AlGaAs-GaAs Solar Cells Research Articles

Achieving Steady and Stable Energy from AlGaAsGaAs Solar Cells

The hetero junction operating as a solar cell is based on n GaAs p GaAs p Al0.75Ga0.25As. This paper investigates the influence of radiation electron ray on layers of hetero-junction AlGaAsGaAs. Long term operation in the radiation zone degrades solar cell power operating parameters and reduces overall cell’s life. The impact of radiation electron ray has been analyzed with various doses on layers of the AlGaAsGaAs hetero junction. V-A characteristics and parameters such as the photocurrent density (Jsc), voltage at open circuit (Voc) and energy conversion efficiency ( (η), are evaluated for different doses of electron radiations. It is shown that current and voltage decrease when irradiation doses increase. Further, Jsc and η parameters decrease proportionally to the increase of the electron radiation doses whereas Voc is only slightly decreased.

Heteroface Gallium Arsenide Solar Cells Electron Induced Degradation Analytical Model

A model is presented which allows the calculation of the electron induced degradation in heteroface AlGaAs-GaAs solar cells. The temperature dependence of the semiconductor parameters is also included. The radiation effects have been modeled by the minority carrier lifetime degradation. The best agreement with experimental results is obtained when the recombination center capture cross section in p-GaAs region has a value of 4 10-12cm2 and the introduction rate is set to 0.1 cm-1. An optimum thickness of the p-GaAs layer of 0.3μm has been found. In this geometry, the temperature variation of the efficiency has a coefficient of 32.2K which is consistent with experimental data.

Radiation-induced traps in low-energy proton-irradiated GaAs solar cells

Trapping centers produced by 250-keV, 400-keV, 700-keV, and 1.5-MeV proton irradiations at room temperature in AlGaAs-GaAs solar cells have been studied. The traps detected by deep-level transient spectroscopy are the same as those produced by electron irradiations, only their introduction rates are different. An introduction rate was determined for each trapping center at the various proton energies. The large concentration of the E4 trap suggests it is associated with a cluster-type defect.

High-efficiency GaAs solar cells

An updated review of the state of the art in the development of GaAs solar cells is provided, with emphasis on AlGaAs-GaAs cells suitable for space applications. A set of theoretically derived characteristics is given for this type of solar cell. Comparison of measured performance with theory shows excellent agreement. Data on the effects of radiation damage (high-energy electrons, protons, and neutrons) is also integrated into a form useful for evaluation purposes. Techniques for fabricating (AlGa)As-GaAs solar cells in quantities large enough for practical applications are discussed and are shown to have been demonstrated. The possibility of extending these techniques to the fabrication of very thin low-weight cells for space applications is also considered. Finally, the results obtained to date in the development of GaAs solar cells for applications requiring concentrated sunlight are reviewed, for terrestrial as well as for space applications. As a milestone toward the practical application of AlGaAs-GaAs solar cells in space systems, a brief account is provided on the development status of small experimental AlGaAs-GaAs solar-cell panels for specific space flights.

Effects of Low Temperature Periodic Annealing on the Deep-Level Defects in 200 KeV Proton Irradiated AlGaAs-GaAs Solar Cells

Low temperature thermal annealing (200 to 400 °C) has been shown to be effective in reducing densities of deep-level defects induced by proton irradiation in AlGaAs-GaAs solar cells. The purpose of this paper is to report our study of the effect of periodic thermal annealing on the deep level defects induced by the 200 keV proton irradiation. The AlGaAs-GaAs mesa diodes were initially irradiated at room temperature by 200 keV protons to a fluence of 1011 P/cm2, and were annealed at 200 °C, 300 °C, and 400 °C, respectively. The samples were repeatedly irradiated by the same proton fluence and then annealed at 200, 300, and 400 °C up to four irradiation and annealing cycles. The DLTS, C-V, and I-V measurements were made on these samples to determine the defect and recombination parameters as functions of proton fluence (1011 to 4×1011 P/cm2) and annealing temperature (200 to 400 °C). The results showed that densities of both electron and hole traps as well as recombination current decrease with increasing annealing temperature. For comparison, some samples were also irradiated once at a fluence of 1011, 2×1011, 3×1011, and 4×1011 P/cm2, and annealed at 200, 300, and 400 °C for six hours, respectively. No significant difference was found in defect density between the periodic and non-periodic annealed samples. The observed main electron trap was due to Ec-0.71 eV while the main hole trap was due to Ev+0.18 eV, for the 200 keV proton irradiated GaAs solar cells.

Deep-level defects, recombination mechanisms, and their correlation to the performance of low-energy proton-irradiated AlGaAs—GaAs solar cells

A detailed study of deep-level defects, recombination mechanisms, and performance characteristics in low-energy proton-irradiated AlGaAs-GaAs solar cells has been carried out for several proton energies (i.e., 50, 100, 200, and 290 keV) and fluences (i.e., 1010, 1011, 1012, and 1013p/cm2) using the deep-level transient spectroscopy (DLTS), current-voltage ( I-V ), capacitance-voltage ( C-V ), and the scanning-electron microscopy operating in electron-beam induced current (SEM-EBIC) methods. Important defect parameters such as densities and energy levels of defects, thermal emission rates and capture cross sections of electrons and holes in each trap level as well as hole diffusion lengths in n-GaAs LPE layer were determined from these measurements. It is shown that the forward bias dark current was dominated by the recombination of electron-hole pairs via the proton-induced deep-level defects in the junction space-charge region of the cell. The increase in the dark current is directly related to the increase of trap density with increasing proton fluence in the irradiated solar cells. A quantitative correlation between the measured defect parameters and the performance characteristics of the proton-irradiated AlGaAs-GaAs solar cells was obtained from this study.