Shallow positron traps in GaAs

Positron annihilation in GaAs at low temperatures has been studied with positron-lifetime and diffusion-length measurements. The lifetime results show that in addition to vacancy-type deep traps, positron trapping with a lifetime very close to the bulk value of 230 ps occurs below 200 K. This is observed together with a strong decrease in the positron-diffusion length from 1500 to 800 A\r{} measured with a slow-positron beam. The results give direct evidence on positron localization at shallow traps in GaAs. A Rydberg state around a negative point charge is suggested for the origin of the shallow trap. The detrapping analysis of both lifetime and diffusion-length data yields a binding energy of 43\ifmmode\pm\else\textpm\fi{}5 meV for the positron bound to these negative centers. This value is in good agreement with the binding energies of electrons and holes to the shallow levels in GaAs.

Перевод пока недоступен