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A photovoltaic effect was observed under exposure to 810-nm laser light on the atomically clean surface of an n-GaAs wafer etched with Ar+ ions: open-circuit voltage in current–voltage (J–V) light characteristics was as high as 47 mV. The effect is due to the formation of a p–n structure under Ar+ ion bombardment in the near-surface bulk layer (~ 7 nm thick) via the conversion of the conductivity type of the near-surface layer from n to p. The effect of the conductivity type conversion under pure mechanical ion action manifested itself in that the Fermi level approached the valence band top, which was detected by high-resolution photoelectron spectroscopy with the use of a synchrotron radiation. The formation of the p–n junction in the structure was confirmed by dark J–V characteristics, which show a diode effect at voltages in the range (0–0.6) eV with a direct-to-reverse current ratio as large as 103. The results obtained show that the near-surface bulk properties of n-GaAs treated by the most widely employed surface cleaning procedure via etching with a beam of Ar+ ions differ dramatically from the pristine deep bulk.

The creation of connecting tunnel diodes with a peak tunneling-current density higher than the density of the short-circuit current of photoactive p–n junctions is an important task in the development of multijunction photoconverters (III–V) of high-power optical radiation. Basing on numerical simulation of the J–U characteristics of tunnel diodes, a method is proposed for increasing the peak tunneling-current density by including a thin undoped i-type layer with a thickness of several nanometers between degenerate layers of the tunnel diode. The p–i–n-GaAs/Al0.2Ga0.8As structures of the connecting tunnel diodes with a peak tunneling-current density of up to 200 A/cm2 are grown by molecular-beam epitaxy.

A highly defective ~10-nm-thick layer was fabricated in a high vacuum by 2.5 keV Ar+ ion bombardment of the n-GaAs surface. Valence band photoelectron spectra showed a p-type conductivity of the layer arising due to the high concentration of mechanically created point defects (p-centers). J–V characteristics measured ex situ for the structure consisting of the irradiated p-layer on the n-type substrate revealed a diode effect. Analysis of the data attributes the effect to the formation of a specific p–n junction. Thereby, we demonstrated that Ar+ ion bombardment of the n-GaAs surface results in that a nanostructure with the p–n junction properties is formed. The p–n junction under consideration seems to deserve further study and possible application since it can be formed in high-vacuum clean conditions directly by exposure to a low-energy Ar+ ion beam without wet lithography.

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.

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.

The possibility of creating of a radioisotope source of energy based on a radio-luminescent crystal of YPO 4:Eu/(238 Pu) and AlxGa1-xAs/GaAs photovoltaic converter is demonstrated and its characteristics are analyzed. A prototype of an ecologically safe radioisotope source with low content (< 0.1%) of the 238Pu isotope, efficiency of ~1.4%, and long service life has been developed.

Investigations of the temperature stability of the peak tunneling current density of connecting tunneling diodes, which are necessary for the creation on their basis of multijunction photoconverters of powerful optical radiation, have been carried out. The structures of n++-GaAs/i-GaAs/i-AlGaAs/p++-AlGaAs of connecting TD with an intermediate undoped layer thickness of 7.5 nm and a growth temperature of 500 °C (structure ”A”) and with a thickness of 10 nm and a temperature of 450 °C (structure ”B”) were investigated. When heated to 80 °C, an increase in the peak tunneling current density of the TD structure ”B” by 4% is observed. However, for structure ”A”, a decrease in the peak tunneling current density by 5% with heating is observed. The factors leading to the appearance of a negative or positive temperature coefficient of the peak tunneling current density are determined using mathematical modeling of tunneling diodes based on GaAs/AlGaAs materials. By reducing the epitaxial growth temperature of n++–GaAs/i-GaAs/i-AlGaAs/p++–AlGaAs tunnel diode structure to 450 °C and including an undoped i-layer 10 nm thick between the degenerate layers ensure the temperature stability of peak current density when heated to 80 °C.

High-efficiency multijunction photoelectric converters of high-power optical emission, based on III-V materials, are presently the most promising for application in concentrator photovoltaics and radio-photonics. With increasing power of the optical emission to be converted, the influence exerted by connecting tunnel diodes on the efficiency of multijunction photoelectric converters becomes more pronounced. To provide the maximum efficiency of multijunction photoelectric converters, the connecting tunnel diodes must have a high density of the peak tunneling current, low differential resistance, and maximum optical transparency to minimize the optical loss. Efforts were made in the study to develop high-efficiency connecting p++–i–n++ tunnel diodes on the basis of GaAs/AlGaAs structures grown by molecular-beam epitaxy, with peak tunneling current of up to 200 A/cm2. These types of tunnel diodes are to be used as connecting elements in multijunction concentrator solar cells and high-power multijunction photoelectric converters based on III-V materials.

Some results of studies on the creation of new junction elements for application in monolithic multijunction InP based photovoltaic cells are presented. A new type of junction elements with a specific ohmic resistance of less than 2 mΩ cm2 within a range of current densities of up to 700 A/cm2 is presented as an alternative to tunnel junctions.

We have studied the degradation of photoelectric characteristics of heterojunction solar cell samples based on α-Si:H/Si structures upon irradiation by electrons with an energy of 3.8 MeV and fluences of 1 × 1012–1 × 1014 cm–2. It is shown that the efficiency of the samples of heterojunction solar cell elements under the conditions of AM0 illumination (0.136 W/cm2) is reduced by 25% at a fluence of 2 × 1013 cm–2. This is more than an order of magnitude higher than the critical fluence value achieved previously when silicon solar cells with a p–n junction and an n-type base were irradiated by high-energy electrons.

Characteristics of double-cascade nonmonolithic p-i-n AlGaAs/GaAs photovoltaic converters of high-power laser radiation, electrically combined with n++-GaAs/i-GaAs/i-AlGaAs/p++-AlGaAs tunnel diodes, have been studied. The AlGaAs/GaAs p-i-n structures of the photovoltaic converters and n++-GaAs/i-GaAs/i-AlGaAs/p++-AlGaAs tunnel diodes were grown by molecular-beam epitaxy. The photoelectric characteristics of the double-cascade AlGaAs/GaAs photovoltaic converters were examined in the temperature range from 103 to 298 K under excitation with a laser light wavelength of 809 nm and a power density ⩽92 W/cm2. The double-cascade p-i-n AlGaAs/GaAs nonmonolithic photovoltaic converters of planar design had a fill factor of 0.88 and efficiency of 58.2% at a temperature of 103 K. It was shown experimentally that the current-voltage characteristics of the connecting n++-GaAs/i-GaAs/i-AlGaAs/p++-AlGaAs tunnel diodes affect the photoelectric parameters of the double-cascade photovoltaic converters of high-power laser light.

We present original design and performance simulations of four-junction heterovalent concentrator solar cells with monolithically integrated junctions based on Ge, III–V, and II–VI semiconductors. The developed design relies on the formation of a metamorphic buffer layer matching lattice constants of a Ge junction and three more junctions based on InGaAs, AlInGaAs, and a ZnSe/CdSe short-period superlattice. Utilizing of an n+-type chlorine-doped layer of ZnCdMgSe as a highly transparent conductive window is proposed. Experimental results are reported, demonstrating the potential of molecular beam epitaxy to fabricate such solar cell heterostructures atop of a Ge p–n junction formed in a Ge substrate.

Current-voltage and capacitance-voltage characteristics of tunnel diode structures with GaAs-n++/i-GaAs/i-Al0,2Ga0,8As/Al0,2Ga0,8As-p++ active region and i-layer thicknesses of 7.5 nm and 10 nm and epitaxial growth temperature of 450 °C and 500 °C have been studied. The tunnel diode structures grown by the molecular beam epitaxy technique are intended for application as connecting elements in multijunction photovoltaic converters of high-power monochromatic optical radiation. According to the results obtained, the peak tunnel current density of up to 200 A/cm2 is achieved. Forward current-voltage and capacitance-voltage characteristics of tunnel p-i-n diode structures were measured at room temperature. The capacitance-voltage characteristics of the tunnel diodes being tested were obtained experimentally with the frequency dependence of S-parameters simulated within 10-1000 MHz at bias voltages of 0.4–1 V.

We present the results of optimization of the design and molecular beam epitaxy (MBE) growth technology of N-AlGaAs:Si/n +-GaAs:Si/p +-GaAs:Be/P-AlGaAs:Be heterostructures for tunnel diodes (TDs). The achieved maximum peak current density level (J p = 513 A/cm2) allows these TDs to be used for cascade connections both in multijunction solar cells and in structures of tunnel-coupled laser diodes. The initial region of the J–U curve of TDs exhibits nonlinearity that is explained by a residual potential barrier left in the p +–P–p + isotype heterojunction (confining the active region of TD) as a result of non-optimum doping of Al0.4Ga0.6As alloy.

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.

Simulation of the structure of multijunction photodiodes has been performed on the assumption that an equal of the number of photons is absorbed in them, and PV characteristics have been stadied AlxGa1-xAs/GaAs photodiodes fabricated by the molecular-beam epitaxy technique. According to the performed measurements and analysis of the results, it has been shown that the efficiency of single-junction photodiodes in converting monochromatic optical radiation at a wavelength of 810 nm reaches 50%. The relationship between the "saturation" currents calculated from the dark I - V characteristic for the diffusion current flow (Shockley) in the space charge region of a photodiode p-n junction and the obtained values for the efficiency of converting optical radiation in the wavelength range of 700 - 900 nm has been shown. When the "saturation" current flow for the diffusion mechanism rises by an order of magnitude, the efficiency value at excitation by monochromatic radiation at 810 nm and 780 nm drops by 25% and 11%, respectively.

In this paper, we report on the initial studies of connecting elements for cascade photodetectors. The heterostructures used in this work are based on InP. As a connecting element, it is proposed to use nanocrystalline inclusions instead of the tunnel junction. GaP nanocrystals are most suitable for this purpose because this material does not cause absorption of the incident radiation.

In this work we present a post-growth fabrication process, in which the separation of InGaP/Ga(In)As/Ge epitaxial wafers into individual elements is done in a single-stage wet chemical etching process, which produces a smooth etching profile. This process makes it easier to apply a passivating protective layer to the element mesa sidewall, increasing both average cell efficiency and reliability. To assess fabricated multi-junction solar cell quality, dark J-V characteristics were measured directly on the epitaxial wafer at current densities of (1⋅10−12 ‐ 10) A/cm2 and voltages of (0 - 3) V. The dominating current flow mechanisms and their corresponding pre-exponential factors J0i were determined, and estimates of cell efficiencies made. We have demonstrated that the post-growth processes with single-stage separation etching of InGaP/Ga(In)As/Ge epitaxial wafers allows fabricating multi-junction solar cells with very similar J-V characteristics, similar low values of pre-exponential factors corresponding to "tunnel-trap" (overabundant) and "recombination" current flow mechanisms and high efficiencies.In this work we present a post-growth fabrication process, in which the separation of InGaP/Ga(In)As/Ge epitaxial wafers into individual elements is done in a single-stage wet chemical etching process, which produces a smooth etching profile. This process makes it easier to apply a passivating protective layer to the element mesa sidewall, increasing both average cell efficiency and reliability. To assess fabricated multi-junction solar cell quality, dark J-V characteristics were measured directly on the epitaxial wafer at current densities of (1⋅10−12 ‐ 10) A/cm2 and voltages of (0 - 3) V. The dominating current flow mechanisms and their corresponding pre-exponential factors J0i were determined, and estimates of cell efficiencies made. We have demonstrated that the post-growth processes with single-stage separation etching of InGaP/Ga(In)As/Ge epitaxial wafers allows fabricating multi-junction solar cells with very similar J-V characteristics, similar low values of pre-exponential factors corresponding t...

The forward dark current density – voltage (J-V) characteristic is one of the most important characteristics of multi-junction solar cells. It indicates that the mechanisms of current flow in the space charge region of photoactive p-n junctions. If one is to idealize the optical and electrical (coupling) elements of the solar cells, it is the J-V characteristic that determines the theoretically possible efficiency of the solar cell. In this paper, using the connection between the dark J-V and photovoltaic (η-Jg) efficiency – generated current density characteristics, the effect of current transport mechanisms in the space charge on the efficiency of multi-junction solar cells was investigated in the temperature range of 300 – 80 K. In the experimental J-V and η-Jg curves of the multi-junction solar cells, segments corresponding to the dominant current transport mechanisms were identified. The developed method, based on the analysis of forward dark J-V characteristics, makes it possible to identify the par...

Characteristics of GaAs photodiodes have been studied before and after the chemical nitridation of their surface in hydrazine sulfide solutions, which leads to substitution of surface As atoms with N atoms to give a GaN monolayer. The resulting nitride coatings hinder the oxidation of GaAs in air and provide a decrease in the density of surface states involved in recombination processes. The device characteristics improved by nitridation are preserved during a long time.

Forward dark and load I - V characteristics of triple-junction GaInP/Ga(In)As/Ge solar cells (SCs) in the temperature range 300 - 80 K have been studied. At temperatures below 200 K, jumps of current and voltage in, respectively, dark and load characteristics were observed experimentally and attributed to the existence of a counter potential barrier formed by isotype heterolayers between the tunnel diode and the Ge p-n junction in the InGaP/Ga(In)As/Ge SC. An analysis of the forward dark characteristics of GaInP/Ga(In)As/Ge SCs, recorded at 80 K, enabled evaluation of the potential and real conversion efficiencies of incident sunlight. The influence exerted by the shape of the side mesa surface of GaInP/Ga(In)As/Ge SCs on the dominant current flow mechanisms was analysed. A method for single-step separate etching was suggested and studied. This method allows one to reduce surface leakage currents and raise the yield of suitable SCs with an efficiency greater than 35% at low sunlight concentrations (C = 10 - 100, T = 300 K). The suggested post-growth technology reduces the number of fabrication operations and the SC production cost and improves the reliability of the SC operation in a wide temperature range.