on ambient condition synthesized single crystalline ZnO nanospikes array over glass substrate is reported. The fabricated detector in a planner configuration exhibits exceptionally high UV to visible rejection ratio~3000 and considerably high ON/OFF ratio~270. Modulation of resistivity owing to adsorption/desorption of oxygen over the accessible high surface area of the spikes array in the OFF/ON condition remains behind the observed high photo-response

High pressure oxidation of SiC in nitric acid vapor with two different gas ambients at two different temperatures has been studied. The oxide growth rate is greater than 20 nm/hr at 500°C. Leakage current density of 10nm thick oxide grown in nitrogen ambient at 500°C is much lower than that of the oxide grown in oxygen ambient with the same thickness. The field strength of the oxide grown in nitrogen ambient is also significantly higher (7.5 MV/cm) thanthat of oxide grown in oxygen (3.7 MV/cm). Not only the oxidation rate is higher in N₂+HNO₃ ambient, but the resulting oxide also shows excellent electrical and reliability characteristics at 500°C. In contrast to 500°C, the oxidation rate is lower in N₂+HNO₃ ambient than in O₂+HNO₃ ambient at 450°C. However, the leakage current density of 3.8 nm oxide grown in N₂ ambient is two orders lesser than that of the oxide grown in O₂ ambient of same thickness. The quality of oxide grown in nitrogen ambient is better than that grown in oxygen ambient at both temperatures.

Band to band tunneling in semiconductors fundamentally depends of the complex bandstructure of the semiconductor within its bandgap. In this work, the orientation dependent complex bandstructure of InSb, InAs, GaSb, InP and GaAs, and the orientation dependent probability of band to band tunneling in these materials have been computed using an sp³d⁵s^∗ tight binding model. These direct bandgap III-V materials are attractive candidates for Tunnel FETs. Comparison of our results with Kane’s two-band model commonly used in TCAD simulation, demonstrates the inaccuracies of the latter. Our results will be useful in the design of better performing Tunnel FETs in these materials.

Ultra-thin HfO₂ high-k gate dielectric has been deposited directly on strained Si_0.81Ge_0.19 by atomic layer deposition (ALD). The effects of metal gate electrodes (Au, Pd and Pt) on dielectric properties and charge trapping behavior of metal-insulator-semiconductor (MIS) capacitors are investigated. Grazing incidence X-ray diffraction (GIXRD) analysis shows that the conversion from amorphous to crystalline phase start to appear in the HfO₂ films when annealed between 400-500°C. The measured ΔV_fband hysteresis in high frequency C-V characteristics are used to study the pre-existing traps in the dielectric. Low-frequency noise characteristics have been measured using MIS capacitors with contact area ~ 2×10^-3 cm². The power spectral densities (PSD) of the MIS capacitors with metal gate electrodes are compared and their bias dependencies are reported. While a two level random telegraph signal (RTS) is observed at low voltage, multilevel RTS is observed at higher bias voltages.

Ultrathin HfTaO_x gate dielectric has been deposited on Si_0.81Ge_0.19 by RF co-sputtering of HfO₂ and Ta2O₅ targets. X-ray photoelectron spectroscopic (XPS) analyses indicate an interfacial layer containing GeO_x, Hf silicate, SiO_x (layer of Hf- Si-Ge-O) formation during deposition of HfTaO_x. No evidence of Ta-silicate or Ta incorporation was found at the interface. X-ray diffraction (GIXRD) measurements show that as-deposited HfTaO_x films are amorphous; however, the crystallization temperature of HfTaO_x film is found to increase significantly after annealing beyond 500 °C (for 5 min) along with the incorporation of Ta (with 18% Ta). It has been found that HfTaO_x gate dielectric on Si_0.81Ge_0.19 exhibit excellent electrical properties with low interface state density (~6.0×1011 cm^-2eV^-1) and hysteresis voltage (<70 mV). Charge trapping/detrapping behavior of the gate stacks has been studied under constant voltage stressing and the degradation mechanism of the dielectrics has been studied in detail.

Two dimensional carbon nanostructures (carbon nanosheets) are fabricated using Hot Wire Chemical Vapor Deposition (HWCVD) technique assisted by H radical injection, using CH₄ as source gas. Carbon nanosheets are grown on crystalline Si(100) wafer as well as on corning glass substrate without using catalyst. The grown carbon nanosheets are aligned vertically on the substrate with thickness in the range of 10-20 nm and about 60-80 nm in height.

In this study, well-crystallized mesoporous anatase TiO₂ microspheres were synthesized by simple hydrothermal reaction. These spheres are submicrometer-sized (the diameter size of about 1 to 3 μm) and consist of packed nanocrystallites with diameters of ~5 to 9nm. The products were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and UV-vis spectrophotometer. The 3D TiO₂ microspheres exhibited significant photocatalytic degradation and photocatalytic activity was evaluated via the photocatalytic oxidation of Rhodamine B (RhB) in air at room temperature. The result also shows that mesoporous microspheres followed Langmuir-Hinshelwood (L-H) kinetic model.

Silicon nanowires were synthesized on silicon substrate by depositing Ag and Cu particles using electroless metal deposition (EMD) technique followed by HF/Fe(NO₃)₃ solution based etching at room temperature. Structural and optical characterizations were done on synthesized nanowires. Nanowires of diameter 45 nm to 200 nm having length 2 μm to 4 μm were evident from the scanning electron microscope (SEM) images with maximum aspect ratio 100. Optical absorption study using 400 nm to 1100 nm wavelength by UV/VIS spectrophotometer revealed that synthesized structures absorbed up to 78% of incident radiation in the wavelength range 400 nm to 820 nm, which is much better than that of bulk silicon as they absorbed maximum 67% of the radiation. This observation supports that the material synthesized could be a potential candidate for efficient photovoltaic solar cell and other optoelectronic devices.

Dislocations are native nanowires. The realization of well-defined dislocation networks allows the electrical characterization of only a small number of dislocations. Different types of dislocations were analyzed by integration into the channel of MOSFETs. A substantial increase of the drain current was proved if only a few dislocations are present in the channel of nMOSFETs. Low-temperature measurements indicate single-electron tunneling on dislocation core defects.

Experiments show that the layer of separate confinement heterostructure (SCH) has a significant influence on the emission spectrum of semiconductor optical amplifiers (SOAs). Reducing the thickness of SCH layer could improve the uniformity of carrier distribution among multiple quantum wells (MQWs). When the thickness of the SCH layer changes from 120 nm to 30 nm, the operation current for SOAs to exhibit the full-width at halfmaximum (FWHM) spectral width of above 270 nm could be reduced from 500 mA to 160 mA.

In this paper, the impact of varying the dielectric constant of the gate dielectric on the device performance of a double gate p-channel tunnel field-effect transistor (p-TFET) is reported for the first time. It is observed that fringing field arising out of a high−κ gate dielectric degrades the device performance of a p-TFET, which is in contrast with its nchannel counterpart, where the same been reported to yield better performance. Also, the impact of fringing field is found to be larger for a p-TFET with higher source doping.

This paper investigates suitable materials for tunnel FETs (TFETs). TFETs where entire body is made of group III-V and IV elements are simulated. In_1-xGa_xSb TFET with a mole fraction of x=0.75 shows a high I_ON/I_OFF ratio and steeper sub threshold swing. Finally, inverter, buffer, nand and nor gates are simulated using In_0.25Ga_0.75Sb TFET models and are compared with Silicon (Si) MOSFET gates in terms of delay, dynamic and leakage powers. InGaSb TFET gates have less leakage power compared to Si MOSFET gates.

Nanocrystalline ZnO thin films with different morphology were grown on silicon substrate by sol-gel process using different zinc acetate sol concentrations. These films were characterized by high resolution XRD, SEM, EDS, photoluminescence (PL) and UV-VIS spectroscopic techniques to reveal their structural, morphological and optical details. The blueshift in strong free excitons recombination peak is observed as the morphology of the film changes from spindle shape to nanorods to clustering of nanorods with increase in sol concentration due to quantum confinement effect in the nc-ZnO thin films.

One and two micron wide silicon fin patterns realized using standard g-line UV lithography are oxidized to accomplish nanowires. Simulation results envisage the possibility of silicon nanowire fabrication using top down fabrication approach. Experimental results show the feasibility of the process. SEM imaging was used to characterize the nanowires. Silicon nanowires up to 150 nm are demonstrated by the mentioned top down approach. Silicon consumption from three sides of the fins reduces their cross-sectional geometries. Stress developed during the oxidation of silicon leads to pinch-off in the fins, with aspect ratios <3. This pinch-off divides the fin patterns into two parts vertically; upper part detaches from the lower one and converges into silicon Nanowire, buried in silicon oxide. Simulation and process results for different process temperatures, time and fin aspect ratios are presented in the paper.

This paper reports the formation and optical properties of amorphous carbon film having embedded nanoparticles deposited by anodic jet carbon arc technique (AJCA). The films deposited have been characterized by x-ray diffraction (XRD), high resolution transmission electron microscope (HRTEM), and scanning electron microscope (SEM) and spectroscopy ellipsometry (SE) measurements. XRD pattern exhibits dominantly an amorphous nature of film. HRTEM investigation shows initially the amorphous structure. However, on closer examination nanoparticles were found to be embedded in the amorphous matrix. The effect of substrate bias and the magnetic field on the optical constants evaluated from SE have been studied. On comparison of deposition condition with and without magnetic field used in growing a-C films there is a change in the values of optical constants.

Studies were carried on the growth behavior of InN nanodots by plasma assisted molecular beam epitaxy on bare Si(100) substrates and their structural, optical, electrical properties. The growth was carried out by two different methods such as, (i) mono-step growth process at a low temperature and a (ii) bi-step growth process with the combination of low and high temperatures for the formation of single crystalline nanodots with well defined crystallographic facets due to cluster migration. Low temperature photoluminescence shows a free excitonic (FE) luminescence at 0.80 eV. The Raman spectroscopy and X-ray diffraction studies reveal that the nanodots as well as the film were of wurtzite structure and strain free.

A ZnO based thin film transistor (TFT) with bottom-gate configuration and SiO₂ as insulating layer has been fabricated and characterized. The ZnO thin film was prepared by spin coating the sol-gel solution on the p-type Si wafers. The optical and structural properties of ZnO films were investigated using UV measurements and scanning electron microscope (SEM). The result of UV-visible study confirms that the films have a good absorbance in UV region and relatively low absorbance in the visible region. The TFT exhibited an off-current of 2.5×10^-7 A. The values of field effect channel mobility and on/off current ratio extracted for the device, measured 11 cm²/V.s and ~10² respectively. The value of threshold voltage was found to be 1.3 V.

Thin films consisting TiO₂ nanoparticles were synthesized by a cost effective ultrasonic spray pyrolysis technique on Si(100) and glass substrates at temperatures of 350 and 450 °C. The films were found to be anatase phase of TiO₂ from GIXRD and Raman studies. Effect of substrate temperature on growth process was monitored using FESEM technique. The substrate temperature influenced the morphology of the films and also on the field emission properties. The asdeposited semi-conducting TiO₂ films were investigated for the utilization of alcohol sensor at room temperature.

Molecular electronics, in which a molecule having some nanometers of conjugation length is used as an active element, requires the ability to interface the molecule to macroscopic electronic circuits. For this application, the focused ion beam (FIB) is proposed out of various nano-scale patterning techniques because of its simplicity, minimum time and efforts needed for fabrication of large number of devices. We patterned I-pads with bridge thickness (<10μm) using photolithography and used FIB milling to fabricate contact electrodes separated by hundreds of nanometer. The approach was tested by device fabrication with pentacene deposition on patterned gold pads. We were able to successfully fabricate and demonstrate saturation in large number of organic thin film transistors with channel length in order of 200-300nm by this approach.

I study the magnetic susceptibilities in quantum wires of II-VI and IV-VI materials under a parallel magnetic field on the basis of a newly formulated electron dispersion law. It has been found taking quantum wires of nano compounds as an example that the mass and molar susceptibilities increase with decreasing film thickness and decreasing electron concentration respectively within the limit of quantum framework. I observe that the susceptibility ratio in both the cassese deviates from the well known 1/3 rd rule collectively with the fact that there is a critical zone within which the quenching of diamagnetic mass and molar susceptibility occurs.

This paper presents an analytical model for C-V characteristics of short gate-length GaAs MESFET under illuminated condition. The non-analytic Gaussian doping profile commonly considered for the channel doping of an ion-implanted GaAs MESFET has been replaced by an analytic Gaussian-like function for the simplicity of the present model. When the computed results of the proposed model are compared with numerical simulation data obtained by ATLAS™ device simulator, an encouraging correspondence between the two lends credibility to our model.

A ‘p-contact first’ process flow for InGaN/GaN LED with Al as n-contact and Ni/Au as p-contact resulted in high series resistance due to degradation in p-contact resistance during subsequent thermal processing steps. However, in order to adopt an ‘n-contact first’ process, it is necessary to develop a contact metallization scheme for n-GaN, which can withstand annealing in oxygen ambient, necessary for activation of p-contact. Al/Au, Ti/Al and Ti/Al/Au are studied as possible alternatives to Al for n-contact. It is found that Al/Au, Ti/Al and Ti/Al/Au contact results in lower contact resistance than Al alone contact. Thermal stability and immunity to oxidizing ambient for these contacts is studied by subjecting the samples to oxidizing ambient in the temperature range of 550 – 700 °C. While Ti/Al contact results in the lowest contact resistivity, it suffers from poor thermal stability. The contact resistance with Ti/Al/Au contact is comparable to Ti/Al. Ti/Al/Au also offers good thermal stability and immunity to oxidizing ambient. Thus use of Ti/Al/Au allows the use of ‘n-contact first’ process that is expected to improve the series resistance of the device and hence the efficiency of LEDs.

In this paper, the frequency response of a VLSI compatible Si-CMOS p-i-n photodetector suitable for high-speed, lowvoltage operation is studied. The model is developed considering the effects of diffusion of carriers from the substrate region and the parasitic elements due to the presence of multiple diodes in lateral configuration. The current density is calculated considering square-area photodetector. Results indicate the possibility of optimum designs to maximize 3dB bandwidth.

In this paper, we present a theoretical analysis of gated mode single photon avalanche detector (SPAD) that quantifies the contribution of different parameters to the single photon quantum efficiency (SPQE).The study gives the variation of SPQE of SPAD with dark count probability for different parameters such as pulse repetition rate, hold-off time, pulse width for constant photon intensity which reveals that there exists an optimum value of P_d for which SPQE is maximized.

The results of our analytical study on the formation of optical bands of III-Nitride Photonic Crystals are presented in this paper. The analysis is based on the propagation of Bloch waves through microstructured periodic dielectric materials, taking a model of 2D holey crystal of square lattice of GaN as example. Band gaps are opened up for both TE and TM modes in the square lattice for different d/a ratios, 'd' and 'a' being the diameter and lattice constant. The transmission bandwidth is seen to be wider for decreasing air -hole diameter irrespective of the polarization mode of the propagating light. Complete photonic gap may be found for material system of relatively higher contrast ratio.

Group III-V nitrides have become versatile semiconducting materials for short wavelength LEDs, high temperature transistors. The growth and device processing of these materials are significant due to unusually high bond energies of nitrides. Inspite of high dislocations densities in the order of 10⁹cm^-2 the optical and electronic devices based on nitrides show high performance compared to conventional semiconductor devices. Understanding of the behavior of dislocations in these materials structures are very important for the fabrication of devices. In the present study, GaN was grown on sapphire substrates using MOCVD. The dislocation density of GaN has been estimated by wet etching and HRXRD. The results have been correlated with the growth conditions. The dislocation density of the samples was found to be between 3.5x10⁹cm^-2 and 5.0x10⁸cm^-2.

AlGaN is a promising material to develop UVLEDs and HEMT devices due to the direct wide-band gap material. In the present investigation, AlxGa₁-xN alloys were grown on c-plane sapphire substrate by MOCVD. Al content x was varied in the composition range 0≤×≤0.6. The thickness and Al composition of the AlGaN was determined by HRXRD. The growth rate decreases on increasing the composition of Al. The critical thickness of pseudomorphic AlGaN layer decreases on increasing the composition. Thick layers resulted in cracks and it is important to grow thick layers with high aluminum content free from crack for deep UV LEDs.

In the present investigation, Al_xGa_1-xN/Al_yGa_1-yN/Al_xGa_1-xN double heterostructures have been grown on sapphire substrate using MOCVD. The active layer Al_0.18Ga_0.82N thickness has been changed as 14.8 nm and 23.4 nm by keeping the thickness of the Al_0.45Ga_0.55N barrier layer as constant. It has been found that full width halfmaxium (FWHM) of (002) undoped GaN without double heterostructures as 352 arc-secs where as for the double heterostructures it is found to be 523 and 483 arc-sec for the active layer thickness of 14.8nm and 23.4nm respectively. The photon decay time was found to be 125, 85 and 87 ps for undoped GaN, Al_0.18Ga_0.82N of thickness 14.8 nm and 23.4 nm respectively using Time Resolved Photoluminescence (TRPL).It has been observed that the well width has no effect on the radiative decay time which has been reported for the first time.

InGaAsP/InP Multi Quantum Well (MQW) based rib waveguide (WG) multi-wavelength PIN type photodiodes (PD) have been designed for Coarse Wavelength Division Multiplexing (CWDM) systems in which spatial bandgap tailoring have been accomplished by using post growth Fluorine (F) implanted QW Intermixing (QWI) as the integration mechanism. Two separate structures with different composition but same well widths are necessary to detect all CWDM wavelengths in which a In_0.5540Ga_0.4460As_0.9489P_0.0511/InP (15nm/15nm) MQW structure has a 14 channel coverage which spans from 1350-1610nm. The thicknesses of the i-MQW layer and different layers constituting the WG have been optimized to give a maximum efficiency of 22%. A carrier tunneling time of 20ps along with the transit time limited bandwidth of 86GHz gives a 3dB bandwidth of 43GHz by optimizing the i-MQW thickness and dopant concentration of the different layers of the waveguide. For all 18 channels insertion loss of 0.4-23dB has been obtained for a detection sensitivity of 21dB. Design issues related to the contact formation for extracting the photo-generated microwave power in such photodiodes have been presented along with few fabrication details of the integration process.

Zinc Oxide (ZnO) and indium doped ZnO (IZO) thin films with different indium compositions were grown on p-type boron doped Si substrates by pulsed laser deposition (PLD). The effect of indium concentration on the structural, optical and electrical properties of the film was studied. XRD, XPS and Raman studies confirm the single phase formation and successful doping of In in to ZnO. We observed various photoluminescence emissions, ranging from UV to visible, with the incorporation of In into ZnO. Room temperature Current-Voltage (I-V) characteristics showed good p-n junction properties for n-type-undoped and In doped ZnO with p-type substrates. The turn on voltage was observed to be decreasing with increase in In composition.

The transport properties of polymer blend have been investigated by using impedance spectroscopy (IS) and current density –voltage (J-V) measurements based on a single-layer structure of ITO/polymer/Al. Impedance spectroscopy measurements showed that the device can be simulated by an equivalent parallel R-C network with a contact resistance R_s in series, the resistance R decreases along with bias voltage. The variation of the whole conductance and capacitance of the device with frequency and bias can be understood by the carrier response and the transit time dependence on the bias in the polymer film.

The growth of nonpolar a- plane (1 1 -2 0) orientation of the GaN epilayers were confirmed by high resolution x-ray diffraction studies. An in-plane orientation relationship was found to be [0 0 0 1] GaN || [-1 1 0 1] sapphire and [-1 1 0 0] GaN || [1 1 -2 0] sapphire. SEM image shows the reasonably smooth surface. The photoluminescence spectrum shows near band emission (NBE) at 3.439 eV. The room temperature I-V characteristics of Au/a-GaN schottky diode performed. The Schottky barrier height (φ_b) and the ideality factor (η) for the Au/a-GaN schottky diode found to be 0.50 eV and 2.01 respectively.

SiC nanocrystals of size 4×30×40nm have been fabricated on Si (100)3° by a low cost spin-on technique in which Htermination produces smaller crystallites but larger crystallite density at the substrate surface steps. Low temperature photoluminescence and atomic force microscopy (AFM) confirms the formation of quantum dashes. It has been observed that the spin speed and H-termination plays a crucial role in the formation of quantized structures on Si.

We report the effect of Si, Cr, Sc doping in the crystalline structure, optical and discharge characteristics of MgO thin films. Silicon and multiple (Si, Cr, Sc) doped MgO thin films demonstrate higher secondary electron emission (SEE). Si doping with Cr and Sc doping in MgO films shows much higher SEE as compared to pure and only Si doped MgO films. The importance of optimum amount of Sc doping is seen in our study where SEE reduced with further increase in Sc doping. The structural attributes of MgO films are correlated to the observed changes in discharge characteristics in the context of varying amount of Si, Sc, and Cr doping.

In the present work we have used a two probe model, consisting of sandwiched molecules wires, of thiophene, between platinum electrodes, to study the mechanism of charge transport, temperaturedependence, atomic configuration of electrodes, molecule-electrode contacts, as well as effect of rotation of molecular wire on the conductance. We find that for short length the charge transport is explained by tunnelling, and with increase in molecular length it changes hopping phenomena; which in turn supported by modeling the conductance of molecular wire with change in temperature for the system. Thus the results shows highly length dependent and temperature invariant behaviour in the short wires and weakly length dependent and temperature variant behaviour in the longer molecular wires. The geometric symmetries for the thiophene molecule lead to the difference of the contact configurations between the molecule and the electrodes, resulting in different conductance.

White organic light emitting diodes were fabricated using two zinc complexes bis(2-(2-hydroxyphenyl)benzoxazolato) zinc(II) [Zn(HPB)₂] and bis(5,7-dimethyl-8-hydoxyquinolinato) zinc(II) [Zn(Me₂q)₂]. Zn(HPB)₂ emitted light in blue region while Zn(Me₂q)₂ emitted light in orange region of the visible spectrum. Hence, we achieved white light by combining the two complimentary colors of the materials and by optimizing their thickness as emissive layer. Commission Internationale de l'Eclairage coordinates of the device, with 35 nm thickness of Zn(HPB)₂ and 13 nm thickness of Zn(Me₂q)₂, were (0.28, 0.36) which were well within the white region. The device emitting white light showed maximum luminescence of 2582 cd/m² at 19 V.

We have fabricated organic complementary inverter comprised of p-channel copper phthalocyanine(CuPc) and n-channel hexadecafluoro phthalocyanine (F₁₆CuPc) based organic thin film transistors (OTFTs) with single Cu metal electrode for both type of OTFTs. The work function of Cu is nearly equal to the highest occupied molecular orbital (HOMO) of CuPc and lowest unoccupied molecular orbital (LUMO) of F₁₆CuPc hence it can be used as source/drain electrode for both type of OTFTs which shows field effect mobilities of CuPc and F₁₆CuPc based OTFTs are 1.27x10^-3cm²V^-1S^-1 and 3.30x10^-4cm²V- ¹S^-1 respectively. Voltage transfer characteristics of complementary inverter show high noise margins and switching voltage around V_DD/2 with a maximum gain in the order of 20.

Capacitance based spectroscopic techniques have been used to characterize defects in organic Schottky diode based on copper phthalocyanine. Traps have been created by varying the deposition flux. The high deposition flux induces the structural disorder evident from the broad and low intensity X-ray peak. These structural disorders give rise to the traps that clearly shows its signature in C-T characteristics. The step in temperature stimulated capacitance (TSCAP) measurements provides the information of trap level. It is shown that structural disorder is responsible for traps in CuPc thin films and controls the electrical characteristics of two and three terminal devices.

In this work, we demonstrate the effect of surface modification of as-synthesized oleylamine-capped spherical CdSe QDs of size (5-7 nm). The as-prepared CdSe QDs are highly luminescent, monodispersive and exhibit energy transfer effects upon their dispersion in MEH-PPV polymer matrix. However, repetitive washing of CdSe QDs upon suitable chemical treatment leads to enhancement in charge transfer process as observed in their corresponding MEH-PPV: CdSe nanocomposites. Here, no evidence of agglomeration effects and surface states were found. This enhancement in charge transfer is mainly due to the partial removal of oleylamine capping ligand, which acts as a hindrance in the interaction between polymer and CdSe QDs. The importance of this study is that as-synthesized CdSe QDs show effective energy transfer whereas after chemical treatment, it shows enhanced charge transfer mechanism which makes their corresponding nanocomposites useful for different applications in organic electronic devices such as efficient electroluminescent (OLED) and photovoltaic (OPV) devices respectively.

Semiconducting polymers have applications in many electronic devices such as organic light emitting diodes, organic solar cells, field effect transistors, memory devices, and many flexible electronic devices. In the organic electronic devices, metal-organic semiconductor interface plays a major role in determining the electrical transport. Earlier most of the studies were performed on electrochemically polymerized polypyrrole. In this study polypyrrole-poly(vinylidene) fluoride composite films synthesized by chemical oxidation method were used for contact fabrication in sandwiched geometry. Electrical transport measurements have been carried out in silver-polypyrrole-silver sandwich structure to understand conduction mechanism in the temperature range of 10-300K. It has been observed that Ag forms Ohmic contact with PPy and bulk controlled space charge limited conduction was the dominant current transport process in these sandwiched structures.

We report that the vacuum annealing of MgO films at 225°C results in the removal of water based contamination and the secondary electron emission coefficient increases from 0.09 to 0.15. The effective secondary electron emission yield increases from 0.2 to 0.75 at 200 mbar chamber pressure, as temperature increases to 250 °C. The effective secondary electron emission yield at 200, 350 and 800 mbar pressure shows similar trend during the heating as well as cooling of the MgO sample. Thermionic emission, smaller surface band bending and the removal of impurities at high temperature are possible reasons for the increase in secondary electrons of MgO thin films.

Printing technology is a low cost technique for the processing of organic electronic devices. Here, we report printing characteristics of poly (3,4-ethylenedioxythiophene) : poly (styrenesulfonate) (PEDOT:PSS), typically used as hole injection/transport layer in various organic devices e.g. organic light emitting diodes, solar cells, and field effect transistors. In this work, we optimize drop spacing and substrate temperature during ink-jet printing of PEDOT:PSS films on rigid (glass) and flexible (PET) substrates. Morphological characterization of the films was performed using optical and scanning electron microscopy. Optical transmittance was measured using UV-Vis spectrophotometer and sheet resistance of the films was measured using four-point probe technique. We find that substrate temperature and drop spacing significantly affect the morphology, in our case decreasing these lead to smooth morphology of the ink-jet printed PEDOT-PSS films.

Organic Light Emitting Diode (OLED) based displays are viable alternative to Liquid Crystal Display (LCD) displays. However, OLED displays are still costlier due to the low yield of production which is due to the visual defects in the displays. A defect-free display is a prime requisite for a flat panel display application. Hence it becomes important to understand the possible defects and their root causes. Here, we have created defects intentionally in a small OLED matrix and studied the possible visual manifestations in a Passive Matrix Light Emitting Diode (PMOLED) display by electrically probing and visualizing waveforms on a Cathode-Ray Oscilloscope (CRO).

Publisher’s Note: This paper, originally published on 10 October 2012, was replaced with a revised version on 22 July 2016. If you downloaded the original PDF, but are unable to access the revision, please contact SPIE Digital Library Customer Service for assistance. White polymer light emitting diodes (WPLEDs) are fabricated using poly(9,9-dioctylfluorene-2,7-diyl) (PFO) as host andpoly [2-methoxy-5-(2’-ethyl-hexyloxy)]-1,4-phenylene vinylene (MEH-PPV) as guest material having structure ITO(150nm)/PEDOT:PSS(40nm)/PFO:MEH-PPV(~ 68nm)/Ca(20nm)/Al(120nm). Photoluminescence spectra of blends with different MEH-PPV concentration reveal that at low doping level of MEH-PPV, blue emission from PFO and yellow emission from MEH-PPV co-exist due to incomplete energy transfer from PFO to MEH-PPV. Surface morphology of the spin coated blend films with different concentrations of MEH-PPV were studied using atomic force microscopy (AFM). It shows segregation/agglomeration of polymers at higher concentration of MEH-PPV (~8.0 wt %). Finally, WPLEDs, having MEH-PPV in the range of 2.0-8.0 wt%, were fabricated. We obtained best device at 2.0 wt% of MEH-PPV, it shows white light with Commission Internationale de l’Enclairage (CIE) coordinate of (0.30, 0.38). Electroluminescence turn-on voltage of the device was 4.0 V and maximum luminance reaches 1234 cd/m2 at 8.5 V. The luminous current and power efficiency at current density of 22 mA/cm2 were found to be 2.0 cd/A and 1.1 lm/W, respectively.

We calculate the short-circuit current density for an Al_xGa_1-xAs-GaAs multi-quantum well (MQW) solar cell by solving the rate equations and considering the effects of lifetime, escape time, capture time and transport time of carriers. The contributions from bulk and well regions of the cell are calculated separately. Short-circuit current density and efficiency are computed and plotted for different material and device parameters. Results indicate that the active layer thickness can be optimally chosen to obtain the maximum conversion efficiency keeping other parameters unchanged.

In this work, self bias variation, nitrogen introduction and oxygen plasma (OP) treatment approaches have been used for tailoring the band gap of hydrogenated amorphous carbon (a-C:H) thin films. The band gap of a-C:H and modified a- C:H films is varied in the range from 1.25 eV to 3.45 eV, which is found to be nearly equal to the full solar spectrum (1 eV- 3.5 eV). Hence, such a-C:H and modified a-C:H films are found to be potential candidate for the development of full spectrum solar cells. Besides this, computer aided simulation with considering variable band gap a-C:H and modified a- C:H films as window layer for amorphous silicon p-i-n solar cells is also performed by AFORS-HET software and maximum efficiency as ~14 % is realized. Since a-C:H is hard material, hence a-C:H and modified a-C:H films as window layer may avoid the use of additional hard and protective coating particularly in n-i-p configuration.

In order to upscale the production of thin film solar cells a cost effective and simple synthesis technique is required. Keeping this in mind we have investigated the effect of electrochemical deposition (ED) and inherently low thermal budget rapid thermal annealing (RTA) processing of CuInSe₂ in sulfur atmosphere. X-ray diffraction (θ-2θ) scans indicate increased grain size and improved crystallinity after RTA of ED films. Scanning electron microscopy images (SEM) suggest changes in surface morphology after sulfur incorporation. Raman spectroscopy results and temperature dependent conductivity measurements are also discussed in the paper.

Hydrogenated nanocrystalline silicon (nc-Si:H) thin films were deposited using very high frequency (VHF) plasma enhanced chemical vapor deposition (PECVD) technique at 60 MHz. Films were grown at different power from 5 W to 40 W. The maximum deposition rate was found to be 6.1 A⁰/sec at 20 W power. These films were characterized by XRD which revealed that the size of the Si nanocrystals are in the range of 15.7 to 19.6 A⁰. The optical band gap was found in the range between 1.64 to 1.74 eV.

Nanocrystalline cubic silicon carbide (nc-3C-SiC) films are deposited using hot wire chemical vapour deposition technique at ~350 °C on glass substrates using SiH₄ /CH₄/H₂ as precursor gases. We investigated the influence of total gas pressure on the structural, optical and transport properties of nc-3C-SiC films. Raman scattering spectra and X-ray diffraction patterns revealed that the film prepared below 2 mbar is nanocrustalline silicon (nc-Si), while at ≥ 2 mbar films are nc-3C-SiC. We achieved high deposition rate (≥ 14-20 nm/min), high optical band gap (3.2-3.4 eV) and high conductivity (~ 10^-4 -10^-2 Ω^-1cm^-1) suitable for window layer for Solar cells.

In our work, we demonstrate the use of Copper Indium Gallium Diselenide(CIGSe) nanocrystals as electron acceptor in conducting polymer POLY(3-HEXYLTHIOPHENE)(P3HT) AND POLY(P-PHENYLENE VINYLENE) (PPV). We study the photo-induced charge separation and photostability of CIGSe-conducting polymer nanocomposites for the application of solar cells. CIGSe with P3HT ensures efficient charge transfer process across polymer-CIGSe interface as evident from higher quenching of Photoluminescence(PL) emission and higher value of rates of PL decays(PL/PLi), Stern-Volmer quenching constant K_vs and number of accessible fluorophores( F_a), as compared to MEH-PPV polymer. P3HT polymer owing to its crystalline lamellar structure and ordered morphology impart stability to CIGSe composite. Hence superior morphology and photostability as compared to MEH-PPV:CIGSe nanocomposites. P3HT:CIGSe nanocomposites may be exploited as potential active layer in photovoltaic and photoelectrochemical devices.

Degradation of bulk heterojunction organic photovoltaics (OPV) based on poly (3-hexylthio-phene) (P3HT) and (6,6)- phenyl-C61- butyric acid methyl ester (PCBM) as photo-active material has been investigated. In this manuscript, we present the degradation studies on organic solar cells under different experimental conditions: (i) stored and encapsulated under ambient condition and (ii) stored in vacuum and encapsulated under nitrogen (N₂) atmosphere. The dark current density-voltage (J-V) characteristic of the diode is used to understand the mechanism of degradation.

Study of structural, electronic and optical properties of oxygen and Mn substituted ZnIn₂Te₄ are carried out by DFT based first principle calculation using TB-LMTO method. They are found to be direct band gap semiconductors with band gaps 0.68 eV and 1.3 eV respectively. We have made a comparative calculation of real and imaginary part of the dielectric functions of both ZnOIn₂Te₄ and ZnMnIn₂Te₄. We have also calculated the static refractive index for both the compounds. Refractive index and absorption co-efficients are plotted for both the systems for better understanding. We have found that the substitution of oxygen and Mn in ZnIn₂Te₄shift the major absorption peaks towards lower energy. Absorption peaks are maximum at energy 1.2 eV and 2.80 eV for ZnOIn₂Te₄ and ZnMnIn₂Te₄ respectively.

Use of selective emitters is an important step in increasing the efficiency of commercial crystalline Si solar cells, but costs must be kept under control. Laser doping allows selective doping of precisely defined regions without the need for process- and labor-intensive photolithography steps while maintaining or improving cell quality. Laser processing parameters must be investigated to optimize doping and minimize defect generation and contact resistance to realize optimal photovoltaic performance. Lasers are available in a wide range of wavelengths, pulse durations, fluences, and energy distributions. Processing parameters must be selected with both performance and industrial feasibility in mind.

The HfO₂/p-GaAs metal-oxide-semiconductor (MOS) structures have been fabricated by developing and simulating an optimized process recipe. The optical dielectric constants and refractive indices of atomic-layer-deposited (ALD) HfO₂ films and the GaAs substrate are extracted from spectroscopic ellipsometer (SE) measurements. The quality of interface and that of the ALD HfO₂ films is investigated by analyzing capacitance-voltage (C-V) and conductance-voltage (G-V) data. Simulations of C-V and G-V data have also been performed for a similar process recipe to comprehensively understand the electrical quality of the dielectric layer. The optical dielectric constants for HfO₂ and GaAs layers are obtained to be 4.5-3.6 and 10-25, respectively, while their refractive indices are obtained to be 2.12-1.89 and 3-5.2, respectively. A frequency dispersion of the C-V graphs is observed indicating the presence of a Ga₂O₃ interfacial layer which has been confirmed from the device simulation. A flat band voltage shift of − (0.68-1.05) eV and interface state density of (5×10¹¹ - 1 ×10¹²) cm^-2 eV^-1 are obtained.

Conventional 1D single level transmission line model (TLM) to extract silicide-silicon contact resistivity does not take into account silicide sheet resistance. In this paper, 1D dual level TLM model approximation is used for extraction of the silicide sheet resistance and silicide-silicon contact resistivity. Experiments involving Platinum content increase in Nickel Silicide and pre-silicide Carbon implant in Silicon Germanium (SiGe) PMOS is analyzed using our model.

The porous silica low-k thin films were deposited by using Sol-gel spin coating technique. The tetraethylorthosilicate (TEOS) was used as a source of Si and the porogen Tween 80 was used for the introduction of porosity of the films. The chemical bondings of porous low-k SiO₂ films have been realized by using Fourier transform infrared spectroscopy (FT-IR). The appearance of stretching, bending and rocking peaks at 1075.8, 967, 426 cm-1 respectively confirms the formation of Si-O-Si network. The Refractive index (RI) and thickness of the films were determined by using ellipsometer. Further, from RI the density and porosity of the films was estimated using standard formula. As from results it’s seems that the density of the films reduces after the addition of Tween 80. The lowest value of films density after the addition of Tween 80 was found to be 1.27 g/cm³. The reduction in the film density results in increase of the porosity of films due to the removal of porogen during the curing. The increase in film porosity from 6% to 45% resulted in lower in the dielectric constant to 2.58.

FinFET is a key device architecture for the 22-nm CMOS and beyond technology nodes. If special care is not taken, these devices could suffer from high series resistance due to the narrow width of their source/drain regions. Using the electrical characterization of fabricated devices, we extract and analyze the dominant component of this series resistance, namely the source/drain contact resistance.