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High-speed photodetectors (PDs) based on InGaAs/GaAs quantum well-dot (QWD) nanostructures with the frontal-end and back-end input of radiation have been studied. A PD with 40 rows of QWDs exhibited a spectral responsivity of up to 0.4 A/W in the 950–1100 nm optical range at a –5-V bias voltage. The decay time constant of pulsed response for PDs with an input area of 1.4 × 10–4 cm2 was ~250 ps.

InAs and In0.8Ga0.2As quantum dots in a GaAs matrix as well as GaAs solar cells with quantum dots of both types in the i-region are obtained by metalorganic vapor-phase epitaxy. As a result of investigations by photoluminescence and transmission electron microscopy, it is found that the In0.8Ga0.2As quantum-dot array is highly uniform, contains a smaller number of large imperfect quantum dots, and also provides a decrease in mechanical stresses in the structure. An analysis of the spectral dependences of the internal quantum yield shows that the quality of a solar-cell matrix after embedding up to 20 rows of In0.8Ga0.2As quantum dots remains at a level close to the reference GaAs solar cells. In this case, a linear increase in the additional photocurrent generated due to the absorption of sub-bandgap photons in In0.8Ga0.2As quantum dots is provided with an increase in the number of rows of quantum dots, since the value of the photocurrent gain per row is preserved.

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.

Results are reported of using subcontact layers with energy gap width Eg of 0.35 to 0.8 eV for obtaining low-resistivity electrical contacts to p-InP. An experimental dependence of the contact resistance on Eg of the subcontact material InxGa1 – xAs was obtained.

Site-controlled growth of InP/GaInP2 quantum dots has been demonstrated by means of selective epitaxy technique realized with a SiO2 mask and e-beam lithography. Critical influence of the growth temperature on QD formation in the selective epitaxy has been demonstrated. Role of SiO2 deposition technique on the selective epitaxy of QD’s has been established.

The topic of the work is laser power converters (LPCs) for wavelength range of λ=1 – 1.1 µm based on metamorphic InGaAs heterostructures. Variation of the indium concentration “x” in the InxGa1-xAs active area from 0.23 to 0.18 and the use of a distributed Bragg reflector have been investigated. As a result of the voltage increase (due to the minimum concentration of indium in a LPC with indium concentration of about 18% in the active region), the following record efficiency (for such a type of LPC) for monochromatic light conversion has been achieved: about 52% at 1.06 µm and 55% at 1.02 µm. Moreover, the use of a Bragg reflector has allowed stabilizing high spectral response at the InGaAs absorption edge (x=0.18), and demonstrating more than 47% efficiency at a real operating temperature range (higher than +50°C) at 1.06 µm.

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.

Metamorphic Ga0.76In0.24As heterostructures for photovoltaic converters are grown by the MOCVD (metal–organic chemical vapor deposition) technique. It is found that, due to the valence-band offset at the p-In0.24Al0.76As/p-In0.24Ga0.76As (wide-gap window/emitter) heterointerface, a potential barrier for holes arises as a result of a low carrier concentration in the wide-gap material. The use of an InAlGaAs solid solution with an Al content lower than 40% makes it possible to raise the hole concentration in the widegap window up ~9 × 1018 cm–3 and completely remove the potential barrier, thereby reducing the series resistance of the device. The parameters of an GaInAs metamorphic buffer layer with a stepwise In content profile are calculated and its epitaxial growth conditions are optimized, which improves carrier collection from the n-GaInAs base region and provides a quantum efficiency of 83% at a wavelength of 1064 nm. Optimization of the metamorphic heterostructure of the photovoltaic converter results in that its conversion efficiency for laser light with a wavelength of 1064 nm is 38.5%.

The topic of the work is the metamorphic InGaAs heterostructure for laser power converters with λ=1064 nm. The problem of conversion efficiency under various conditions of incident radiation is investigated: with uniform illumination with a Xe-lamp, with a continuous high-power laser, and with a pulsed laser. The thermal coefficient α=ΔV/ΔT of overheating is calculated for continuous laser. An increasing contribution of resistive losses, associated with the spreading resistance, for a focused laser beam (when the focus spot is smaller than the photoactive area of a sample) is discussed. It has been demonstrated that with a unfocused laser beam (the mode corresponding to the practical case of wireless energy transmission), the conversion efficiency of laser radiation is compared with the efficiency under a Xe-lamp. For laser power converters with optimal (according to calculated from spectral characteristics MCC diffusion length) thickness, the efficiency of more than 48% (λ=1064 nm) within 1.3–13 W/cm2 incident power was demonstrated with 50.6% maximum at 5.2 W/cm2.

Research into the formation of InAs quantum dots (QDs) in GaAs using the metalorganic vapor phase epitaxy technique ispresented. This technique is deemed to be cheaper than the more often used and studied molecular beam epitaxy. The bestconditions for obtaining a high photoluminescence response, indicating a good material quality, have been found among awide range of possibilities. Solar cells with an excellent quantum ef?ciency have been obtained, with a sub-bandgapphoto-response of 0.07 mA/cm2per QD layer, the highest achieved so far with the InAs/GaAs system, proving the potentialof this technology to be able to increase the ef?ciency of lattice-matched multi-junction solar cells and contributing to abetter understanding of QD technology toward the achievement of practical intermediate-band solar cells.

Heterostructures of metamorphic GaInAs photovoltaic converters (PVCs) are on GaAs substrates by the metal-organic chemical vapor deposition (MOCVD) method. It is shown that using a multilayer metamorphic buffer with a step of 2.5% in indium content and layer thicknesses of 120 nm provides the high quality of bulk layers subsequently grown on the buffer up to an indium content of 24%. PVCs with a long-wavelength photosensitivity edge up to 1300 nm and a quantum efficiency of ~80% in the spectral range 1050–1100 nm are fabricated. Analysis of the open-circuit voltage of the PVCs and diffusion lengths of minority carriers in the layers demonstrates that the density of misfit dislocations penetrating into the bulk layers increases at an indium content exceeding 10%.

In the work the effect of the number of In0.8Ga0.2As stacked quantum dots (QDs) embedded in a single-junction GaAs solar cell (SC) on its photoelectric characteristics has been studied. A series of GaAs SC structures, which differed by a number of embedded QD layers, were grown using metalorganic vapor phase epitaxy. By analyzing the electroluminescence spectra and the current–voltage characteristics of the obtained structures the main reason for the voltage loss in SC with QDs has been established which is an increase in recombination through the QD levels with an increase the number of QD layers.

The results of studying the InxGa1−xAs laser power converters with the indium percentage of 18% and of 23% are presented. In the mode of 1064 nm laser radiation conversion the photovoltaic parameters dynamics with raising temperature is discussed.

Laser power converters (LPCs) based on InxGa1-xAs/GaAs metamorphic heterostructure grown by MOVPE have been investigated. Both direct study of transmission electron microscopy images and analysis of the dark I–V curves at a low photogenerated current have shown the absence of the effect of threading dislocations from the metamorphic buffer on the LPC parameters. It has been shown, according to the “voltage” and “current” invariants that voltage loss in all investigated LPCs evidences the good quality of p-n junctions for the operating mode of high power laser radiation conversion. It has been also demonstrated that the method of saturation current approximation with current invariant allows obtaining the limit voltage losses irrespective of photogenerated current. Band-gap and thickness of the InGaAs LPCs have been adjusted using spectral characteristics. Fundamental losses (thermal and resistive) and ways to minimize them have been discussed. As a result, LPCs based on In0.23Ga0.77As have demonstrated the laser conversion efficiency (λ = 1064 nm) of more than 50% with maintaining the efficiency of more than 48% up to 13 W/cm2.

The fundamental reason for the decrease in solar cells (SC) voltage when introducing nanostructures has been found. It consists in the fact that recombination redistributes between nanostructures and bulk GaAs. It has been shown that, by changing the position of nanostructures medium in the p-i-n GaAs SCs, it is possible to partially suppress the recombination and improve the voltage maintaining an increase in the short-circuit current. The decrease of the recombination via nanostructures has provided an increase in SC efficiency from 19.87% to 21.94%.

The specific features of growth in the InAs-GaAs system by the metal-organic chemical vapor deposition method are studied. The dependences of the In content of the InxGa1 − xAs solid solution and of the InAs growth rate on the molar flow of In in a wide temperature range (480–700°C) are determined. The growth processes of InAs quantum dots (QDs) on GaAs with different surface misorientations are examined. The conditions are found in which InAs QDs are formed with a small number of defects and at a high density on a GaAs “sublayer” grown at a high rate. An epitaxial technique is developed for the synthesis of InAs QDs with multimodal size distribution and an extended photoluminescence spectrum, which can be effectively used in designing solar cells with QDs in the active region.

The MOVPE growth of InP/GaInP quantum dots (QDs) on GaAs substrate “defects” formed by a focused beam of Ga+ ions is studied. It is shown that ordered arrays of QDs with a density of 0.25 (μm)−2 can be obtained in the InP/GaInP system. It is demonstrated that effective luminescence can be obtained by using two QD sheets separated by a GaAs/GaInP buffer layer.

The topic of the work is the metamorphic InGaAs heterostructures for laser power converters (LPC) and their performance at different measurement conditions. Three different illumination conditions were studied: monochromatic Xe-lamp uniform illumination, laser with quasi-uniform illumination (with laser beam unfocusing) and non-uniform focused laser illumination. For simulating the experimental IV-curves as well as FF-Jg, Voc-Jg and η-Jg dependences, a tube model developed earlier and describing the charge carrier transport along current lines was used for all three illumination regimes. In the absence of losses (Xe-lamp and unfocused laser), the perfect model simulation model exhibiting an experimental efficiency greater than 50% (for λ=1064nm) has been demonstrated. As a result of simulation of LPC characteristics obtained under focused laser illumination, the losses associated with uniform light distribution as well as with an additional resistance, which decrease the LPC efficiency, have been found.

In this work, the study of formation regimes of In0.8Ga0.2As quantum dots on GaAs surface by metallorganic vapour-phase epitaxy has been carried out. The influence of post-growth interruption after the quantum dots deposition on the optical and physical properties of the formed objects has been investigated. It has been established that the interruption time of 2-5 seconds is optimal for the In0.8Ga0.2As/GaAs material system and growth conditions. For the chosen interruption time, the quality of formed quantum dots and their physical sizes were estimated using transmission electron microscopy: lateral size is 10 – 20 nm, height is not exceeding 5 nm and concentration is ∼9.8·1010 cm−2.

Triple-junction solar cells InGaP/GaAs/Ge usually are manufactured using MOCVD technology. However, the potential of such structures is investigated in the laboratory on samples made using MBE. One of the ways to increase efficiency is the implanting of InAs quantum dots in GaAs cascade. In this paper the approaches to the mathematical modeling of Ga (In) As structures grown by MOCVD and MBE are studied.

Resistance-less dark IV-curves of GaAs solar cells with and without quantum-dimensional objects allied to both quantum dot and quantum well have been obtained and analyzed. Anomalous large increase of the pre-exponential factors was observed in tested (with quantum objects) p-n junctions. According to proposed interpretation embedding of quantum objects in p-n junction created new current flow mechanisms. As a result current flows throught recombination transitions inside quantum objects in space charge region of p-n junction.

In the triple-junction InGaP/Ga(In)As/Ge solar cells there is an unused potential for increasing efficiency. The photocurrent of the lower (Ge) subcell greatly exceeds the photocurrents of the middle (GaAs) and upper (GaInP) subcells. It leads to recombination losses in the lower subcell. Integration of quantum dots arrays into the middle subcell allows improving the balance of photocurrents. It potentially allows increasing the efficiency of the device. Practical and theoretical studies in this paper allow to establish the optimal design of the quantum dots array providing the balance of photocurrents in InGaP/Ga(In)As/Ge solar cell.

Development of Metalorganic Vapor Phase Epitaxy (MOVPE) technology of InAs quantum dots (QDs) in GaAs for photovoltaic applications is presented. The growth peculiarities in InAs-GaAs lattice-mismatched system were considered. The photoluminescence (PL) intensity dependences on different growth parameters were obtained. The multimodal distribution of QDs by sizes was found using AFM and PL methods. GaAs solar cell nanoheterostructures with imbedded QD arrays were designed and obtained. Ones have been demonstrated a significant increase of quantum efficiency and photogenerated current of QD solar cells due to photo effect in InAs QD array (0.59 mA/cm2 for AM1.5D and 82 mA/cm2 for AM0).

Metamorphic heterostructure photoconverters (PC) based on InGaAs have been grown on GaAs substrates by the MOCVD technique. It has been shown that using the multilayer metamorphic buffer with layer thickness of 120 nm and In composition step of 2.5% provides a good quality of the bulk layers grown on the buffer with up to 24% of In. A PC with photosensitivity up to 1350 nm and the quantum efficiency of 80% in the range of 1050-1100 nm have been made. The 34.5% efficiency of laser radiation conversion at 1064 nm has been demonstrated.