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Low temperature thermal annealing (200 to 400 Â°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 Â°C, 300 Â°C, and 400 Â°C, respectively. The samples were repeatedly irradiated by the same proton fluence and then annealed at 200, 300, and 400 Â°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 4Ã1011 P/cm2) and annealing temperature (200 to 400 Â°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, 2Ã1011, 3Ã1011, and 4Ã1011 P/cm2, and annealed at 200, 300, and 400 Â°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.
Date of Publication: Dec. 1981