Maxim Shvarts

• PhD
• Senior Researcher at Russian Academy of Sciences

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...

The Ge-based photovoltaic laser-power converters (LPCs) for wireless IR energy delivery approach with a wavelength of λ = 1550 nm are studied and developed. It is shown that the doping by diffusion from the gas phase with zinc gives rise to a notable increase in photosensitivity compared with the doping with diborane, phosphine, or antimony (includ...

The paper presents a promising solution for photovoltaic modules that provides overcoming the main conceptual limitation for the concentrator concept in photovoltaics --- the impossibility to convert diffused (scattered) solar radiation coming to the panel of sunlight concentrators. The design of a hybrid concentrator-planar photovoltaic module bas...

Optimized photoconverters for operation under high-power laser radiation in the green-red spectral range based on MOCVD-grown GaInP/GaAs heterostructures are fabricated. The Au(Ge)/Ni/Au and Pd/Ge/Au contact systems have been studied to form the front contact grid of devices. As a result, the laser photoconverter with a Pd/Ge/Au contact showed an e...

A new experimental method for obtaining resistive-less dark current-voltage (IV) characteristic of multi-junction solar cells has been developed. The method realizes by measuring dark voltage, dark current, and additional measurements of the electroluminescence (EL) intensity of subcells. It has been shown that in the resistive-less mode (low curre...

The issues concerning the stability of contact systems in GaSb photovoltaic converters and their reliability enhancement have been considered. It is established that at thermally induced degradation conditions (i.e., at the constant heat load at 80, 120, and 200 °C), the contacts with a conducting Ag layer, namely, Ti-Pt-Ag, Ti-Pt-Ag-Au, Cr-Au-Ag-A...

GaInP-based laser power converters (LPC) structure grown byMOVPE and device chip design have been optimized for operation underhigh-power lasers of the green-red spectral range. Light I-V curves recordshave shown the performance of the LPC at up to 40-50 W/cm ² ofincident power densities. The highest level data were obtained for 532,600, and 633 nm...

In photovoltaic converters of concentrated sunlight, the thermal flow isdirected from the photoactive region (p-n junction) to a heat-spreadingbasement through the substrate. The heat sink transfers the excess thermalto the environment by convection or cooled by a liquid carrier. Reducingthe thickness of the substrate makes it possible to reduce th...

The efficiency of GaInP/GaAs/In x Ga 1-x As triple-junction solar cells obtained by replacing (in the widely used "classical" GaInP / GaAs / Ge heterostructure) the lower germanium with In x Ga 1-x As subcell formed using the metamorphic growth technology has been investigated. Based on an original approach, the optimal indium concentration in the...

Developed and investigated are IR (850 nm) light-emitting diodes based on AlGaAs/Ga(In)As heterostructures grown by the MOCVD technique with multiple quantum wells in the active region and with a double optical reflector consisted of a multilayer Al 0.9 Ga 0.1 As/Al 0.1 Ga 0.9 As Bragg heterostructure and an Ag mirror layer. Light-emitting diodes w...

The effect of positioning of the In 0.8 Ga 0.2 As 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 r...

In the work, the effect of In 0.8 Ga 0.2 As quantum dots position in the i-region of a GaAs solar cell on its spectral and photoelectric characteristics has been investigated. Three solar cell structures were obtained by metal-organic vapor-phase epitaxy, in which layers of quantum dots were placed in the middle of the i-region and also have been s...

This paper discusses multijunction solar cells with optically coupled p-n junctions under radiation exposure photosensitivity spectral response study. It is shown that if the measurement technique does not consider the luminescent coupling and does not track the optical coupling degradation, then instead of a decrease (which is a natural response o...

Temperature dependencies of the refractive indices, $n$ , for ${{\rm In}_x}{{\rm Ga}_{1 - x}}{\rm As}$ and ${{\rm In}_x}{{\rm Al}_{1 - x}}{\rm As}$ metamorphic layers with $x = {0.06} {-} {0.25}$ have been determined. For this purpose, we performed variable-temperature (80 to 400 K) measurements of the specular reflection coefficient using custom d...

The results of studying the In x Ga 1−x As 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.

Quantum objects in the host material of photovoltaic converters can expand the spectral sensitivity to the long-wavelength spectral region. Samples with InAs quantum dots and thin layers in the host GaAs material were studied theoretically with the assumption of high-power laser subband irradiation input. Threshold factors have been established tha...

The temperature dependences of the diffusion and recombination saturation currents and the energy gap have been obtained for a GaAs photoelectric converters. Saturation currents by IV characteristic analysis, and the energy gap by electroluminescence peak position have been determined. It has been shown that the relationship between saturation curr...

The experimental characteristics of GaAs p-i-n structures with InGaAs quantum objects (QOs) have been investigated. The study of electroluminescence spectra has shown that an increase of the number of QOs layers leads to relative increase in electroluminescence intensity from QOs and decrease it from the GaAs matrix. The observed increase in QOs re...

In the work the effect of the number of In 0.8 Ga 0.2 As 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 electrolum...

The IV characteristics of previously found structure fragment with not optimized isotype hetero-barriers in the bottom connecting part of triple-junction GaInP/GaAs/Ge solar cell has been investigated. It has been shown that there are various ways to obtain the IV-curves of such fragment, including by creating structures containing only an isotype...

In-depth study of the method for modifying the spatial and spectral irradiation distribution from a Fresnel lens concentrating sunlight on a multi-junction solar cell is proposed. An approach considered to constructing a Fresnel profile is based on the principle of independent control of the slope angles of the refracting faces of individual teeth...

The photocurrent generation profiles in a multi-junction solar cell under concentrated sunlight originated from the Fresnel Lens are investigated both theoretically and experimentally. The design parameters for the FL-SC couple were determined, at which the local current-limiting effect from the Ge subcell had been either appeared or disappeared. D...

GaAs solar cells with different number of rows of GaInAs quantum objects have been studied. It has been shown that recombination through quantum objects linearly increases with respect to recombination through the bulk GaAs with the number of rows increases. The ratio of the saturation currents of p-n junctions with and without quantum objects, whi...

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 minim...

In this work GaAs photovoltaic converters for high-power laser radiation were investigated in high optical pumping conditions. Radiative heating of the sample under test can be avoided by reducing the duty cycle of the illumination pulses. This work discusses the application boundaries of such a research method. The barrier and diffusion capacitanc...

The concentrator photovoltaic modules efficiency and their power generation are strongly dependent on the accuracy of their orientation by a tracking system towards the Sun. The more the solar cell power concentration ratio, the more stringent requirements are imposed on the module’s guidance system and tracking accuracy in the direction of the Sun...

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 L...

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...

The effect of irradiation by protons with an energy of 15 MeV with fluences of (1-40)٠10¹² cm⁻² on the spectral characteristics of UV 4H-SiC photodetectors was considered. Photodiodes with Schottky barriers were formed by thermal vacuum sputtering with a thickness of 20 nm and a diameter of 8 mm on 4H-SiC structures with CVD epitaxial layers with a...

An option for the structural design of the metamorphic InGaAs photovoltaic converter is presented. The peculiarity of the proposed device is the ability to operate efficiently with the high-power 1064 nm laser radiation at the elevated up to +125°C temperatures. The temperature dependencies of the output photovoltaic parameters for two types of In...

The fundamental reason for the decrease in solar cell (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 the nanostructure medium in p–i–n GaAs SCs, it is possible to partially suppress recombi...

A study of GaAs solar cells (SCs) with various quantum-sized objects has been carried out. In0.2Ga0.8As quantum wells, In0.4Ga0.6As quantum well-dots (QWDs), In0.8Ga0.2As and InAs quantum dots have been considered. The increment in photocurrent and the reduction of open-circuit voltage have been calculated using dark IV and spectral characteristics...

Studies of electronic transitions in the photoconverters with In0.4Ga0.6As quantum well-dots (QWD) layers have been carried out. It is shown that the quantum yield and electroluminescence spectral peaks are well described by e1-lh1 and e1-hh1 optical transitions in the quantum well with the same average composition and thickness. The energy of the...

Semiconductor heterostructures allow solving the problems of controlling the fundamental parameters of semiconductor devices owing to the possibility of change in the electronic band structure, bandgaps and refractive indices of a material itself during epitaxial growth, as well as effective masses and mobilities of charge carriers in it.

The possibility of using lateral Ga(In)AsP nanostructures grown by the catalytic method in a quasi-closed volume from phosphorus and indium vapors on the GaAs (100) surface as an antireflection coating for photovoltaic devices is considered for the first time. It is shown that, at a fixed growth temperature, it is possible to control the surface mo...

The paper is devoted to the relationship between the energy gap and the saturation currents (diffusion and recombination ones) of GaInAs homo p–n junctions. Such a relationship is required for developing multi-junction solar cells and photodetectors for a given wavelength. The saturation currents and the energy gap have been determined experimental...

In this work, physical and optical properties of In 0.8 Ga 0.2 As quantum dots (QDs) embedded in the structure of a single-junction GaAs solar cell (SC) grown by MOVPE technique were investigated using spectral characteristics of external quantum yield (EQE) and electroluminescence (EL). It has been found that, in characterizing QD physical paramet...

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 lase...

In the present work processes of direct light coupling in the triple-junction solar cells between top GaInP (wide band gap) and bottom Ge (narrow band gap) subcells are considered, when parameters of intermediate optical medium (comprised of middle GaAs p-n junction layers) are changed. Conditions of luminescent coupling gain and blocking are studi...

p–i–n GaAs photovoltaic converters of modulated laser radiation (810–830 nm) transferring both energy (laser power) and information signal were developed. The capacitance and frequency characteristics of the photovoltaic converters at a constant 0.2–1 W and variable 16 mW laser power were studied. The dependences of the heterostructures capacitance...

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 t...

Quantum photoresponse yield of a silicon XUV avalanche photodiode prototype with 1.5‑mm-diameter active region has been studied in the 320–1100 nm wavelength range. It is established that the proposed avalanche photodiode has the external quantum efficiency above 20 electron/photon in the 580–1000 nm range at a reverse bias voltage of 485 V.

The “top” intergenerator part situated between the GaInP and GaAs subcells (electric power generators) is analyzed. The shape of the light current–voltage characteristics and the Voc–Jsc (open-circuit voltage–short-circuit current) dependence are examined. It is found that the p⁺–n⁺ tunnel heterojunction situated in the “top” intergenerator part ca...

Solar spectral irradiance blurring in the focal plane of the Fresnel lens arising from the chromatic aberration (CA) inherent to a lens was studied. The experimental complex for recording both irradiance distribution and spectral irradiance redistribution for the radiation concentrated by a small-sized energy concentrator based on a solar simulator...

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...

“Solar” Abbe number is proposed to operate in assessing the suitability of optical materials at sunlight concentrators manufacture. Comparative results are presented for materials practically used in concentrator photovoltaics from the point of view of designing Fresnel lenses from them with a high average concentration in the focal spot of the min...

In this paper, triple-junction solar cells of various middle junction thickness are studied. It is shown that in samples with thin layers, an optical coupling between the top and the bottom subcell is possible as well as a direct leakage of external radiation through the middle one. True values of the spectral dependences of the external quantum ef...

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...

The temperature characteristics of GaAs solar cells with 0, 1, 5, 10 and 15 rows of GaInAs quantum objects have been investigated. Introducing of quantum objects into GaAs p-n junction leads to open circuit voltage drop due to the changing recombination transition energy from GaAs energy gap value to the effective one (Egeff = EgGaAs − ΔEg). It has...

In the present work processes of light redistribution within the multijunction solar cell were investigated. The possibility to control efficiency of luminescent coupling, up to its totally blocking, is described. Temperature of the tested sample is used to provide optical coupling management. Direct penetration of recombination photons from top to...

We present Ag-free low-concentrator bifacial indium-fluorine-oxide (IFO)/(n⁺pp⁺)Cz-Si/indium-tin-oxide (ITO) solar cells based on: (i) a shallow phosphorus-doped n⁺-emitter; (ii) an easy-to-fabricate screen-printed Al-alloyed Al-p⁺ back-surface-field (BSF); (iii) transparent conductive IFO and ITO layers grown by ultrasonic spray pyrolysis, which a...

At high laser radiation a PV converter output parameters are greatly influenced by its heating. Open circuit voltage could be an indicator of temperature drift. The dynamics of the heating process of GaAs PV cell was investigated for cases of sufficient and insufficient heat removal. The conditions of insufficient heat removal are discussed.

This study is aimed at the development of laser-radiation converters (LPC) for the wavelength of 1550 nm, which can operate efficiently upon the increase of irradiation power. The photovoltaic structures are produced by Zn diffusion from the gas phase into n-GaSb bulk wafers or base layers grown by liquid phase epitaxy. The output parameters of dev...

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 over...

A quantitative error analysis in determining minority charge carrier lifetimes in photoactive layers of III-V photovoltaic cells (multijunction solar and laser power converters) has been carried out. Accuracies of the methods based on simulation: of the spectral dependencies of the internal quantum yield, of photovoltaic cells’ dark current densiti...

In the paper, the approaches to the Fresnel lens design in a rectilinear (“classical”) and a curvilinear (“aspherical”) refracting profile versions are discussed regarding silicone-on-glass and 3D printing technology. The advantages of short-focus lenses with an increased Fresnel profile pitch are shown. The mathematical model used for concentratin...

The results of a study and the development of a module designed for energy transmission via atmospheric channels are presented. The four-cell module based on single-junction metamorphic InGaAs/GaAs converters grown by metal-organic vapor-phase epitaxy has an open-circuit voltage of ~3 V. It is shown that the monochromatic efficiency (at a wavelengt...

The sensitivity at wavelengths in the range 400–1150 nm, dark current, and dynamic characteristics of an silicon avalanche photodiode with an active region 1.5 mm in diameter that we developed have been examined. It has been shown that the avalanche photodiode has the following set of characteristics: sensitivity 80–85 A/W at wavelengths of 900–101...

The work is aimed at the study of multijunction solar cells with built-in Bragg reflectors. The possibility to use the photon structure for "locking" the secondary recombination radiation, which causes luminescent coupling between individual photoactive p-n junctions in a solar cell, is investigated. Temperature studies were carried out on the refl...

Temperature photovoltaic dependencies have been measured at 90-350 K for a single-junction GaAs-based p-i-n solar cell and for a similar solar cell with imbedded in i-region In 0.4 Ga 0.6 As quantum objects. A theoretical approach for analyzing temperature dependencies of open circuit voltage has been proposed. A dethermalization of quantum objects...

Series resistance in solar cells limit their maximum conversion efficiency and thus should be minimized. Generally, such losses originate from deficiencies at the contact or absorber level. Quantifying them is the first step for tackling its reduction. In this work, we provide a new way to assess the series resistance in nanowire-based solar cells,...

AlGaAs/GaAs-based semiconductor photovoltaic converters (PVCs) of laser radiation, capable of operating at an illuminance up to 9 kW/cm² with retained isothermal state have been studied. This state was confirmed by the logarithmic shape of dependences of the open-circuit voltage on the power density of incident laser radiation. At maximum illuminan...

Characteristics of heterostructure PV converters under ultra-high high power frequency modulated laser beams have been modeled and investigated. Dynamic properties of GaAs based multijunction cells have been studied, and estimations of efficiencies for such devices were carried out. It has been established that high efficiency values for conversion...

The overheating effect of high-power GaAs laser photoconverters has been studied. The dependence of the p-n junction overheating temperature ΔΤ on the photogenerated current I g , which is proportional to the laser radiation power, has been obtained. It is shown that the open circuit voltage (Voc) drop is caused by the p-n junction overheating effe...

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 a...

In the present research, a multijunction solar cell with a built-in 1D photonic structure − Bragg reflector − is investigated. The joint effect of photon recycling and luminescence coupling on the spectral characteristics of the external quantum efficiency of multijunction solar cells is considered.

Numerical simulation of a steady state thermal regime of photovoltaic modules with sunlight concentrators has been performed. Contribution of different heat transfer mechanisms in the total thermal balance was analysed. The applicability of the single cell model for calculating the photovoltaic module thermal regime was investigated using an assump...

In the work, GaAs solar cells (SCs) structures with embedded InAs and Ina8Gaa2As arrays of quantum dots (QDs) was obtained by metalorganic vapor-phase epitaxy. The spectral characteristic of internal quantum yield of grown SCs were measured and it was shown that the use of InGaAs QDs allows preserving the quality of the p-n junction even at embeddi...

In the present work, an opportunity to block the negative influence of luminescent coupling between subcells in multijunction solar cells with help of built-in Bragg reflectors is investigated. Temperature modes, at which the blocking of optical interaction in the GaAs-Ge pair of subcells is possible, have been determined.

By modeling solar cells with quantum dots based on A3B5 materials it is necessary to take into account the large number of localized quantum levels arising in the forbidden band of the host material. In this paper Empiric k-p Hamiltonian model have been used to describe InAs/GaAs structure. For the model two shape of quantum dot: box and cylinder h...

The tunnel (intergenerator) part between the middle (GaAs) and bottom (Ge) subcell of a GaInP/GaAs/Ge triple-junction solar cell was investigated. It is shown that the previously observed features of the multi-junction solar cells IV-curves, namely the inflection of the characteristics, arises from heterointerfaces in the region between the GaAs p-...

In the work, GaAs photovoltaic convertor structures with embedded In0.8Ga0.2As arrays of quantum dots (QDs) have been obtained by metalorganic vapor-phase epitaxy. Spectral characteristic of internal quantum yield showed two spectral peaks at 930 and 985 nm of photosensitivity beyond the GaAs absorption edge. A theoretical calculation of the band t...

Presented are technical solutions on constructing optical systems for experimental simulating the sunlight parameters. Designs of two types of solar simulators are proposed. In the first one, the spectrum and the radiation angular divergence are simulated on the basis of a continuous light source, what corresponds to the principle "necessity and su...

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 pho...

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 a...

Photovoltaic structures on the basis of GaAs p–i–n junctions with a different number of In0.4Ga0.6As layers in the space-charge region forming quantum-confined objects are experimentally and theoretically investigated. For all structures, the dependences of the open-circuit voltage on the solar-irradiation concentration are analyzed. It is shown th...

A theory is developed, which describes the experimental external quantum efficiency, EQE(λ) as a function of photon wavelength for structured Si-based solar cells. Short-circuit current density as a function of base thickness, d, is calculated for the high-efficiency solar cells with the photoconversion efficiency η ≥ 25% The procedure allows one t...

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 ana...

This paper evaluates annual energy delivery from a Solar PhotoVoltaic Installation (SPVI) based on most advanced III-V CPV technology combined with a conventional thin-film flat-plate concept. The goal of the proposed integration was to capture both direct and diffuse sunlight in one module, increasing efficiency in PV conversion of global solar ra...

The paper completes the study of the photoconverter overheating during IV-curve recording on the pulse simulator of solar radiation. It is experimentally found that after switching on the pulse of light photoconverter voltage decreases linearly with time. The voltage decrease rate proportionally depends on photogenerated current. It has been theore...