Hybrid quantum well-dots (QWD) nanostructures have been formed by deposition of 7-10 monolayers of In0.4Ga0.6As on a vicinal GaAs surface using metal-organic chemical vapor deposition. Transmission ...electron microscopy, photoluminescence and photocurrent analysis have shown that such structures represent quantum wells comprising three-dimensional (quantum dot-like) regions of two kinds. At least 20 QWD layers can be deposited defect-free providing high gain/absorption in the 0.9-1.1 spectral interval. Use of QWD media in a GaAs solar cell resulted in a photocurrent increment of 3.7 mA cm−2 for the terrestrial spectrum and by 4.1 mA cm−2 for the space spectrum. Diode lasers based on QWD emitting around 1.1 m revealed high saturated gain and low transparency current density of about 15 cm−1 and 37 A cm−2 per layer, respectively.
Photovoltaic converters of high-power (λ = 800–860 nm, ELR = 150–550 W/cm2) laser radiation (PhotoVoltaic Laser Power Converters – PVLPCs) based on AlGaAs/GaAs heterostructures grown by metalorganic ...vapor-phase epitaxy have been developed. To increase the output voltage, the space charge region of p-GaAs/n-AlхGa1-хAs heterojunction was shifted to the n-AlхGa1-хAs wide-gap layer with a gradual “x”. The technology for embedding a rear reflector based on TiOx/SiO2/Ag into the photovoltaic converter structure by “transferring” the heterostructure to a supporting substrate and the method of bonding to form a monolithic structure of the PVLPC has been elaborated. To operate the heterostructures at an increased power density of laser radiation, they have been designed to eliminate possible potential barriers at the heterointerfaces and the frontal contact topology with a high density of the metal grid (50 μm and 125 μm contact pitch are under consideration) has been employed. PVLPCs with efficiency of 62% were obtained at the power density of monochromatic radiation (λ = 850 nm) ELR = 170 W/cm2. The finger pitch of 50 μm allows keeping efficiency more than 56% even with a fivefold increase in laser radiation (up to ELR = 500 W/cm2).
•AlGaAs/GaAs photovoltaic converters of high-power laser radiation were grown by MOVPE.•p-GaAs/n-AlGaAs heterojunction is used for decreasing injection current.•Carrier lifetime is increased with rear reflector for "inverted" heterostructure.•Optimal front contact pitch for both high laser power and for high SR is developed.•PVLPC efficiency doesn't fall below 56% for laser power up to 0.5 kW/cm2 (62% max.eff).
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 experimentally, and an empirical exponential formula was obtained for the required relationship. The results of the work allow predicting the saturation current for a GaInAs p-n junction with a given energy gap.
A number of important but little-investigated problems connected with III-V/Ge heterostructure in the GaInP/GaInAs/Ge multijunction solar cells grown by MOVPE are considered in the paper. The ...opportunity for successfully applying the combination of reflectance and reflectance anisotropy spectroscopy in situ methods for investigating III-V structure growth on a Ge substrate has been demonstrated. Photovoltaic properties of the III-V/Ge narrow-band subcell of the triple-junction solar cells have been investigated. It has been shown that there are excess currents in the Ge photovoltaic p-n junctions, and they have the tunneling or thermotunneling character. The values of the diode parameters for these current flow mechanisms have been determined. The potential barrier at the III-V/Ge interface was determined and the origin of this barrier formation during MOVPE heterogrowth was suggested.
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 InxGa1-xAs laser-power converters are presented in regard to In content: with x = 0.23 and x = 0.18 and with an efficiency of ∼50% and ∼40% (25 °C), respectively. For In0.18Ga0.82As device, an increase in efficiency of up to 50% is recorded upon transition to a temperature range of 50÷60 °C with maintaining efficiency at a level of more than 45% at elevated to 100 °C operating temperatures. In comparison, the "standard" In0.23Ga0.77As device performs a negative efficiency trend within a whole temperature range with absolute values below 45% in practically important operating modes of +75÷100 °C.
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
V
oc
–
J
sc
...(open-circuit voltage–short-circuit current) dependence are examined. It is found that the
p
+
–
n
+
tunnel heterojunction situated in the “top” intergenerator part can operate as a photoelectric source counteracting the base
p
–
n
junctions. In this case, the
V
oc
–
J
sc
characteristic has a descending part, and a sharp jump can be observed. This undesirable effect becomes weaker with increasing peak current of the tunnel junction.
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 relative to the electric field of the
p–n
junction. The displacement of the QD array to the boundary of the weakly doped base leads to a decrease in the photogenerated current. But at the same time, the voltage drop effect, which is well-known for nanoheterostructural SC, is minimal.
Photovoltaic structures on the basis of GaAs
p
–
i
–
n
junctions with a different number of In
0.4
Ga
0.6
As 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 that the implantation of quantum objects leads to the dominance of recombination in them over recombination in the matrix, which manifests itself in a drop in the open-circuit-voltage. An increase in the number of In
0.4
Ga
0.6
As layers leads to a proportional increase in the recombination rate, which is expressed in a proportional increase in the “saturation” current and corresponds to the model proposed in the study.
Abstract
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 shifted to the base and the emitter. As a result, it has been shown that the solar cell with a quantum dot array shifted to the base demonstrates the smallest open-circuit voltage drop and, accordingly, a higher efficiency value.
We present study of structural and optical properties of InP/GaInP quantum (QDs) providing a weak quantum confinement and creating a platform to study Wigner localization (WL) effects using high ...spatial resolution optical spectroscopy. Self-organized QD structures were grown using metal-organic chemical phase epitaxy by using different substrate misorientations and cap layer deposition temperatures. Using transmission electron microscopy and energy dispersive x-ray spectroscopy, we demonstrated a bimodal height distribution with peaks at ~5 and ~20 nm and a control of both the lateral size distribution, peaked from ~100 to ~160 nm, and the amount of Ga-In intermixing in the QDs (up to 20%). Using photoluminescence (PL) spectroscopy in combination with circular polarization degree and time resolved micro-PL measurements, we demonstrated control of the emission energy, the intrinsic doping, and the emission decay of these In(Ga)P QDs. Using high-spatial-resolution near-field PL spectra and imaging of single dots, we demonstrated WL effects in dots having a population of up to nine electrons and a parabolic confinement down to ω0 ~ 1 meV. We performed a self-consistent calculation of exciton transitions using an effective mass, mean field theory with an isotropic elasticity model to describe the effect of Ga-In intermixing on the emission properties of these dots; and we used calculations of shell splitting, using mean field Hartree-Fock approach and calculations of electron density distribution using configuration interaction approach, to described effects of enhancement of WL in non-circular dots with hard-wall potentials.
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