Effects of Cu diffusion on electrical properties of GaAs

We investigated semi-insulating GaAs samples produced by Cu diffusion into n-type starting material by means of thermally stimulated current (TSC) and photoconductivity (PC) measurements, We show that the Cu-diffusion changes the EL2 centre into a deep donor (T3) with a lower activation energy, 0.7 eV. Similar effects have been observed in MBE GaAs grown at low temperature. The PC quenching and recovery of the T3 trap are similar to those usually observed for EL2. We conclude that the deep donor is a complex centre involving As/sub Ga/. In addition, we observe the usual Cu acceptor levels Cu/sub A/ and Cu/sub B/ at E/sub v/+0.15 and E/sub v/+0.4 eV. The dynamics of optical quenching and thermal recovery of the TSC signal from the Cu levels suggest that they are neither related to EL2 nor two levels of the same Cu-related double acceptor.