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—Studies have been carried out and a technology has been developed for the formation of a separating mesa structure in fabrication of multi-junction solar cells based on the GaInP/GaInAs/Ge heterostructure. Methods for etching of the heterostructure layers have been studied: wet chemical etching in compositions based on HBr, K2Cr2O7, and H2O and the plasmachemical etching in a flow of the BCl3 working gas. A comparative analysis of the etching methods was made. Protective masks based on a photoresist layer and TiOx/SiO2 were developed. Multi-junction solar cells with low leakage current (less than 10–7 A at a voltage of 0.5–1 V) were fabricated.

We have studied the dynamics of air humidity in the interior of a concentrator photovoltaic (CPV) module equipped with air-drying device filled with moisture-absorbing material based on silica gel. A new design of the air-drying device was developed for preventing the deposition of condensate onto the surfaces of a Fresnel lens, solar cell, and CPV module. Under unfavorable ambient conditions (relative humidity up to 95%), this device allowed to reduce the inner humidity to 25–55% at cyclic temperature variation within 15–45°C and to increase the dew point deficit up to 10–25°C.

Development of lift-off technique of AlGaAs/GaAs- heterostructures, grown by the Metalorganic vapour-phase epitaxy, to GaAs carrier-substrate using silver-containing paste or Au-In compound has been carried out. Forming process of frontal ohmic contact to GaAs n-type conductivity based on contact systems Au(Ge)/Ni/Au and Pd/Ge/Au with specific contact resistance (2-5)·10-6 Ω·cm2 has been investigated. Analyzed was the influence of heterostructure lift-off technique and forming process of frontal ohmic contact on the IR light-emitting diodes parameters: minimum light-emitting diodes (1 mm2 square) series resistance was 0.16 Ω. Optical power 270 mW at current 1.5 A has been achieved. Keywords: AlGaAs/GaAs- heterostructure, light-emitting diode, transfer to carrier-substrate, Au--In- compound, ohmic contacts.

The determination of optical coefficients of absorbing coatings in the far infrared spectrum on silicon substrates is considered in this paper. To find them, a technique is used based on taking into account correction associated with absorption spectra. Correction of the spectra is carried out by exploitation models of the absorbing film. Optical coefficients of BaYF5 films in the spectrum region of 1.3-27 microns were obtained. On their basis, a band-pass metal-dielectric filter was synthesized for a wavelength 5 micron.

Methods for passivation and protection of p–n junctions at places of their emergence at the lateral surface of a mesa structure and for sealing-off of multijunction solar cells based on a GaInP/GaAs/Ge structure have been studied. Protective coatings based on silicon nitride and silicone layers were examined by analyzing dark current–voltage characteristics of the solar cells. The distribution of the electroluminescence was analyzed.

High-efficiency concentrator photovoltaic modules have been developed and fabricated. The modules include a lens panel based on 32 Fresnel lenses (12 × 12 cm each), 32 multi-junction solar cells with secondary concentrators in the form of phocons, and heat-removing electrically insulating boards based on an aluminum oxide ceramic placed on the backside aluminum base. Efficiency measurements of a 0.46-m2 module under a pulsed sunlight simulator (AM1.5D, 1000 W/m2) yielded a value of 32.3%. An efficiency of 33.9% was obtained for a subunit with an area of 144 cm2.

The power generation of the phtovoltaic installations depends on the concentration modules’ efficiency and the Sun tracking accuracy. We have developed a system for monitoring instant tracking accuracy based on a recorder and a projecting system of solar disk imaging.

The results of studies of characteristics of heat-removing electrical insulating plates of different designs based on heat-conducting AlN and Al2O3 ceramics and aluminum-oxide plates based on aluminum plates are presented. Thermophysical parameters of the heat-removing plates were assessed by measuring the temperature of p–n junctions of the photoelectric converters mounted on the plates with thermal load applied to them. It was found that the minimum overheating temperature of p–n junctions, 45°C, was observed at the supplied thermal power of 13 W, when the photoelectric converters were installed on the AlN ceramics. In photoelectric converters installed on the Al2O3 ceramics, the overheating of p–n junctions was 49°C, while it reached 70°C on the aluminum-oxide substrate.

Spectral characteristics of the Ga(In)As subcell of triple-junction GaInP/Ga(In)As/Ge solar cells have been experimentally and theoretically studied. It is established that the use of a wide-bandgap “window” layer with optimum thickness (100 nm for Ga0.51In0.49P, 110 nm for Al0.4Ga0.6As, and 115 nm for the Al0.8Ga0.2As) in Ga(In)As subcell allows the response photocurrent to be increased by about 0.5 mA/cm2; the change of material in the rear potential barrier of the GaInP subcell from Al0.53In0.47P to p+-Ga0.51In0.49P or AlGaAs allows the short-circuit current of Ga(In)As subcell to be additionally increased by about 0.8 mA/cm2; and the use of a wide-bandgap n++-Ga0.51In0.49P layer instead of n++-GaAs in the tunnel diode increases the photocurrent by about 1 mA/cm2.

Electrical supply sources based on photovoltaic converters and tritium radioluminescent lamps with blue and green glow are developed and fabricated. AlxGa1 –xAs/n-GaAs p–n heterostructures with various band-gap widths (Eg = 1.4–1.9 eV) and compositions of the active region (x = 0.1–0.35) are prepared by low-temperature liquid-phase epitaxy. The photovoltaic converter with an area of S = 0.12 cm2 upon irradiation by a green tritium lamp (wavelength λ = 550 nm) has the short-circuit current density 180 nA/cm2 and output electrical power >100 nW/cm2.

Photovoltaic characteristics of heterostructure AlxGa1 – xAs/GaAs p–i–n photodiodes fabricated by molecular-beam epitaxy have been studied. Efficiencies of 50% were reached in conversion of monochromatic light in the photovoltaic mode at power density of up to 200 W/cm2 at a wavelength λ = 830 nm. A relationship was demonstrated between the “saturation currents” for the diffusion-related charge-transport mechanism (Shockley) in p–i–n photodiodes, calculated from dark current–voltage characteristics, and the experimental values of efficiency. As the “saturation current” of the diffusion-related charge-transport mechanism increases by an order of magnitude, a relative decrease in the efficiency from the maximum value by more than 10% is observed under excitation by constant or pulsed monochromatic light.

A multilayer system of ohmic contacts for GaAs/AlGaAs photovoltaic converters has been developed. A method of ohmic contact blackening is suggested with the aim of improving the coefficient of optical signal reflection from an Ag/Au/Ag multilayer contact. Owing to blackening, the reflection coefficient has been decreased more than tenfold.

Multi-junction solar cells based on III–V compounds are the most efficient converters of solar energy to electricity and are widely used in space solar arrays and terrestrial photovoltaic modules with sunlight concentrators. All modern high-efficiency III–V solar cells are based on the long-developed triple-junction III–V GaInP/GaInAs/Ge heterostructure and have an almost limiting efficiency for a given architecture — 30 and 41.6% for space and terrestrial concentrated radiations, respectively. Currently, an increase in efficiency is achieved by converting from the 3-junction to the more efficient 4-, 5-, and even 6-junction III–V architectures: growth technologies and methods of post-growth treatment of structures have been developed, new materials with optimal bandgaps have been designed, and crystallographic parameters have been improved. In this review, we consider recent achievements and prospects for the main directions of research and improvement of architectures, technologies, and materials used in laboratories to develop solar cells with the best conversion efficiency: 35.8% for space, 38.8% for terrestrial, and 46.1% for concentrated sunlight. It is supposed that by 2020, the efficiency will approach 40% for direct space radiation and 50% for concentrated terrestrial solar radiation. This review considers the architecture and technologies of solar cells with record-breaking efficiency for terrestrial and space applications. It should be noted that in terrestrial power plants, the use of III–V SCs is economically advantageous in systems with sunlight concentrators.

The postgrowth processing of mesa structures for multijunction solar cells based on GaInP/GaInAs/Ge heterostructure has been studied. Methods of wet chemical and electrochemical etching are considered, and a technology of forming a separation mesa structure is proposed that ensures improved surface quality and profile of the side wall of a mesa for heterostructures with various compositions of layers.

The results of the development of a radioisotope power supply source based on a semiconductor (AlxGa1 –xAs/GaAs) β-radiation energy converter and tritium as a radiation source are presented. The efficiency of this converter with a tritium saturated titanium disk, a green luminescent tritium lamp, or tritium gas as a radioisotope radiation source is compared. For a converter based on the Al0.35Ga0.65As/GaAs heterostructure in a capsule with tritium, efficiency η = 5.9% at a maximum specific output electrical power of 0.56 μW/cm2. Due to their long service life, such stand-alone and compact power supply sources can be used in space and subsea technologies, implantable cardiac pacemakers, biosensors, and portable equipment of high reliability.

The formation of antireflection coating on multijunction solar cells based on A3B5 semiconductor heterostructures has been studied at the stage of structure surface processing by methods of plasmachemical, wet chemical, and ion-beam etching. A technology of creating antireflection coatings based on TiOx/SiO2 layers is developed. The obtained coatings are characterized by improved adhesion to the surface of heterostructure and reduced reflection coefficient of multijunction solar cells.

Hybrid solar cells based on InGaP/Ga(In)As/Ge multijunction structures integrated into crystalline Si heat-removal base and provided with sunlight concentrator system based on linear Fresnel lenses and carboplastic mount structure have been developed and investigated. The hybrid solar cells with sunlight concentrators in the photovoltaic module provide a specific electric power of 390 W/m2 (AM0, 1367 W/m2) at a photoconverter unit specific weight reduced to 1.0 kg/m2. Improved photovoltaic characteristics and high radiation resistance allow using the proposed hybrid solar modules with sunlight concentrators in space solar batteries and autonomous power supply facilities.

Ohmic contacts of power AlGaAs/GaAs-based photovoltaic converters were studied, and a technique for their fabrication was developed. Effect of the doping level of the contact layer on the free-carrier density and the contact resistivity was examined. A technique for fabrication of 2- to 4-μm-thick ohmic contacts with electrochemical deposition of gold layers was studied. The effect of deposition modes on the surface morphology of ohmic contacts and their solidity and conductivity was revealed.

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.

The influence exerted by the heat removal conditions on the extent of overheating of photovoltaic converters of high-power (>103 W/cm2) laser light has been studied. The temperature of the p–n junction of photovoltaic cells was measured by recording the instantaneous values of the open-circuit voltage generated by laser light. The effect of cooling in high-efficiency photovoltaic cells (efficiency = 55%) via removal of a substantial part of absorbed optical power by the photocurrent into the external load was demonstrated. It was shown that, at laser radiation power of 2.5 W, the overheating of a photocell with an area of 1.7 × 10–3 cm2 relative to the copper heatsink temperature is 48°C in the no-load conditions and 30°C in operation with the optimal load.

High-efficiency photovoltaic converters (PVCs) have been developed and fabricated by liquidphase epitaxy in the AlGaAs–GaAs system with laser light (λ = 850 nm) introduced through the edge surface in parallel to the plane of the p–n junction of the device structure. To raise the efficiency of light “capture” by the p–n junction, an AlxGa1–xAs waveguide layer is formed, in which the content of aluminum gradually varies from x = 0.55 to 0.15 so that the refractive index gradient is created in this layer and light beams are diverted toward the p–n junction. When a PVC (having no antireflection coating) is exposed to 0.1- to 0.2-W laser light, an efficiency of 41.5% is obtained. Depositing an antireflection coating on the edge surface of a PVC raises its efficiency to 55%.

This study is aimed at investigating the main photoelectric characteristics of three-cascade InGaP/InGaAs/Ge photoelectric converters in a broad temperature range (–197°C ≤ T ≤ +85°C). On account of analysis of photosensitivity spectra and optical current–voltage characteristics, such temperature dependences as the open-circuit voltage (V oc), filling factor of the current–voltage characteristic (FF), and the photoelectric conversion efficiency of solar radiation are determined. Investigations are performed at illumination intensities corresponding to operation under concentrated radiation. Decreased temperatures facilitate the selection of samples with the minimal “parasitic” potential barriers. The influence of excitationtransfer processes from a cascade into a cascade is estimated by means of secondary luminescent radiation. The highest photoelectric conversion efficiency of 52% is measured at a concentration multiplicity of 100 “suns” and a temperature of–160°C.

Photovoltaic converters of laser light with a wavelength of λ = 1550 nm are developed using liquidphase epitaxy (LPE), metal-organic chemical-vapor deposition (MOCVD), and diffusion from the gas phase into the n-GaSb substrate. Photocells with an area of S of 4, 12.2, and 100 mm2 are fabricated and tested. The characteristics of the samples produced by different methods are compared. The monochromatic efficiency is found to be 38.7% for the best converters (with S = 12.2 mm2) at a laser power of 1.4 W.

Photovoltaic laser-power converters for a wavelength of λ = 809 nm are developed and fabricated on the basis of single-junction AlGaAs/GaAs structures grown by metal-organic vapor-phase epitaxy. The parameters of the photovoltaic structure constituted by an optical “window” and a cladding layer are optimized by mathematical simulation. Photovoltaic converters with areas of S = 10.2 and 12.2 mm2 and 4 cm2 are fabricated and studied. For photocells with S = 10.2 mm2, the monochromatic efficiency (η) was 60% at a current density of 5.9 A/cm2. A photovoltaic module with a working voltage of 4 V (η = 56.3% at 0.34 A/cm2) is assembled.

The paper proposes an experimental approach to determine the external quantum efficiency of multijunction solar cells with pronounced optical coupling. A new technique based on the cascade mechanism of coupling has been elaborated to separate the influence of the induced luminescent flux from the external illumination and to establish the absolute values of photosensitivity without negative impact of optical interaction between subcells. The novelty of this work lies in the method extended to multijunction devices with N-number of subcells.

Edge illuminated laser power PV converters of near-IR region (800-850nm) were made by liquid phase epitaxy. The developed converters are based on the GaAs active region with a wide (50-100 µm) AlGaAs waveguide layer. Gradient Al content in the waveguide layer ensured effective light collection on the p-n junction. Methods of device characterization based on high spatial resolution optical techniques were developed. Efficiency of 41.5% (no ARC applied) of laser power (850nm) conversion has been demonstrated at light power density of 8kW/cm2.

Results obtained in the development of a metal-organic vapor-phase epitaxy (MOVPE) technology and in studies of the electrical parameters of photovoltaic converters based on heterostructures in the InP/InGaAsP system for the spectral range 0.95–1.2 μm are presented. A MOVPE technique is developed for obtaining and doping InGaAsP solid solutions around the spinodal dissociation region with a band-gap width of about 1.0 eV. Photovoltaic converters of 1000-× concentrated sunlight are fabricated.

New-generation concentrator modules use III–V nanoheterostructure cascade solar cells the efficiency of which can be raised to 50% for the number of cascades exceeding three. To obtain a high overall efficiency of photovoltaic conversion in power plants and extend their service time, it is necessary that the design of the modules be optimal in terms of optics and thermal engineering. In this work, main challenges in designing solar modules, such as optical concentration of radiation and residual heat removal, are considered. The results of pilot works that have been recently done in the Ioffe Physical Technical Institute are primarily reported.

The photoelectric characteristics of triple-junction InGaP/Ga(In)As/Ge solar cells are studied in relation to the method used to form the photocell chip. It is shown that the application of a postgrowth technique developed in the study for separating a nanoheterostructure into chips in a single process makes it possible to improve the quality of passivation of the chip edges, which diminishes the surface leakage currents and makes larger the yield of devices with improved characteristics.

A correlation between the main parameter of a solar cell, the conversion efficiency, and its dark I–V characteristic is investigated. A formula is derived that expresses an increment (decrement) of the efficiency through a decrement (increment) of the current measured at a certain voltage (here at 2.4 V). Relationships are deduced based on which six methods for passivating the sidewalls of triple-junction InGaP/GaAs/Ge heterostructures grown by metal-organic vapor-phase epitaxy are tested to see how they influence the dark I–V characteristic. The influence of different factors, such as post-growth annealing, damaging radiation, etc., on the solar cell efficiency can be estimated by taking the dark I–V characteristic.

A new model of connecting elements for monolithic multijunction solar cells based on III–V compounds is proposed, in which p-n junctions with crystalline inclusions of a foreign semiconductor material in the space-charge region are used instead of p++-n++ tunnel junctions. The study shows that the introduction of crystalline inclusions to the space-charge region of the p-n junction in a GaSb-based structure allows current densities of ∼50 A/cm2 at an ohmic loss of ∼0.01 Ω cm2. The obtained characteristics of the connecting elements with crystalline inclusions show their applicability to multijunction solar cells for concentrated light conversion.

The parameters of the concentrating photoelectric modules with triple-junction (InGaP/GaAs/Ge) solar cells whose focusing system contains an original secondary optical element are studied. The element consists of a plane-convex lens in optical contact with the front surface of an intermediate glass plate and a cylindrical waveguide that is located on the rear side of the glass plate above the surface of the solar element. It is demonstrated that the structure of the secondary optical element provides a wide misorientation characteristic of the concentrator and the cylindrical waveguide allows a more uniform radiation density over the surface of the solar cell. The effect of chromatic aberration in the primary and secondary optical systems on the parameters of photoelectric modules is analyzed. It is demonstrated that the presence of waveguides with a length of 3–5 mm leads to effective redistribution of radiation over the surface of the solar cell whereas shorter and longer waveguides provide the local concentration of radiation at the center of the photodetecting area.

High-current solar cells based on gallium antimonide and intended for use in solar modules and systems with solar-spectrum splitting at large solar light concentration ratios, in thermophotovoltaic generators with a high-temperature emitter, and in laser energy converters have been designed and fabricated by the diffusion of zinc from the gas phase. The influence exerted by the thickness of the p+ diffusion layer on the basic characteristics of the solar cell has been studied. The optimal doping profile and the p-n-junction depth providing a high photovoltaic conversion efficiency at photocurrent densities of up to 100 A cm−2 have been determined.

The insertion of quantum dots in a host material produces band offsets which are greatly dependent on the field of strains brought about by this insertion. Based on the Empiric KP Hamiltonian model, the energy spectrum of the quantum dot/host system is easily calculated and a relationship between the conduction and valence band offsets is determined by the energy at which the lowest peak of the sub-bandgap quantum efficiency of an intermediate band solar cell is situated; therefore knowledge of the valence band offset leads to knowledge of both offsets. The calculated sub-bandgap quantum efficiency due to the quantum dot is rather insensitive to the value of the valence band offset. However, the calculated quantum efficiency of the wetting layer, modeled as a quantum well, is sensitive to the valence band offset and a fitting with the measured value is possible resulting in a determination of both offsets in the finished solar cell with its final field of strains. The method is applied to an intermediate-band solar cell prototype made with InAs quantum dots in GaAs.

The aim of the study is to apply a method commonly used to determine the efficiency of multi� junction nanoheterostructure III-V solar cells by analysis of the dark current-voltage (I-V) characteristics to such an unconventional semiconducting material as amorphous silicon. aSi:H and aSi:H/ μcSi:H p-i-n structures without a lightscattering sublayer or an an tireflection coating are studied. The results of measure� ments of the dark I-V characteristics demonstrate that the voltage dependence of the current has several exponential portions. The conversion efficiency of solar cells (SCs) is calculated for each portion of the dark I-V characteristic. This yields a dependence of the potential SC efficiency on the generation current density or on the photon flux. The observed agreement between the data derived from the experimental characteris� tics and results of calculations can be considered satisfactory and acceptable, thus the method suggested for measurement and analysis of dark I-V characteristics and tested earlier on SCs based on crystalline III-V compounds acquires a universal nature. The analysis of the characteristics of p-i-n amorphous silicon structures and the calculation of potential efficiencies, based on this analysis, extend the authors' understanding of this class of devices and make it possible to improve the technology and photoconversion efficiency of SCs of this kind.

A concentrator photovoltaic module with spectral splitting of solar radiation is developed. The module is based on a Fresnel lens and two dichroic filters. Solar cells based on AlGaAs and GaAs are grown by low-temperature liquid-phase epitaxy. GaSb photoconverters are fabricated by zinc gas-phase diffusion into a base epitaxial layer or an n-type GaSb substrate. The total efficiency of three solar cells developed for the spectral splitting module reached 39.6% (AM 1.5D spectrum).

Photovoltaic converters based on nGaInP/ n-pGe heterostructures grown by the OMVPE under different conditions of formation of the p-n junction are studied. The heterostructures are intended for use as narrowgap subcells of the GaInP/GaInAs/Ge threejunction solar cells. It is shown that, in Ge p-n junc� tions, along with the diffusion mechanism, the tunneling mechanism of the current flow exists; therefore, the twodiode electrical equivalent circuit of the Ge p-n junction is used. The diode parameters are determined for both mechanisms from the analysis of both dark and "light" current-voltage dependences. It is shown that the elimination of the component of the tunneling current allows one to increase the efficiency of the Ge subcell by ~1% with conversion of nonconcentrated solar radiation. The influence of the tunneling current on the efficiency of the Gebased devices can be in pr actice reduced to zero at photogenerated current density of ~1.5 A/cm 2 due to the use of the concentrated solar radiation.

A prototype compact TPV generator with a propane burner (pressure 2 bar) and a metallic netted emitter has been developed and tested. A photovoltaic generator unit with 24 (1 × 1 cm2) GaSb cells has been fabricated. The fabrication technology of photovoltaic cells has been optimized. It is shown that the data obtained can be used to select the starting bulk material for fabrication of photovoltaic cells with similar output parameters. It has been experimentally demonstrated that, to achieve maximum efficiency, it is necessary, in addition to using photovoltaic cells with similar characteristics, to provide identical conditions of their operation (temperature, illuminance).

A technique for determining a minority carrier’s diffusion length in photoactive III–V layers of solar cells by approximating their spectral characteristics is presented. Single-junction GaAs, Ge and multi-junction GaAs/Ge, GaInP/GaAs, and GaInP/GaInAs/Ge solar cells fabricated by hydride metal-organic vapor-phase epitaxy (H-MOVPE) have been studied. The dependences of the minority carrier diffusion length on the doping level of p-Ge and n-GaAs are determined. It is shown that the parameters of solid-state diffusion of phosphorus atoms to the p-Ge substrate from the n-GaInP nucleation layer are independent of the thickness of the latter within 35–300 nm. It is found that the diffusion length of subcells of multijunction structures in Ga(In)As layers is smaller in comparison with that of single-junction structures.

Two main issues governing the design of a solar concentrator module with triple-junction nano-heterostructure photovoltaic converters (PVCs) are considered: the effective concentration of radiation using Fresnel lenses and effective heat removal from PVCs. By theoretically and experimentally simulating these processes, the design parameters of module’ s elements are determined. A test batch of full-size modules has been fabricated. Each module consists of a front panel of small-size Fresnel lenses (a total of 144 lenses arranged as a 12 × 12 array) and the corresponding number of multilayer InGaP/GaAs/Ge PVCs. The PVCs are mounted on heat-distributing plates and are also integrated into a panel. The efficiency of the concentrator module with a 0.5 × 0.5-m entrance aperture measured under outdoor conditions is 24.3%, which is more than twice as high as the efficiency of standard (concentrator-free) silicon modules. In smaller test modules, the efficiency corrected for the PVC standard temperature (25° C) reaches 26.5%.

The effect of isovalent doping with P on the surface and bulk properties of the In0.53Ga0.47As alloy (below, InGaAs) was evaluated from variations in the photoluminescence and transmission spectra. It is established that isovalent doping decreases the nonradiative recombination rate in the bulk and on the surface of doped layers. The use of additional isovalent doping provided an improvement of parameters of the narrow� gap InGaAsbased solar cell used for the conversion of the concentrated solar radiation. The maximum effi� ciency of photovoltaic conversion in a spectral range of 900-1840 nm was 7.4-7.35% at a ratio of concentra� tion of the solar radiation of 500-1000 for the AM1.5D Low AOD spectrum.

Designs of thermophotovoltaic (TPV) generators with infrared emitters heated by concentrated solar radiation are developed, fabricated, and tested. Emitters made of SiC, W, or Ta of various forms and sizes are studied. To the GaSb-based thermophotovoltaic cells, the efficiency of transformation of thermal radiation of W emitters was 19%. The features of operation of two variants of TPV generators, namely, of cylindrical and conical types, are considered. In a demonstration model of the TPV generator consisting of 12 photocells, the output electric power with conversion of the concentrated solar radiation was P = 3.8 W.

The isovalent dopant diffusion from a localized source method was applied for the surface and bulk passivation of In 0.53 Ga 0.47 As (InGaAs) and GaAs layers. The passivation effects are characterized by low-temperature (77 K) photoluminescence (PL) spectroscopy. It has been found that phosphorus and/or indium doping from the gas phase increases effectively the PL intensity of InGaAs and GaAs layers. The phosphorus and indium diffusion into thin (∼100 nm) GaAs layers grown on the Ge substrate was carried out. The PL spectrum of these layers consists normally of a broadband emission line at ∼1.2 eV associated with the donor–acceptor pair recombination. Both donors and acceptors in GaAs are usually assigned to diffuse from the substrate Ge atoms occupying both Ga and As sites. Drastic changes of the PL emission after the phosphorous diffusion were observed: the intensity of the photoluminescence increases gradually, and the blueshift observed with the pumping energy increase is more pronounced. These changes are explained by a decrease in the nonradiative charge carrier recombination rate (e.g. at the GaAs–Ge heterointerface) by incorporation of phosphorus and indium atoms into GaAs during diffusion. This passivation method opens a promising way to improve the characteristics of multi-junction solar cells on Ge substrates.

The effect of the properties of interfaces with Group-III phosphides on characteristics of GaInP solar cells has been studied. It is shown that the large valence band offset at the p-GaAs/p-AlInP interface imposes fundamental limitations on the use of p-AlInP layers as a wide-band-gap window in p-n structures of solar cells operating at ratios of high solar light concentration. It is demonstrated that characteristics of p-n solar cells can be, in principle, improved by using a double-layer wide-band-gap window constituted by p-Al0.8Ga0.2As and p-(Al0.6Ga0.4)0.51In0.49P layers.