EL2 DEEP DONOR STATE IN SEMIINSULATING GAAS REVEALED BY FREQUENCY-DEPENDENT POSITRON MOBILITY MEASUREMENTS

Positron mobility measurements carried out on semi-insulating GaAs, using the Doppler shift in annihilation radiation technique, show a sharp transition from a high mobility value ∼120 cm2 V-1 s-1 to a lower value ∼45 V-1 s-1 just below room temperature. The temperature of the transition is found to be dependent on the frequency of the applied AC bias. We show that this effect is an artifact due to the thermal ionization of the EL2 deep donor state, which in its ionized state forms a positive space charge that causes the positron to experience large electric fields. This observation suggests a new positron annihilation-based deep-level transient technique applicable to semi-insulating materials. © 1994 The American Physical Society.