The intrinsic deep donor level, known as EL2, is responsible for semi-insulating behavior of undoped GaAs. EL2 is the most extensively studied point defect in GaAs. The most important property related to EL2 is the metastability under sub-bandgap light exposure at low temperature. The microscopic origin of EL2 and its photo-induced metastability is still under debate. We present an experimental investigation on unirradiated and irradiated semi-insulating GaAs using thermally stimulated current spectroscopy and photo-current quenching. In addition to EL2, we have discovered some other metastable defects in semi-insulating GaAs. Li ions of 48 MeV were used to irradiate semi-insulating GaAs with fluences between 1011and 1013ions/cm2. The energy loss of 48 MeV Li ions in GaAs is dominantly due to electronic processes because the energy loss due to nuclear collision processes is much less than the lattice binding energy of GaAs. Extended range of 48 MeV Li ions in GaAs has been used to modify the defect levels by electronic energy loss processes. Several modifications of defect levels, including the metastable levels in semi-insulating GaAs observed after irradiation, are discussed. © 2003 Elsevier B.V. All rights reserved.
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