At present efforts in IR detector research are directed towards improving the performance of single element devices and large electronically scanned arrays, and to obtain higher operating temperature of detectors. Another important aim is to make IR detectors cheaper and more convenient to use. Investigations of the performance of narrow gap semiconductor photodiodes are presented. Recent progress in different IR photodiode technologies is discussed: HgCdTe photodiodes, InSb photodiodes, alternative to HgCdTe III-V and II-VI ternary alloy photodiodes, and monolithic lead chalcogenide photodiodes. Investigations of the performance of photodiodes operated at short wavelength IR, 1-3 $mUm; medium wavelength IR, 3-5 micrometers ; and long wavelength IR, 8- 14 micrometers ; are presented. The operating temperature for HgCdTe detectors is higher than for other types of photon detectors. HgCdTe detectors with background limited performance operate with thermoelectric coolers in the medium wavelength range, instead the long wavelength detectors operate at approximately equals 100 K. HgCdTe is characterized by high absorption coefficient and quantum efficiency and relatively low thermal generation rate compared to other detectors.

Electric and optical properties of IR photodiodes based on InAs/(GaIn)Sb superlattices were investigations. Mesa diodes were fabricated with cut-off wavelengths ranging from 7.5 to 12 micrometers , showing 77 K detectivities between 1 X 10¹² cmHz^0.5/W and 5 X 10¹⁰ cmHz^0.5/W, respectively. At least two leakage current mechanisms are observed in the reverse bias branch of the current-voltage characteristics. At high reverse bias band-to-band tunneling currents dominate. Close to zero voltage surface leakage currents become important. The leakage currents are studied with gate controlled mesa diodes, allowing depletion or inversion of the mesa side walls. In addition, the band-to- band tunneling currents are investigated by applying magnetic fields oriented parallel and perpendicular to the electric field across the p-n junction of the diode.

We report on the growth and characterization of InAs/InGaSb type-II superlattices (SLs) designed with a photoresponse cut-off wavelength of 10 micrometers . The structural parameters, layer thicknesses and compositions, were chosen to optimize the IR absorption for a superlattice with an energy band gap of 120 meV. The energy band structure and optimized absorption coefficient were determined with an 8 X 8 envelope function approximation model. The superlattices were grown by molecular beam epitaxy and comprised of 100 periods of 43.6-angstrom InAs and 17.2-angstrom In_.23Ga_.77Sb strain balanced to the GaSb substrates. In order to reduce the background carrier concentrations in this material, SLs grown with different substrate temperatures were compared before and after annealing. The measured photoresponse cut-off energies of 116 +/- 6 meV is in good agreement with the designed value for the SLs. The intensity of the measured mid-IR photoresponse was found to improve by an order of magnitude for the SLs grown at the lower substrate temperature and then annealed at 520 degrees C for 10 minutes. However, the x-ray diffraction spectra were very similar before and after annealing. The temperature dependent Hall measurements at low temperatures were dominated by holes with quasi 2D behavior.

We report the molecular beam epitaxial growth and characterization of InAs/GaSb superlattices grown on semi- insulating GaAs substrate for long wavelength IR detectors. Photoconductive detectors fabricated from the superlattices showed 80 percent cut-off at 11.6 micrometers and peak responsivity of 6.5 V/W with Johnson noise limited detectivity of 2.36 X 10⁹ cmHz^1/2/W at 10.7 micrometers at 78 K. The responsivity decreases at higher temperatures with a T_-2 behavior rather than exponential decay, and at room temperature the responsivity is about 660 mV/W at 11 micrometers . Lower Auger recombination rate in this system provides comparable detectivity to the best HgCdTe detectors at 300K. Higher uniformity over large areas, simpler growth and the possibility of having read-out circuits in the same GaAs chip are the advantages of this system over HgCdTe detectors for near room temperature operation.

Novel interdigitated metal-semiconductor-metal structures offer new approaches for the development of broad-area, high-speed photodetectors to be used in optical free space communications and light detection and ranging applications. Inherent advantages include: lower capacitance than typical p-i-n structures, a wide dynamic range, and ease of fabrication. We have constructed broad area metal- semiconductor-metal photodetectors (MSM-PDs) by means of epitaxial liftoff and grafting technologies. Two computer models have been used to examine the effects of design parameters on the performance of broad-area, high-speed MSM- PD devices. The first model indicates that inverting the membrane so that the electrodes are placed between the non- conducting host substrate and the semiconductor material improves the signal-to-noise ration of the device, expanding its dynamic range. This model suggests that processing of the backside of the semiconductor material with antireflection coatings further improves device performance. Carrier collection behavior described by the second model suggests new electrode configurations for improved high speed operation which can only be applied to an inverted MSM-PD carried on a thin film membrane. A number of different fully passivated large area MSM-PD configurations have been fabricated and tested. Initial dark current data are compared favorably to published results.

Multiplied shot nose and gain-voltage characteristics of separate absorption, grading, charge and multiplication avalanche photodiodes were measured at 25 degrees C in a gain range of 3 to 30. Low optical input powers and a small spot size were used in order to minimize gain saturation effects and gain non-uniformity within the spot. The InP multiplication layer thickness and charge sheet density were extracted from capacitance - voltage characteristics and confirmed by SIMS. Electron and hole impact ionization coefficients in InP were then extracted using gain-voltage characteristics and McIntyre's expressions. Possible deep level traps within the InP multiplication layer were characterized using temperature and frequency characteristics of capacitance - voltage measurements. Peripheral and active area capacitances were separated by studying devices with different active area diameters.

The modifications of the basic photoelectric properties in visible Si photodiodes irradiated by laser pulses have been measured and an attempt to link them to the observed/computed dopant distribution has been performed. These detectors have been irradiated 'in band' with two types of lasers: 1) a Q-switched Nd:YAG laser, frequency doubled with a 'short' pulse duration of 4 ns and 2) dye laser R6G with a 'long' pulse of 2 microsecond(s) . The single pulse fluence range extended form 0.4 to 50 J/cm² well above the surface melting fluence threshold. Specially manufactured detectors have been tested. These detectors have a linearly graded junction with different resistivities. The detector responsivity decrease (DRD) vs applied irradiation fluence has been measured for both irradiation types. SIMS has been used to measure the changes in the dopant profile. It has been shown that a large spreading with a 'plateau like shape' of the boron distribution is obtained, resulting from a gas phase diffusion of dopant during the vaporization/condensation cycle. A relationship between DRD and boron profile has been established for Si detectors irradiated by the dye laser. A local sensitivity drop of 70 percent inside the damaged area location has been measured. Furthermore, it has been shown that high irradiation fluences induce a sequential loss of the different photoelectric properties rather than a complete detector breakdown at a prescribed fluence threshold.

An 'electrode-free' transient photoconductivity technique was applied to investigate excitation, drift and recombination of non-equilibrium free charge carriers in high quality synthetic polycrystalline diamond films, natural diamond crystals and low-conductive GaAs with a time resolution better than 200 ps. Picosecond laser pulses of UV, visible and Ir spectral range were applied for single- photon excitation of free charge carriers with initial concentrations of (10¹²-10¹⁹) cm^-3. Dependences of amplitude and duration of photocurrent on laser intensity/carrier density were measured. Lifetimes, drift mobilities and carrier photoexcitation cross sections as a function of electron concentration were estimated. Computer calculations of conduction and displacement currents, induced space charge and electric field spatial distribution have been performed for the real experimental conditions. Based on the obtained results, high voltage diamond-based switches triggered by ultra-short laser pulses have been designed. Special attention was paid to metal- dielectric interface investigation and ohmic contacts formation. The developed diamond-base module permitted to switch electric fields as high as 100 kV/cm within a time interval less than 200 ps. The amplitude of photocurrent reached 100 A and the electrical resistance reduce by a factor of 10¹⁰.

Quantum well intersubband photodetectors (QWIPs) are potentially important devices for mid- and long-IR wavelengths, especially for focal plane arrays and two-color applications. State-of-the-art QWIPs for detecting light in the mid-IR wavelength range consist of multiple InGaAs quantum wells separated by AlGaAs barriers. The multiple strained InGaAs wells necessary for detection in this wavelength range inevitably lead to lattice relaxation in the epitaxial structure. We have previously demonstrated that the dark current of InGaAs/GaAs QWIPs for detection near 14 microns could be reduced significantly by using strain-compensation to reduce the lattice relaxation in the structure. Here we apply strain-compensation to reduce the relaxation of InGaAs/AlGaAs QWIPs designed for mid- wavelength IR response. We demonstrate the growth of 20 periods of 30A In_0.35Ga_0.65As quantum wells separated by 330A barriers which shows no lattice relaxation as measured by asymmetric x-ray diffraction rocking curves. A strain-compensated QWIP with peak response near 5.5 microns is demonstrated with responsivity of 0.07A/W and 105K background limited operation at 5V bias.

In this paper, we have investigated the bandgap tuning in the InGaAs InP multiquantum well structure obtained by impurity-free vacancy diffusion using low temperature photoluminescence (PL). The MQW intermixing was performed in a rapid thermal annealer (RTA) using the dielectric capping materials, SiO₂ and SiN_x. The SiO₂ capping was successfully used with InGaAs cap layer to cause a large bandgap tuning effect in the InGaAs/InP MQW material. The blue shift of bandgap energy after RTA treatment was as much as 185 and 230 meV at 750 degrees C and 850 degrees C, respectively, with its value controllable using annealing time and temperature. Samples with SiO₂-InP or SiN_x- InGaAs cap layer combinations, on the other hand, did not show any significant energy shifts. The absorption spectra taken from the same samples confirmed the energy shifts obtained using PL. The process development can be readily applied to fabrication of photodetectors that are sensitive to wavelength and/or polarization.

Dark current nose measurements were carried out between 10 and 10⁴ Hz at T equals 80K on two InGaAs/InP quantum well IR photo detectors (QWIPs) designed for 8 micrometers IR detection. Using the measured noise data, we have calculated the thermal generation rate, bias-dependent gain, electron trapping probability, and electron diffusion length. The calculated thermal generation rate is similar to AlGaAs/GaAs QWIPs with similar peak wavelengths, but the gain is 50 X larger, indicating improved transport and carrier lifetime are obtained in the binary InP barriers. As a result, a large responsivity of 7.5 A/W at 5V bias and detectivity of 5 X 10$_11) cm (root) Hz/W at 1.2 V bias were measured for the InGaAs/InP QWIPs at T equals 80K.

Interdiffusion effect has been investigated in highly strained InGaAs/GaAs multiple quantum well (MQW) IR photodetector. Impurity-free interdiffusion techniques was utilized via rapid thermal annealing (RTA) using electron- beam evaporated SiO₂ cap layers at temperature 850 degrees C to study the optical and electrical properties of the interdiffused photodetector. Photoluminescence (PL) spectrum is blue shifted and PL linewidth remains almost the same, indicating no strain relaxation and deterioration of the heterostructure quality. Both transverse magnetic and transverse electric IR intersubband transitions are retained and observed after intermixing. The absorption peak wavelength is red shifted continuously from the as grown 10.20 to the interdiffused 10.5 and 11.17 micrometers , respectively, without appreciable degradation in absorption strength for 5 and 10 s annealing. Annealed responsivity spectra of both 0 degrees and 90 degrees polarization are of compatible amplitude and red shifted but with narrower spectra linewidth. Dark current of the annealed devices is found to be an order of magnitude large than the as-grown one at 77K.

Bi/Bi_1-xSb_x multiquantum well structure has been grown by molecular beam epitaxy (MBE) on GaAs(001) substrate with a buffer layer of CdTe (111). The GaAs substrate was preheated at a temperature of 580 degrees C in the MBE chamber with vacuum of 10⁺¹⁰ torr for 10 minutes. The CdTe (111) buffer layer was grown with thickness of 300 nm at temperature of 280 degrees C. The Bi/Bi_1-xSb_x multilayer structure with x of 0.15, repeated 40 times, was grown at substrate temperature of 130 degrees C. As- deposited samples were characterized by reflection high- energy electron diffraction, x-ray diffraction analysis and high-resolution transmission electron microscopy (TEM), indicating a good epitaxial layer quality. The energy band model of the samples have been suggested for the first time.

A corrugated quantum well IR photodetector (C-QWIP) focal plane array (FPA) with cutoff at 11.2 micrometers has been fabricated and characterized. The C-QWIP array uses total internal reflection to couple normal incident light into the pixels. The processing steps involve only one chemical etching, one optional reactive ion etching, and one ohmic contact metalization. The detector array has 256 X 256 pixel elements, indium bumped to a direct injection readout circuit. The photocurrent to dark current ratio measured in this FPA, on which the noise equivalent temperature difference depends, is consistent with that of a large area test sample. The array shows good responsivity uniformity of 5.2 percent with no extra leakage resulted from array processing. The estimated noise equivalent temperature difference of this array, excluding the readout noise, is 17 mK at T equals 63 K. The fact that this FPA can be operated at a temperature similar to those of standard QWIP arrays with much shorter wavelengths shows that the C-QWIP structure can greatly increase array performance.

Progress on mid-IR photodetectors fabricated by the liquid phase epitaxial growth of GaInAsSb and InAsSbP on GaSb and InAs substrates is reported. GaInAsSb p/n and p-i-n detectors and InAsSbP p/n detector structures were fabricated. Preliminary results indicate that these devices can have higher detectivity with lower cooling requirements than commercially available detectors in the same wavelength range. IR p/n junction detectors made from GaInAsSb and InAsSbP showed cut-off wavelengths of 2.3 micrometers and 2.9 micrometers respectively. Room temperature background noise- limited detectivity of 4 X 10¹⁰ cmHz^1/2/W GaInAsSb detectors and 4 X 10⁸ cmHz^1/2/W for InAsSbP was measured.

A process for fabrication of low-frequency, low-noise, low- power silicon JFETs for cryogenic operation has been developed. COmmercially available silicon JFETs exhibit very high low frequency and 1/f noise at liquid nitrogen temperature. We report on process optimization and effect of high temperature oxidation and drive-in process on noise performance of these devices. These silicon JFETs were designed for operation at 77K. In this paper, we report the noise performance and its relation to the well-known complex oxygen-vacancy. A center that has a trap level of 0.18 eV below the conduction band. These devices were developed for use in the photo-diode assembly of NASAs Gravity Probe B mission telescope.

The measurement of heterojunction band parameters and their spatial variation is of fundamental importance for the operation of heterostructure devices. Ballistic electron emission microscopy (BEEM) is a powerful, new low energy electron microscopy for imaging and spectroscopy of buried quantum objects and non-destructive local characterization of buried semiconductor heterostructures with nm resolution. We will present several new and novel applications of BEEM for semiconductor heterostructure characterization.

We present results on p-type quantum well IR photodetectors (QWIPs) based on GaAs substrates, and discuss issues related to the optimization of their performance. Due to the fact that a p-QWIP allows normal incidence absorption, the simplicity in device fabrication makes it interesting for implementing a pixel-less imaging device based on the integration of QWIP and light emitting diode.

The noise spectral density off current fluctuations in single quantum well IR photodetectors is calculated using Langevin approach. Fluctuations of the incident photon flux ar taken into account. The dark current noise spectral density has a Lorentzian shape with characteristics frequency equal to inverse time of the QW recharging. This effect is due to the modulation of the injection current by the charge in the QW. The noise gain and the photocurrent gain are expressed in terms of basic transport parameters. The ratio of the noise gain to photocurrent gain is different from unity in general case.

The calculation of the dark currents existing in a AlGaN/GaN quantum well IR photodetector is presented in this paper. The dark current is calculated from the electrons following from the n⁺ region through the top barrier and not from out of the quantum well. This is a result of the number of electron emitting a quantum well equaling the number of electrons being captured, resulting in a zero net current. The calculation of the current accounts for the redistribution of the density of states and the local velocity arising form the multiple quantum well structure. A comparison of the experimental results to the theoretical calculation of the transmission coefficient, the local velocity and the density of states demonstrate that the variation in the dark currents is a result of the variation in the growth process from one structure to another and not a function of the number of quantum wells. A comparison is made between an AlGaAs/GaAs based system and an AlGaN/GaN based system demonstrating a large reduction in the dark current.

Using MOCVD grown GaN and AlGaN alloys and heterostructures, we realized heterojunction UV photodiodes and phototransistors. We achieved photovoltaic internal quantum efficiency in excess of 90 percent and large UV-visible rejection ratio in the GaN/AlGaN PIN photodiodes. The results indicate high quality heterojunction interface and efficient carrier collection. We demonstrated an n-p-i-n GaN/AlGaN heterojunction bipolar phototransistor with gain in excess of 10⁵, and 360 nm to 400 nm rejection ratio of 10⁸. The phototransistor features a rapid electrical quenching of photoconductivity therefore can be operated without DC drift, an option not available in unipolar photoconductors. The electrical bandwidth of the phototransistor can be changed to accommodate particular applications by simply adjusting the repetition rate of the quenching pulses. The operation and evaluation of these devices are compared with alternative devices including SiC photodiode and GaN photoconductors.

This paper discuses recent results of time response and spectral responsivity measurements made on Al_xGa_1-xN/GaN-based p-i-n UV detector with .03 < x < 0.12, where x is the aluminum concentration. Al_xGa_1-xN/GaN-based p-i-n detectors with response times as fast as 6 ns corresponding to greater than 26 MHz bandwidths are reported. Peak spectral responsivities of homojunction Al_.03Ga_.97N p-i-n UV detectors were found to be as high as 0.08 A/W at 343 nm while those of the Al_.1Ga_.9N/GaN p-i-ns were as high as 0.15 A/W at 360 nm. Homojunction GaN and Al_.03Ga_.97N as well as p-Al_.1Ga_.9N/i-GaN/n-GaN structures were grown on sapphire substrates by reactive molecular beam epitaxy and processed into UV detectors. These p-i-n detectors were then characterized in terms of their time response and spectral responsivity. Attempts to measure the noise of the Al_.03Ga_.97N homojunction p-i-ns are also discussed.

At present, the main efforts in fabrication of UV photodetectors are directed to GaN Schottky barriers and p-n junction photodiodes. The future development of UV photodetectors will be dominated by complex band gap heterostructures using 3D gap and doping engineering. AlGaN exhibits extreme flexibility, it can be tailored for optimized detection at important regions of UV spectrum, and multicolor devices can be easily constructed. The comparative study of GaN Schottky barriers and p-n junction photodiodes are carried out in more details. Due to the fact that the built-in voltage of a Schottky diode is smaller than that of a p-n junction, the saturation current of a Schottky barrier is considerably higher than that of p-n junction. Special attention has been devoted on analysis of current responsivities of both types of detectors. Owing to relative simplicity in fabrication of Schottky barriers, they can be more promising than p-n junction detectors, especially in the case of low doping ensuring the entire depletion of the n-type layer.

UV photodetectors are critical components in many applications, including UV astronomy, flame sensors, early missile threat warning and space-to-space communications. Because of the presence of strong IR radiation in these situations, the photodetectors have to be solar blind, i.e. able to detect UV radiation while not being sensitive to IR. Al_xGa_1-xN is a promising material system for such devices. Al_xGa_1-xN materials are wide bandgap semiconductors, with a direct bandgap whose corresponding wavelength can be continuously tuned from 200 to 365 nm. Al_xGa_1-xN materials are thus insensitive to visible and IR radiation whose wavelengths are higher than 365 nm. We have already reported the fabrication and characterization of Al_xGa_1-xN- based photoconductors with a cut-off wavelength tunable from 200 to 365 nm by adjusting the ternary alloy composition. Here, we present the growth and characterization of GaN p-i- n photodiodes which exhibit a visible-to-UV rejection ratio of 6 orders or magnitude. The thin films were grown by low pressure metalorganic chemical vapor deposition. Square mesa structures were fabricated using dry etching, followed by contact metallization. The spectral response, rejection ratio and transient response of these photodiodes is reported.

Computational materials science has evolved in recent years into a reliable theory capable of predicting not only idealized materials and device performance properties, but also those that apply to practical engineering developments. The codes run on workstations and even now are fast enough to be useful design tools. A review will be presented of the current status of this rapidly advancing field.As a demonstration of the power of the methods, predictions of the native point and complex defect, and impurity densities for the Hg_0.8Cd_0.2Te alloy as functions of external processing conditions will be treated. Where measurements have been done, the observed values agree well with the predictions. As an example, we find that As incorporates predominately on the cation sublattice, if the material is grown form the Te side of the existence curve, whereas it tends to reside on the anion sublattice in Hg-saturated growth. On the cation sublattice As is a donor. It is an acceptor on the Te sublattice. We have devised a post-MBE- growth processing method to encourage the transfer of As form the cation to the anion sublattice. Those aspects of the proposed process that have been tested work.

IR detectors are normally cooled to 80K or below to obtain the highest, background limited performance. We present results for indium antimonide/indium aluminium antimonide and mercury cadmium telluride detectors grown by epitaxial processes in order to facilitate high performance with reduced cooling requirements. The epitaxial growth enables structures to be grown which offer precise control of carrier generation and current leakage mechanisms so that the maximum temperature can be achieve din a photodiode operated in a conventional manner, near zero bias. These types of structure offer even greater operating temperature when reverse biased to suppress non-radiative generation mechanisms. The epitaxial growth also has advantages for conventional, 80K operation, which are described.

We obtained the photoluminescence spectra for CdTe(111) grown on Si(100) tilted toward <011> 1 degree, 2 degrees, 4 degrees and 8 degrees by MBE before and after RTA. It is caused by the strain due to the lattice mismatch between CdTe epitaxial layer and the substrate that the shift of peaks form CdTe(111)/Si(100) epitaxial layer was observed comparing with that of bulk. We could guess the crystal structures of the CdTe(111) epitaxial layers from the strains calculated from the quantity of the shifts. We found that the crystal structure of CdTe changed from the cubic in bulk to the tetragonal in strained as-grown samples, and from the tetragonal to the trigonal after RTA. It is caused by the different strain type that the structures are different before and after RTA because the misfit for atomic distance is dependent on the direction between CdTe(111) and Si(100). We found that the inplain compressive strains change from asymmetry to symmetry about (111) direction in CdTe(111) epitaxial layer after RTA.

We report on the growth and investigation of InTlSb and InSbBi alloys for uncooled IR photodetector applications. The epitaxial layers of the materials have been grown on (100) InSb or GaAs substrates by low pressure metalorganic chemical vapor deposition. The incorporation of Tl and Bi has been verified by x-ray diffraction spectra, Auger electron spectroscopy, and energy dispersive x-ray analysis. The maximum incorporation of Tl and Bi estimated from the optical band gap change was 5.6 and 5.8 percent, respectively. The lattice contraction with the incorporation of Tl and Bi was verified by high resolution x-ray diffraction spectra. Tetragonal structure for the InSbBi and hybridized nature for the InTlSb alloys have been suggested to explain this abnormal behavior. The fabrication and characterization of photoconductive detectors based on these material are also reported. Photoresponse of InTlSb photodetectors was observed up to 11 micrometers at 300 K. The maximum responsivity of an In_0.96Tl_0.04Sb photodetector was about 6.6 V/W at 77K, corresponding to a Johnson noise limited detectivity of 7.6 X 10⁸ cmHz^1/2/W. The carrier lifetime in InTlSb photodetectors was 10-50 ns at 77K. The responsivity of the InSb_0.96Bi_0.04 photodetector at 7 micrometers was about 3.2 V/W at 77K with corresponding Johnson noise limited detectivity of 4.7 X 10⁸ cmHz^1/2/W. The carrier lifetime of InSbBi detector was estimated to be about 86 ns from the voltage dependent responsivity measurements. The InSb_0.95Bi_0.05 photodetectors exhibited peak responsivity of 7.0 X 10^-3 V/W with photoresponse up to 12 micrometers and estimated carrier lifetime of 17 ns at room temperature.

The Stratospheric Observatory for Infrared Astronomy, SOFIA, is a joint US and German project and will start observations from altitudes up to 45,000 ft in late 2001. The 2.5 m telescope is being developed in Germany while the 747- aircraft modifications and preparation of the observatory's operations center is done by a US consortium. Several research institutions and universities of both countries have started to develop science instruments. The DLR Institute of Space Sensor Technology in Berlin plans on a spectral-photometric camera working in the 20 to 220 micrometers wavelength range, using doped silicon and germanium extrinsic photoconductors in large, 2D arrays: silicon blocked-impurity band detectors, Ge:Ga and stressed Ge:Ga. While the silicon array will be commercially available, the germanium arrays have to be developed, including their cryogenic multiplexers. Partner institutions in Germany and the US will support the development of the instrument and its observations.

A high performance, bias tunable, p-GaAs homojunction interfacial workfunction internal photoemission far-IR detector has been demonstrated. A responsivity of 3.10 +/- 0.05 A/W, a quantum efficiency of 12.5 percent and a detectivity D* of 5.9 X 10¹⁰ cm (root) Hz/W, were obtained at 4.2K, for cutoff wavelengths from 80 to 100 micrometers . The bias dependences of quantum efficiency, detectivity, and cutoff wavelength have been measured and are well explained by the theoretical models, where the cutoff wavelength is modeled by a modified high density theory, and the quantum efficiency is predicted by scaling the free carrier absorption coefficient linearly with the doping concentration. The effect of the number of layers on detector performance and the uniformity of the detectors have been discussed. A comparison with Ge:Ga photoconductive detectors suggest that a similar or even better performance may be obtainable.

The results of experimental and theoretical investigations of the noise properties of high-Tc superconducting films and bolometers are reported. YBaCuO and GdBaCuO films produced by magnetron and laser deposition on various substrates were studied. The effect of various noise components on the noise equivalent power (NEP) of different bolometers is considered. Structural, noise and critical current properties were investigated. Using the laser ablation YBaCuO films with very low noise Hooge's parameter close to 2 X 10^-4 was obtained. Experimental data are discussed on basis of the modern excess low frequency l/f models. Besides, the noise measurements of antenna YBaCuO microbolometers on NdGaO₃ substrate and GdBaCuO bolometers on Si-membrane are reported. The NEP equals 1.2 X 10^-11 W/Hz^1/2 at response time of 0.3 microsecond(s) for microbolometer and D* equals 3.8 X 10⁹ cmHz^1/2W^-1 at response time of 0.45 ms for bolometer on Si-membrane were reached. NEP of the bolometers is limited by only the phonon noise.

As is well known, lateral superlattices on semiconductor vicinal planes are realized in 2D electron systems on high-index Miller surfaces. In this work we suggest a new method of development of vicinal superlattices in quantum wires on semiconductor low-index surfaces. For this purpose we suggest to orient the axis of the wire at the necessary angles to the basic translation vectors on a low-index surface (for instance, in the MOS system with the use of a narrow gate). In this case in the quantum wire the new basic translation period along the axis of the wire A< < a0 (ao - lauice constant) appears. Keywords: quantum wire, vicinal superlattice, low-index surface, energetic spectrum, nünigaps.

We have investigated the selective formation of In_xGa_1-xAs quantum dots by molecular beam epitaxy. Particularly, we report on selectivity formed In_xGa_1-xAs QDs on the GaAs(100) substrate with fine- patterned oxide layers such as gallium oxide and silicon oxide, which are prepared with electron bema lithography technique. The electron beam lithography pre-patterned oxide layers were used to assemble the dots in a specific region. Both of the oxide layers served as mask materials were compared for the better selective growth of self-assembled QDs. The migration and the desorption of the In and Ga adatoms on the oxide layers are considered to be the most important factors for the selective formation of In_xGa_1-xAs quantum dots by molecular beam epitaxy. The influences of the mole fractions of indium, the growth temperature and the growth interruption times on the morphological transformation from 2D to 3D structures were discussed. Particularly, the 2D arrays of quantum dots selectively formed on GaAs substrates with pre-patterned Ga₂O₃ oxide layer may eventually be used for novel electronic or optical devices.

The photoelectric transient process of a 99 period Si_0.823Ge_0.177/Si superlattices (SL) was investigated by the photocurrent decay (PCD) method. Decay lifetimes of electron and hole in SL, Si cap and buffer layers are extracted from the transient intensity and polarity of the PCD signal. The temperature and bias dependences of lifetime exhibit the thermalization of heavy hole, the dissociation of free exciton, and the thermal activation of shallow impurity and dislocation. The thermalized hole jumps in and out of the well at low temperature and weak electric field, while it jumps or surfs over the well region by a strong electric field or at high temperature. The lifetimes of electron and hole are nearly the same in the Si cap layer, while the lifetime of hole is about one order of magnitude longer than that of electron in SL, possibly due to the quantum confinement of hole in the SL region.

Temperature-dependent Hall-effects in MOCVD-grown Si-doped GaN epilayers were measured as a function of temperature in the range 10-800 K. The results were satisfactorily analyzed in terms of a two-band model including the (Gamma) and impurity bands at lower temperatures than room. The (Gamma) band electrons are dominant only high temperatures. The ionized impurity scattering is the most important in the (Gamma) band except at very high temperatures.

In this study, we report the RF magnetron sputtering growth and characterization of CdTe passivant on bulk n-type HgCdTe. Our investigations include the HgCdTe surface preparation and in-situ pretreatment, deposition-induced surface damage, interface charge, CdTe film stoichiometry, and thermal stability. The metal-insulator-semiconductor test structures are processed and their electrical properties are measured by capacitance-voltage characteristics. The heterostructures are also characterized by reflectance measurement. In order to investigate the passivation properties of CdTe/HgCdTe heterostructures, we have modeled the band diagram of abrupt CdTe/HgCdTe heterojunction. The effect of sputtering growth condition parameters is also reported. The sputtering CdTe layers, exhibit excellent dielectric, insulating and mechano- chemical properties, as well as interface properties. The interfaces are characterized by slight accumulation and a small hysteresis. A carefully controlled growth process and surface pretreatment tailored to the specific material are required in order to obtain near flat band conditions on n- type materials. Additional informations on surface limitations are obtained from analyzing the I-V characteristics of photodiodes with metal gates covering the p-n junction surface location.

The paper describes the new achievements in an all solid state photon counting technique with picosecond resolution. The extended dynamical range has been achieved: the dependence of the detection delay on the detected signal strength - the time walk -has been compensated within several orders of optical signal strength. The principal application of the detector is the millimeter resolution satellite laser ranging. The detector is based on silicon avalanche photodiode pulse biased above its break voltage. The external gating and avalanche active quenching electronics is used. The time walk of the avalanche photodiode is of the order of hundreds of picoseconds in the dynamical range of single to one hundred photons input signal strengths. The additional electronics circuit has been developed to compensate for the time walk: the input optical signal strength influences the avalanche current build up time,the maximum build up time difference is 20 psec within the dynamical range 1:1000. This time difference is sensed, stretched by the factor of ten. The stretched time interval is applied, with the negative sign, as a correction to the detector propagation delay. The detector ultimate timing resolution, temporal stability, dynamical range and its dependence on the input laser pulse length have been investigated in detail. The fieldable version of the detector is been used for satellite laser ranging purposes. The timing resolution of the entire detector better than 20 picoseconds r.m.s., the maximum dynamical range > 1000:1 with the item walk bellow +/- psec have ben achieved, the results are presented. The additional applications in spectroscopy, biophysics, rangefinding and fiber optics may be considered.

The effects of rf-bias to the substrate on the defects of hydrogenated amorphous silicon deposited by electron cyclotron resonance - plasma enhanced chemical vapor deposition were investigate.d Measurements by constant photo-current method showed that the defect density decreased as the rf-power increased. The decrease of the defect density by rf-bias did not depend on the microwave power so much. Deposition rate did not depend on the rf- power, whereas it increased with the increase of the microwave power. Photoconductivity was shown to increase with rf-power corresponding to the decrease of the defect density. Surface roughness measurements indicated that the surface flatness was increased by rf-bias voltage independently of the deposition temperature. It was considered that these elimination of defects was induced by the increase of the number of mobile particles on the surface due to rf-bias.

A simple grating mask has been used in an ordinary 5:1 projection stepper equipment to fabricate microscopic parabolic topographies in thick positive photoresist. The microparabolic surfaces created were coated with reflective material to form parabolic reflectors. Measurement values of focal length were in agreement with the expected theoretical values. The simple parabola forms the basis for the fabrication of compound parabolic reflector which can be used for beam steering. Normal incidence beam can be redirected by the compound parabolic reflector onto device areas in the vicinity of the focus.

AlGaN based interdigital metal-semiconductor-metal (MSM) photodetectors with 14 percent Al have been successfully grown and fabricate don sapphire substrates. The devices exhibit large gains up to 10⁶ at high bias voltages, but with very high dark currents, > 1 mA and very long detector responses, > 60 seconds. A negative temperature coefficient for the breakdown voltage was observed indicating that tunneling is occurring. However, at high bias voltages, avalanche breakdown also appears to be present since a constant breakdown field of 10⁵ V/cm was obtained independent of MSM geometry. Avalanche breakdown is nucleated at the non-uniform field distribution at the edge of the MSM finger.

One of the simplest device realizations of the classic particle-in-the-box problem of basic quantum mechanics is the quantum well IR photodetector (QWIP). In this paper we discuss the optimization of the detector design, material growth and processing that has culminated in realization of 15 micron cutoff 128 X 128 QWIP focal plane array camera, hand-held and palmsize 256 X 256 long wavelength QWIP cameras and 648 X 480 long-wavelength cameras, holding forth great promise for myriad applications in 6-25 micron wavelength range in science, medicine, defense and industry. In addition, we present the recent developments in broadband QWIPs and mid-wave long-wave dualband QWIPs at Jet Propulsion Lab for various NASA and DOD applications.