A study of the electric field transient at the Au/semi-insulating GaAs contact under an alternating current square-pulse bias

Positron lifetime spectroscopy combined with a 50 V AC applied square-wave bias has been used to probe the electric field in the 2 gm region next to an Au/SI-GaAs contact. The electric fields spatially and time averaged over the reverse half-period at different temperatures (255-295 K) and pulsing periods (similar to1 ms-10 ks) have been obtained using a numerical differentiation technique. It is found that within the temperature range studied, the electric field first increases as a function of time to a maximum of about 10 kV cm(-1) and then decreases, before finally saturating at the DC value of 7 kV cm(-1). The increase of the electric field with time is attributed as previously to the electron emission from the EL2 defect. The subsequent electric field decrease is associated with the onset of a thermally activated process with an energy barrier of 1.03 +/- 0.15 ev This process, which causes the neutralization of the. space charge region, may be tentatively attributed to the recombination centres EL5 or EL6.