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.
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.
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 current–voltage characteristics of In
x
Ga
1 –
x
As/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/cm
2
. Values exceeding 85%, achieved for the quantum efficiency, indicate that the “memory” and tellurium segregation effects characteristic of this kind of impurity are suppressed.
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 cm
2
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 mm
2
square) series resistance was 0.16 Ω. Optical power 270 mW at current 1.5 A has been achieved.
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.
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 Al
0.9
Ga
0.1
As/Al
0.1
Ga
0.9
As Bragg heterostructure and an Ag mirror layer. Light-emitting diodes with the external quantum efficiency EQE = 37.5% at current densities greater than >10 A/cm
2
have been fabricated.
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.
Heterostructures with embedded layers of single InAs and In0.8Ga0.2 As quantum dots (QDs) in a GaAs matrix have been obtained by metalorganic vapor-phase epitaxy. The photoluminescence spectra of ...these QDs have been measured in a wide temperature range and the analysis of the photoluminescence peaks behavior has been carried out. As a result, it have been found that the In0.8Ga0.2 As QDs has better size uniformity and contains a smaller number of defective islands in comparison with InAs QDs.
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