This PDF file contains the front matter associated with SPIE Proceedings Volume 10114, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

Nanowire (NW) lasers have recently attracted increasing attention as ultra-small, highly-efficient coherent light emitters in the fields of nanophotonics, nano-optics and nanobiotechnology. Although there have been several demonstrations of single NW lasers utilizing bulk materials, it is crucial to incorporate lower-dimensional quantum nanostructures into the NW in order to achieve superior device performance with respect to threshold current, differential gain, modulation bandwidth and temperature sensitivity. The quantum dot (QD) is a useful and essential nanostructure that can meet these requirements. In this presentation, we will talk about our recent research activity regarding room temperature lasing of a single GaAs NW containing 50-stacked In_0.2Ga_0.8As/GaAs QDs. The NW cavities consist of multiple In_0.2Ga_0.8As/GaAs heterostructures acting as a QD active material, which are grown on shallow (<45 nm) GaAs core NWs and followed by GaAs/Al_0.1Ga_0.9As/GaAs core/shell/cap structures. Lasing oscillation is achieved at the emission wavelength of 900 nm by properly designing the NW cavity and tailoring the emission energy of each QD to enhance the optical gain. Obtained threshold pump pulse fluence is 179 μJ/cm² at room temperature and the characteristics temperature is 133K which is higher than that of conventional bulk NW lasers. Our demonstration paves the way toward ultra-small lasers with extremely low-power consumption for integrated photonic systems. Furthermore, we will discuss our recent results on the demonstration of several types of NWQD lasers in order to improve the device performance of the NWQD lasers.

In this work, we study the optical properties and emission dynamics of the novel nanostructure p-GaAs nanopillars (NPs) on Si. The integration of III-V optoelectronics on Si substrates is essential for next-generation high-speed communications. NPs on Si are good candidates as gain media in monolithically integrated small-scale lasers on silicon. In order to develop this technology, an in-depth knowledge of the NP structure is necessary to resolve its optimal optical properties.

The optical characterization which has been carried out consists of the emission analysis for different NP geometries. We measured NPs with different combinations of pitch (of the order of a few μm) and diameter (of the order of tens of nm). A comparison of intensities for the various NPs provides us with the most efficient geometry. The quality of the crystal grown has been studied from temperature-dependent photoluminescence (PL). A red shift and a significant reduction of the intensity of the NP emission are observed with an increase in temperature. The results also show the presence of two non-radiative recombination channels when the intensity peaks at different temperatures are analyzed with the activation energy function.

In this paper, we discuss recent progress obtained on infrared nanocrystal based on mercury chalcogenides (HgTe and HgSe). These materials can become some key building blocks for the next generation of infrared optoelectronic devices. To reach this goal, the infrared nanocrystals need to combine fine control on the optical features and efficient electronic transport. Here, we report about (i) the development of HgTe NPL for enhanced optical features (narrower and faster PL) in the near IR and (ii) about the development of self-doped nanocrystals of HgSe to demonstrate tunable intraband absorption up to the THz range.

Efficient coupling of nanoemitters to photonic or plasmonic structures requires the control of the orientation of the emitting dipoles. Nevertheless controlling the dipole orientation remains an experimental challenge. Many experiments rely on the realization of numerous samples, in order to be able to statistically get a well aligned dipole to realize an efficient coupling to a nanostructure. In order to avoid these statistical trials, the knowledge of the nature of the emitter and its orientation is crucial for a deterministical approach. We developed a method [1],[2] relying on the combination of polarimetric measurement and emission diagram which gives fine information both on the emitting dipolar transition involved and on the dipolar orientation We analyse by this method square and rectangle single colloidal CdSe/CdS nanoplatetelets. We demonstrate that their emission can be described by just by two orthogonal dipoles lying in the plane of the platelets. More surprisingly the emission of the square nanoplatelets is not polarised whereas the rectangle one is. We demonstrate that this polarized emission is due to the rectangular shape anisotropy by a dielectric effect. [1] C. Lethiec, et al, Three-dimensional orientation measurement of a single fluorescent nanoemitter by polarization analysis, Phys. Rev. X 4, 021037 (2014), [2] C. Lethiec et al, Polarimetry-based analysis of dipolar transitions of single colloidal CdSe/CdS dot-inrods, New Journal of Physics 16, 093014 (2014) [3] S. Ithurria et al, colloidal nanoplatelets with 2 dimensional electronic structure, Nature Materials 10, 936 (2011)

Scaling down semiconductor lasers in all three dimensions hold the key to the developments of compact, low-threshold, and ultrafast coherent light sources, as well as photonic integrated circuits. However, the minimum size of conventional semiconductor lasers utilizing dielectric cavity resonators (photonic cavities) is constrained to the diffraction limit. In the past few years, it has been experimentally demonstrated that the use of plasmonic cavities based on metal–oxide–semiconductor (MOS) structures can break this limit. In this presentation, I will report on the recent progress of plasmonic nanolasers using MOS structures. In particular, by using alloy-composition-varied indium gallium nitride/gallium nitride (InGaN/GaN) core–shell nanorods as the nanolaser gain media in the full visible spectrum, we are able to demonstrate full-color nanolasers that can be operated with ultralow CW lasing thresholds and single lasing modes. Full-color lasing in these subdiffraction plasmonic cavities is achieved via a unique autotuning mechanism based on a property of weak size dependence inherent in plasmonic nanolasers. As for choice of metals in the MOS structures, epitaxial Ag films and giant colloidal Ag crystals have been shown by us to be the superior constituent materials for plasmonic cavities due to their low plasmonic losses in the visible spectral range. Recently, we have also succeeded in developing InGaN/GaN nanorod array plasmonic lasers based on a metal (Au)-all-around MOS structure, which can be fabricated easily on a wafer scale. I will present the latest results in these developments.

Selective Area Growth (SAG) by Molecular Beam Epitaxy (MBE) is one of the best approaches to develop a variety of nanostructures on different substrates. Ordered axial InGaN/GaN nanoLED structures were grown on GaN/sapphire templates as well as on GaN buffered Si(111) substrates. Core-shell InGaN/GaN microstructures can also be grown following two approaches: i) from top–down (etched) GaN cores and ii) from bottom-up GaN cores. In both cases a subsequent conformal growth of InGaN layers was achieved. Based on this approach, core-shell nanoLED arrays were successfully fabricated. A basic aspect of SAG refers to the initial stages of nanocrystals nucleation within the nanoholes that lead to their stable hexagonal structure and the efficient filtering of dislocations coming from the substrate, strongly dependent on the nano/microrod geometry. A common observed feature is that In incorporation depends strongly on the crystal plane considered, either m- or r-plane, giving rise to two InGaN related emissions. Exploiting this effect, dot-in-a-wire InGaN structures were grown embedded in ordered GaN nanorods acting as Single Photon Emitters. Nano/microrods can also be used as nanoFET transistors with a semi-cylindrical gate direct contact allowing for a very tight electrostatic control of the channel. SAG is also used to grow ordered nanostructures on semi-polar and non-polar orientations GaN/sapphire templates with the aim to fabricate ternary pseudo-substrates with tailored lattice constant and very high crystal quality.

Nanowires offer new opportunities for nanoscale quantum optics; the quantum dot geometry in semiconducting nanowires as well as the material composition and environment can be engineered with unprecedented freedom to improve the light extraction efficiency. Quantum dots in nanowires are shown to be efficient single photon sources, in addition because of the very small fine structure splitting, we demonstrate the generation of entangled pairs of photons from a nanowire. By doping a nanowire and making ohmic contacts on both sides, a nanowire light emitting diode can be obtained with a single quantum dot as the active region. Under forward bias, this will act as an electrically pumped source of single photons. Under reverse bias, an avalanche effect can multiply photocurrent and enables the detection of single photons. Another type of nanowire under study in our group is superconducting nanowires for single photon detection, reaching efficiencies, time resolution and dark counts beyond currently available detectors. We will discuss our first attempts at combining semiconducting nanowire based single photon emitters and superconducting nanowire single photon detectors on a chip to realize integrated quantum circuits.

Nanowires (NWs) have better functionality and superior performance as compared with the traditional thin film counterparts. However, NW growth is highly complicated and the growth mechanism is far from clear, especially when it is grown by vapor-liquid-solid mode. In this work, the influences of droplet size on the growth of self-catalyzed ternary NWs were studied using GaAsP NWs. The size-induced Gibbs−Thomson (GT) effect is observed for the first time in the self-catalyzed growth mode, which can make the smaller catalytic droplets have lower effective supersaturations. Thus, the droplet size can significantly influence the uniformity and composition of NWs. By carefully control the droplet size, the growth of highly uniform NW arrays are demonstrated. These results provide useful information for understanding the mechanisms of self-catalyzed III−V NW nucleation and growth with the important ternary III−V material systems.

The type-I to type-II band alignment transition in InAlAsAs/AlGaAs/GaAs self-assembled quantum dots (QDs) is investigated when the Al-composition in QDs and barrier are changed. In particular, the In0.46Al0.54As/Ga0.46Al0.54As/GaAs QDs show unique optical properties. The PL peak energy has a blue-shift of >40 meV when the laser intensity increases by four orders of magnitude, indicating a type-II band alignment of the QDs. The formation of the type-II band alignment is explained by that the quantum-confinement effect pulls up the minimum electron energy level in the QDs and the Γ→X transition in the Ga0.46Al0.54As barrier. The time-resolved PL (TRPL) spectrum of QDs at peak wavelength exhibits a double-component decay behavior, suggesting the possibility of type-I and type-II band alignment coexistence in this QD sample. The continuum state of the QDs is also investigated. Emission associated with the continuum states of the QDs is directly observed in PL spectra. The PL excitation (PLE) and TRPL spectra reveal an efficient carrier relaxation from the AlGaAs barrier into the InAlAs QD ground state via the continuum states. The carrier recombination in the continuum states can compete with that in the QDs due to the long recombination lifetime in the type-II QDs. This feature of continuum state emission can not be observed for normal InGaAs/GaAs QDs with the type-I band structure.

Quantum dots based on InAs/InP hold the promise to deliver entangled photons with wavelength suitable for the standard telecom window around 1550 nm, which makes them predestined to be used in future quantum networks applications based on existing fiber optics infrastructure. A prerequisite for the generation of such entangled photons is a small fine structure splitting (FSS) in the quantum dot excitonic eigenstates, as well as the ability to integrate the dot into photonic structures to enhance and direct its emission. Using optical spectroscopy, we show that a growth strategy based on droplet epitaxy can simultaneously address both issues. Contrary to the standard Stranski-Krastanow technique, droplet epitaxy dots do not rely on material strains during growth, which results in a drastic improvement in dot symmetry. As a consequence, the average exciton FSS is reduced by more than a factor 4, which in fact makes all the difference between easily finding a dot with the required FSS and not finding one at all. Furthermore, we demonstrate that droplet epitaxy dots can be grown on the necessary surface (001) for high quality optical microcavities, which increases dot emission count rates by more than a factor of five. Together, these properties make droplet epitaxy quantum dots readily suitable for the generation of entangled photons at telecom wavelengths.

Ga(Sb)As quantum dots (QDs) are usually grown on plane GaAs substrates by self-organization in the StranskiKrastanov mode. Here we report on Ga(As)Sb QD growth on a pre-structured GaAs substrate to achieve highly ordered QDs. The structure consists of a two-dimensional array of holes/troughs milled into the substrate (wafer with initial epitaxial buffer layer) with a gallium focused ion beam (Ga-FIB). Thus, the area density of the QDs can be controled. For exact positioning of the QDs in the milled holes it is important that the diameter of the dots equals the diameter of the milled holes. In a previous publication we have shown that we are able to change the diameter as well as the height of the QDs by controlled variation of growth temperature, Ga/Sb ratio, and nominal coverage. The diameter and depth of the milled holes as well as their separation are varied. Also, different milling techniques are examined to optimize milling time and procedure. The pre-structured GaAs substrate is overgrown in a second molecular-beam-epitaxial (MBE) step, first with another thin GaAs buffer layer, then with a QD layer. With the optimum of the milling and growth parameter sets the diameter of the QDs equals the size of the milled holes and the QDs can be grown highly ordered in the given pre-structured array. To the best of our knowledge this is the first report about exact positioning of Ga(As)Sb QDs on GaAs.

We report a single layer GaAsN/InAs/GaAsN quantum-dot-in-well (DWELL) structure with PL emission at 1.31μm important for applications in communication lasers. This extension has been achieved with a nitrogen composition of only 1.8% and QDs embedded within 1/6nm GaAsN which is higher compared to single layer QDs with GaAs and GaAsN capping layers as a result of confinement reduction on both sides of the QD energy levels. The structures remain as QDs till 800°C of annealing temperature alongwith a drastic enhancement in PL intensity as a result of annihilation of N-induced crystal defects which provide non-radiative recombination centers for carriers in the as-grown sample which is responsible for degraded luminescence. A typical highly asymmetric PL signature observed in dilute nitride structures is seen with a sharp cut-off at lower wavelengths and a large exponential tail at higher wavelengths in the as-grown and 650°C annealed samples. This is due to the presence of localized excitonic states extending into the bandgap close to the band edges. For higher annealing temperatures, this asymmetry disappears indicating an improvement in uniformity of nitrogen distribution and absence of localized states; which is also confirmed from a smaller blueshift in excitation intensity-dependent PL spectra of these samples. Well-resolved ground and first excited states in the PL spectrum of 700°C annealed sample indicates an improvement in QD confinement.

Colloidal semiconductor nanoplatelets (NPLs) are quasi 2D-nanostructures that are grown and processed inexpensively using a solution based method and thus have recently attracted considerable attention. We observe two features in the photoluminescence spectrum, suggesting two possible recombination channels. Their intensity ratio varies with temperature and two distinct temperature regions are identified; a low temperature region (10K < T < 90K) and a high temperature region (90K < T < 200K). This ratio increases with increasing temperature, suggesting that one recombination channel involves holes that are weakly localized with a localization energy of 0.043meV. A possible origin of these localized states are energy-variations in the xy-plane of the nanoplatelet. The presence of positive photoluminescence circular polarization in the magnetically-doped core/multi-shell NPLs indicates a hole-dopant exchange interaction and therefore the incorporated magnetic Manganese ions act as a marker that determines the location of the localized hole states.¹ Time-resolved measurements show two distinct timescales (τ_fast and τ_slow) that can be modeled using a rate equation model. We identify these timescales as closely related to the corresponding recombination times for the channels. The stronger hole localization of one of these channels leads to a decreased electron-hole wave function overlap and thus a decreased oscillator strength and an increased lifetime. We show that we can model and understand the magnetic interaction of doped 2D-colloidal nanoplatelets which opens a pathway to solution processable spin controllable light sources.

Plasmonic and photonic nanoparticles have proven beneficial for solar cells in the aspect of light management. For improved exploitation of nanoparticles in solar cells, it is necessary to reveal the absorption enhancement mechanism from the nanoparticles. In this study, we investigated the nanoparticle-enhanced solar cells in near-field regime with optic and opto-electric scanning near-field optical microscopy (SNOM). The near-field distribution of regularly arranged silver and polystyrene nanoparticles produced by nanosphere lithography on Cu(In,Ga)Se₂ (CIGSe) solar cells is characterized using a custom-built SNOM, which gives insight into the optical mechanism of light trapping from nanoparticles to solar cells. On the other hand, the photocurrent of CIGSe solar cells with and without nanoparticles is studied with an opto-electric SNOM by recording the photocurrent during surface scanning, further revealing the opto-electrical influences of the nanoparticles. In addition, finite element method simulations have been performed and agree with the results from SNOM. We found the dielectric polystyrene spheres are able to enhance the absorption and benefit the generation of charge carriers in the solar cells.

Semiconductor based light generation is of enormous contemporary interest, given that a large fraction of global energy is used for lighting. White-light semiconductor colloidal quantum dots may find application in future solid state lighting technologies. These dots possess two inherent emission bands, a narrow emissive band attributed to a quantum confined exciton, and a broad emission associated with surface trapping. White light CdSe colloidal semiconductor nanocrystals passivated with phosphonic acids were synthesized by a hot-injection method. Aliquots of this sample are then ligand exchanged with amine and thiol ligands. These samples are embedded in polystyrene films, and a series of temperature dependent photoluminescence measurements are performed. The spectral width as a function of temperature is plotted for all samples. These data are then analyzed in terms of three models. The results suggest that surface line shape broadness may be tied to strong electron-phonon coupling and is largely ligand dependent. The amine and phosphonic acid passivated samples showed large temperature dependence over the range studied, whereas the thiol passivated sample had a lower dependence. This is tentatively explained in terms of hole delocalization in the case of thiol passivation.

The aim of this work is the use of the Z-scan technique to determine the nonlinear refraction and nonlinear absorption of phosphate glass doped with CdS. This glass matrix, termed as PANK (P₂O₅-Al₂O₃-Na₂O-K₂O), was doped with 1, 2 and 3 % of CdS concentration. The quantum dots (QDs) are materials extensively investigated in the last years for their special physical properties associated to discrete energetic levels.

Real-time surface plasmon signal modulation was achieved by electrically varying the pitch of a nanoscale surface relief diffraction grating inscribed on an azobenzene thin film covered with a layer of silver. The azobenzene film was spin coated on an electrostrictive Lead Lanthanum Zirconate Titanate (PLZT) ceramic substrate and AC electric fields were applied longitudinally on the PLZT ceramic causing a change in the grating pitch as well as the surface plasmon resonance wavelength. This method permits extremely accurate control of the surface plasmon wavelength for tunable optics applications.

We report on optoelectronic devices based on novel type of active region - quantum well-dots (QWD) hybrid nanostructures. This hybrid type of the active region can be described as a quantum well, which has an ultradense array of narrow-gap In-rich regions with the size of 20-30 nm, which serve as the localization centers of charge carriers. Such QWD structures can be formed spontaneously during the MOVPE (metalorganic vapor phase epitaxy) deposition of In_xGa_1-xAs (0.3<; x<0.5) on GaAs substrate. Optimal average thickness and composition of In_xGa_1-xAs to achieve maximal PL intensity and photocurrent in QWD structures are determined. Characteristics of edge-emitting lasers based on 5 QWD layers are described. Advantages of using QWD medium in light-emitting and photovoltaic devices are discussed.

The optical analogue to electromagnetically induced transparency (EIT) is modeled for two separate systems with the same formalism and the spectral characteristics together with the generated group delay are compared. First system is a coherently coupled high-Q multi-cavity array which represents the classical EIT and is limited by the finite broadening of the cavity and the second one is a single embedded quantum dot (QD) cavity system, a cavity-QD EIT, that depends on both QD broadening and cavity properties. Similar spectral characters have been observed for both systems but the former generated theoretically two times higher group delays.

An investigation of the optical properties of the multi stacked InAs quantum dot (QD) based photodetectors has been done by changing the capping layer composition and thickness. There is an improvement obtained in the structure and distribution of InGaAs capped QDs than the conventional GaAs capped QDs. It is due to the inhibition of In-Ga intermixing and lesser indium segregation towards the wetting layer in case of InGaAs capping. Here, the combined InGaAs/GaAs capping layer thickness has been varied to investigate the effect of the vertical strain-coupling and QD size distribution. All samples are grown by solid source molecular beam epitaxy with a V/III flux ratio of 50. A variation in InGaAs/GaAs capping layer is done by keeping the total thickness constant at 12 nm, and 18 nm. The ground state photoluminescence emission peak for the 3 nm InGaAs capped QDs have pronounced redshift than the 2 nm InGaAs capped QDs. However, the redshift is more in case of total capping layer thickness of 12 nm (i. e. 36 nm), than the 18 nm capped sample (i. e. 14 nm). It is observed due to better coupling in case of lower capping layer thickness and hence better dot size. Activation energy calculated from the temperature dependent photoluminescence study also gives incremental trend with an increase in coupling (18nm: 163.308meV, and 12nm: 215.53meV), which is attributed to lowering of QD ground state due to change in capping layer thickness. Hence the 12nm capped device with 3nm InGaAs capping gives better results probably due to better strain propagation, and hence better dot distribution.

Epitaxially-grown 10-layer coupled InAs quantum dots with GaAsN/GaAs barrier layers have been investigated. The PL spectra was seen to be a complex convolution of bimodal distribution of QDs along with an asymmetric signature introduced by incorporation of nitrogen into the structures. Reducing the GaAsN/GaAs barrier thickness (from 2/16nm to 2/8nm) resulted in an improvement of PL linewidth as low as 20meV of the dominant PL peak for the sample with thinnest barrier layer. A blueshift in emission was observed due to higher indium intermixing as a result of an increase in overall strain in the multilayer structure. The highly asymmetric exponential tail signature evident from the PL spectra of as-grown samples indicated a higher presence of localized N-induced excitonic states near the conduction band edge. Samples with thicker barriers showed relatively lower asymmetry compared to samples with thinner barriers. Also, samples with thinner barriers showed an arrest in blueshift in the PL spectra with annealing temperature indicating thermal stability.

We demonstrated the ion-sensitive field-effect transistors (IS-FETs) based on nanowires (NWs) with different diameters and doping concentrations to obtain the high sensitivity and various applications. The growth of the catalyst-free InAs NWs was carried out using a horizontal reactor MOCVD system (AIXTRON Inc.). A p-type Si (111) wafer (ρ = 1 -10 Ω-cm) was prepared for the NW growth. Here, NWs with diameters of around 50 ~ 150 nm were grown and the doping concentration also was changed around x±10^16~18 /cm². IS-FETs with the grown InAs NWs were fabricated using the photolithography and the lift-off process. The gas sensing characteristics have been investigated through studying the gate response of the NW conductance in different ambient conditions.

We present here a simple quantum-mechanical model that describes interband optical activity of cubical semiconductor nanocrystals with chiral shape irregularities. Using the developed model, we derive the analytical expression for the rotatory strengths of interband transitions and show that the circular dichroism spectra of the chiral-shape nanocrystal consists only of the electric dipole allowed transitions. Taking into account the splitting of the valence band, one can interpret experimental circular dichroism spectra using just a few fitting parameters. The results of our study may prove useful for various branches of nanophotonics, chiral chemistry, and biomedicine.

InAs nanowires directly integrated on Si platform show great promise in fabricating next generation mid-infrared optoelectronic devices. In this study we demonstrated the growth of catalyst-free, selective-area InAs nanowire arrays on electron beam patterned Si₃N₄/Si(111) by molecular beam epitaxy. Growth parameters were studied, and nanowire growth kinetics dependence on patterned mask opening diameter and interwire distance was investigated. Under certain growth conditions, nanowire diameter was found to be relatively independent of nanohole diameter and pitch. We also realized the growth of randomly-nucleated, self-assembled nanowires on Si(111) and investigated the temperature, flux influence on nanowire morphology.