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Reflectance spectroscopy has been used to determine the refractive indices of nanoscale InxAlyGa1-x-yAs and InxAl1-xAs layers with indium and aluminum concentrations x = 0.21-0.24 and y = 0, 0.1, and 0.2 on specially created Bragg-reflector heterostructures at wavelengths in the range 700-2000 nm. It was demonstrated that the method based on an analysis of the auto- and cross-correlation coefficients of the wavelength derivatives of the dependence of the reflectance of structures of this kind in order to determine the dispersion curves of the materials forming a reflector. It was found that raising the concentration of indium in InGaAs and AlInAs leads to a substantial rise in the refractive index, with a preserved spectral run of the refractive indices, which is characteristic of gallium arsenide and aluminum arsenide. [ABSTRACT FROM AUTHOR]

Abstract: GaAs photovoltaic converters containing quantum well-dot (QWD) heterostructures are studied. The QWD properties are intermediate between those of quantum wells (QWs) and quantum dots. The QWDs are obtained by the epitaxial deposition of In0.4Ga0.6As with a nominal thickness of 8 single layers by metal-organic vapor phase epitaxy. QWDs are a dense array of elastically strained islands that localize carriers in three directions and are formed by a local increase in the indium concentration and/ or InGaAs-layer thickness. There are two quantum-well levels of varied nature in structures with QWDs. These levels are manifested in the spectral characteristics of GaAs photovoltaic converters. A short-wavelength peak with a maximum at around 935 nm is associated with absorption in the residual QW, and the long-wavelength peak (1015-1030 nm) is due to absorption in the QWDs. Investigation by transmission electron microscopy demonstrates that an increase in the number of InGaAs layers leads to stronger elastic stresses, which, in turn, increases the carrier confinement energy in the QWDs and lead to a corresponding long-wavelength shift of the internal quantum efficiency spectrum. [ABSTRACT FROM AUTHOR]

The growth peculiarities of In0.8Ga0.2As quantum dots and their arrays on GaAs surface by metalorganic vapor-phase epitaxy are investigated. The bimodal size distribution of In0.8Ga0.2As quantum dots is established from the photoluminescence spectra recorded at different temperatures. The growth parameters were determined at which the stacking of 20 In0.8Ga0.2As quantum-dot layers in the active area of a GaAs solar cell makes it possible to enhance the photogenerated current by 0.97 and 0.77 mA/cm2 for space and terrestrial solar spectra, respectively, with the high quality of the p-n junction retained. The photogenerated current in a solar cell with quantum dots is higher than in the reference GaAs structure by ~1% with regard to nonradiative-recombination loss originating from stresses induced by the quantum-dot array. [ABSTRACT FROM AUTHOR]

We investigated structural and emission properties of self-organized InP/GaInP quantum dots (QD) grown by metal organic chemical vapor deposition using an amount of deposited In from 7 to 2 monolayers (ML). In the uncapped samples, using atomic force microscopy (AFM), we observed lateral sizes of 100-200 nm, together with a bimodal height distribution having maxima at ∼5 and ∼15 nm, which we denoted as QDs of type A and B, respectively; and reduction of the density of the type-B dots from 4.4 to 1.6 μm-2. The reduction of the density of B-type dots were observed also using transmission electron microscopy of the capped samples. Using single dot low-temperature photoluminescence (PL) spectroscopy we demonstrated effects of Wigner localization for the electrons accumulated in these dots. [ABSTRACT FROM AUTHOR]

The influence of reducing carrier of thermal escape rate with temperature decreasing in various channels on the dark saturation current of a GaAs p–n junction with Ga0.8In0.2As quantum dots has been investigated. The dark saturation current has been calculated for temperatures ranging from 20 to 325 K. The calculation was based on the previously discovered current invariant, which determines the dependence of the saturation current on temperature and bandgap energy. The rates of recombination in various channels and their bandgaps were determined by photoluminescence spectra analysis. For various channels, characteristic temperatures were determined, below which thermal escape rate of carriers is practically absent. The saturation current calculation showed that, despite the change in the rate of recombination in different channels, it is determined only by the recombination in the channel with lower bandgap energy. [ABSTRACT FROM AUTHOR]

The properties of epitaxial GaInP alloys with an ordered arrangement of atoms in the crystal lattice are studied by a number of structural and microscopic methods. The alloys are grown by metal-organic chemical vapor deposition onto single-crystal GaAs(100) substrates. It is shown that, under conditions for the coherent growth of an ordered GaInP alloy on a GaAs(100) substrate, atomic ordering results in radical modifications of the structural properties of the semiconductor compared to the properties of disordered alloys. Among these modifications are a change in the crystal-lattice parameter and, as a consequence, lowering of the crystal symmetry and the formation of two different types of surface nanorelief. With consideration for elastic strains, the parameters of GaInP alloys with ordering as functions of the order parameter are calculated for the first time. It is shown that all experimental data are in good agreement with the developed theoretical concepts. [ABSTRACT FROM AUTHOR]

An anomaly appearing in the photovoltaic characteristics of triple-junction GaInP/GaAs/Ge and of the corresponding double-junction GaInP/GaAs solar cells at ultrahigh concentrations (more than 2000 suns) of incident light has been studied. The light current–voltage characteristics at various concentration ratios of incident light and the dependence of the open-circuit voltage on the photogenerated current were analyzed. It was shown that the anomaly is observed due to the tunnel diode connected back-to-back between the GaInP and GaAs subcells. This diode absorbs photons that pass across the GaInP layers and creates a counter photovoltage. [ABSTRACT FROM AUTHOR]

Injection microlasers with an active region based on arrays of InGaAs/GaAs quantum well-dots, formed by deep etching, have been studied. The manner in which the current–voltage characteristic changes when the diameter microlaser is reduced shows that a nonelectrically conducting layer with thickness of about 1.5 μm is formed near the side surface, which leads to a decrease in the effective current flow area. [ABSTRACT FROM AUTHOR]

We have studied characteristics of a 23-μm-diameter microdisk laser operating in a regime of direct high-frequency modulation at a stabilized heat-sink temperature of 18°C. It is found that the minimum energy consumption in this regime amounts to ~1.6 pJ/bit and is achieved at a modulation frequency of 4.2 GHz. The maximum modulation frequency is 6.7 GHz, at which the minimum energy consumption is 3.3 pJ/bit. [ABSTRACT FROM AUTHOR]

The efficiency of GaInP/GaAs/InxGa1 –xAs triple-junction solar cells obtained by replacing (in the widely used "classical" GaInP/GaAs/Ge heterostructure) the lower germanium with InxGa1 –xAs subcell formed using the metamorphic growth technology has been investigated. Based on an original approach, the optimal indium concentration in the narrow-gap subcell has been found. The main parameters of InxGa1 –xAs subcells with an indium concentration from x= 0.11 to 0.36 were determined and were used to calculate the IV characteristics of GaInP/GaAs/InxGa1 –xAs solar cells. It has been determined that at x= 0.28 the efficiency of the triple-junction solar cell increases by 3.4% (abs.) in comparison with the "classical" solar cell, reaching a value of 40.3% (AM1.5D). Also it has been shown that the efficiency of such solar cells can be increased up to 41%. [ABSTRACT FROM AUTHOR]

The effect of positioning of the In0.8Ga0.2As quantum dots (QDs) array in the i-region of the solar cell (SC) on its photogenerated current and dark saturation currents, which determine the device operating voltage, have been investigated. It was found out that the indicated photoelectric characteristics depend on the location of the QD array relative to the electric field of the p–n junction. The displacement of the QD array to the boundary of the weakly doped base leads to a decrease in the photogenerated current. But at the same time, the voltage drop effect, which is well-known for nanoheterostructural SC, is minimal. [ABSTRACT FROM AUTHOR]

Spectral characteristics of the Ge subcell of triple-junction GaInP/GaAs/Ge solar cells have been simulated. It was shown that using a GaInP nucleation layer that creates a shallow diffusion p-n junction in Ge can raise the photogeneration current of the Ge subcell by ~4.5 mA/cm2 as compared with the value in the case of a GaAs nucleation layer. The optimal thickness of the GaInP layer (170-180 nm) makes it possible to additionally raise the photocurrent by ~1.5 mA/cm2. It was experimentally demonstrated that the photogenerated current of the Ge subcell of GaInP/GaAs/Ge solar cells increases by 3.9 mA/cm2 on replacing the GaAs nucleation layer with GaInP and there is an additional gain by 0.9 mA/cm2 on using the optimal thickness of the GaInP nucleation layer. [ABSTRACT FROM AUTHOR]

Results are presented of a study of light-current characteristics and far-field patterns of emission of stripe lasers with coupled planar waveguides. This configuration makes it possible to suppress the generation of excited modes and to have a small (about 0.9 μm) depth of the active region from the surface of the laser crystal. A high-temperature stability of the angular emission divergence (34.0° ± 1.5°) in the temperature range 20-80°C is demonstrated. The largest value of the output power is limited to 12.2 W in the continuous-wave mode by the catastrophic mirror damage. [ABSTRACT FROM AUTHOR]

The method of scanning Kelvin-probe microscopy is used to show that the effect of triboelectrification is observed when the tip of an atomic-force microscope interacts with the surface of n-GaAs epitaxial layers. The sign of the change in the potential indicates that the sample surface after triboelectrification becomes more negative. The observed specific features of the phenomena can be attributed to the thermally activated generation of point defects in the vicinity of the sample surface due to deformation caused by the tip. [ABSTRACT FROM AUTHOR]

Developed and investigated are IR (850 nm) light-emitting diodes based on AlGaAs/Ga(In)As heterostractures grown by the MOCVD technique with multiple quantum wells in the active region and with a double optical reflector consisted of a multilayer Al0.9Ga0.1As/Al0.1Ga0.9As Bragg heterostructure and an Ag mirror layer. Light-emitting diodes with the external quantum efficiency EQE = 37.5% at current densities greater than >10 A/cm2 have been fabricated. [ABSTRACT FROM AUTHOR]

We report on InGaAs/GaAs quantum dot injection microdisk lasers laterally connected with a bus waveguide fabricated by planar technology from the same epi-structure. Various coupling schemes of microlaser with waveguide are studied including a microlaser attached to a waveguide (zero gap), a 100 nm gap for evanescence light outcoupling, and with a waveguide surrounding the resonator. The modes outcoupling and microlaser's loss (Q-factor) are analyzed by simulation of the lasers. A strong decrease in the number of the microdisk resonance lines associated with an increase in loss in the resonator due to the coupling with waveguide is observed in modeling and experimentally. We study the spectral and lasing parameters of the microdisk lasers, as well as characteristics of the outcoupled emission, and demonstrate efficient light outcoupling for 30 and 40 μm diameter continuous wave operating microdisk laser up to 96 °C. [ABSTRACT FROM AUTHOR]

IR light-emitting diodes (LEDs) based on InGaAs/AlGaAs multiple quantum wells (MQWs) and AlxGa AsyP layers, compensating stress in the active area, have been developed. The optical losses caused by absorption of the radiation generated by the active area (λ = 940 nm) have been investigated at different doping levels of n-GaAs substrates. It is shown that reduction of the donor doping level from 4 × 1018 to 5 × 1017 cm–3 gives an increase in the LED quantum efficiency of ~30%. A technology making it possible type to eliminate completely the optical losses caused by absorption during radiation output has been developed. Removal of the substrate and transfer of the device structure to a carrier substrate with formation of a rear metal reflector made it possible to create LEDs demonstrating a twofold increase in the external quantum efficiency (EQE) and efficiency (~40%) as compared to the technology of radiation output through an n-GaAs substrate. [ABSTRACT FROM AUTHOR]

Grown by metalorganic vapour phase epitaxy (MOVPE) InxGa1-xAs metamorphic laser power converters have been considered. Metamorphic buffer designs with high quality top layers have been developed. Photovoltaic converters with In0.24Ga0.76As photoactive area and optimised buffer have demonstrated efficiency 41.4% for 1064 nm monochromatic radiation conversion and ~40% for laser power conversion. [ABSTRACT FROM AUTHOR]

We consider a high-efficiency photovoltaic module optimized for conversion of monochromatic radiation with a wavelength of 809–850 nm. The module includes four photovoltaic converters with a total area of 16 cm2, which operate with laser radiation of a power higher than 1 W and ensure a working voltage higher than 4 V. In the development and obtaining AlGaAs/GaAs structures for receiver-converters of radiation, we have used the method of epitaxy from the liquid phase and the method of metalorganic vapour-phase epitaxy. When the photovoltaic module operates in the regime of uniform irradiation of the light-detecting surface, the efficiency of conversion of a high-power (6.2 W) laser radiation exceeds 60%. [ABSTRACT FROM AUTHOR]

The electroluminescence spectra and the dependences of the open circuit voltage on the photogenerated current are studied for GaAs solar cells the p–n junction of which contained various numbers of rows (r) of quantum objects based on In0.4Ga0.6As layers. For all samples, the saturation current (J0), the band gap of the quantum object (), and the open circuit voltage drop (ΔVoc) relative to the reference (r = 0) sample are obtained. A model adequately describing the dependences J0(r) and ΔVoc(r) is proposed, and the model parameters are found, including the current invariant Jz = 1.4 × 105 A/cm2, which uniquely relates the saturation current to the band gap of the quantum object. [ABSTRACT FROM AUTHOR]

The current–voltage characteristics of InxGa1 –xAs/GaAs metamorphic photovoltaic converters with built-in n-InGaAs/InAlAs Bragg reflectors are studied at an indium content of x = 0.025–0.24. The series resistance of the heterostructures is measured in the temperature range from 90 to 400 K. It is found that a sharp rise in the resistance of silicon-doped reflectors with an increasing fraction of In is due to weak activation of the donor impurity in InAlAs–n:Si layers. As a result, the energy barriers for majority carriers are formed in the latter, with a height of 0.32–0.36 eV and a substantial width. To suppress this effect, the technology of the Te doping of n-InGaAs/InAlAs Bragg reflectors is developed, which reduces the series resistance by five orders of magnitude. This makes it possible to keep the fill factor of the current–voltage characteristic above 80% up to current densities of 2 A/cm2. Values exceeding 85%, achieved for the quantum efficiency, indicate that the "memory" and tellurium segregation effects characteristic of this kind of impurity are suppressed. [ABSTRACT FROM AUTHOR]