Low temperature annealing of deep electron traps produced by proton irradiation of n-GaAs

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Abstract
By reverse-bias capacitance-voltage measurements on Schottky diode samples the authors have determined the immobile-charge concentrations N+ at 85 K and 120 K on n-type VPE GaAs, before and after 1.0 MeV proton irradiation at the low temperature and after progressive heating to 300 K, so as to study the proton-irradiation-induced defects that anneal at low temperatures in this semiconductor and to obtain information on their carrier-trapping energy levels. They find that the irradiation-induced decrease in the N+ value is considerably removed, by a total of about 40%, in three defect-annealing stages, A, B and C, centred at approximately 180, 235 and 280 K respectively. The annealing kinetics of stages B and C are consistent with those of the annealing stages I and II found by Thommen (1970) in studies of resistivity changes in electron-irradiated bulk n-GaAs. In contrast, they report stage A as a new annealing stage at a temperature lower than any previously known for defects in gallium arsenide. By consideration of the sensitivity of the N+ value at low measurement temperature to the natures and energy levels of electron trapping defects they deduce that the three stages A, B and C are all predominantly due to the removal of acceptor levels that lie below about Ec-0.2 eV. They deduce also that the stage C levels are close to or below the middle of the energy-band gap. They suggest that the stage A, B and C defects may include defects produced by the displacement of gallium atoms.