Positron lifetime measurements and Doppler-broadening spectroscopy were combined to investigate the defect properties during Cu diffusion in Te-doped GaAs. The diffusion of Cu was performed during an annealing step at 1100C under two different arsenic vapour pressures. The samples were quenched into room temperature water. During a subsequent isochronal annealing experiment, it was found that vacancy clusters were generated and grown, and finally they disappeared. The lifetime results showed that, in addition to deep positron traps of vacancy type, positron trapping with a lifetime close to the bulk value of 228ps occurs. The positron lifetime results gave direct evidence of positron localization at shallow traps in GaAs:Te. Due to the Cu contamination during the annealing process, the shallow trap was believed to be the CuGa2− double acceptor. The concentration of shallow traps was determined and found to be in good agreement with the concentration determined by Hall measurement. It decreased up to saturation with increasing annealing. The positron binding energy to these negative non-open volume trap centers was determined to be 79meV. It was found to be in agreement with the calculated value. Moreover, coincidence Doppler-broadening spectroscopy showed clearly that Cu atoms were bound in the direct vicinity of the observed vacancy-like defects. Theoretical calculations of momentum distribution predicted that one Cu atom incorporated into a Ga site surrounds the observed open-volume defects.

Identification of Defect Properties by Positron Annihilation in Te-Doped GaAs after Cu In-Diffusion. M.Elsayed, R.Krause-Rehberg, W.Anwand, M.Butterling, B.Korff: Physical Review B, 2011, 84[19], 195208