Acoustoelectric charge injection in semiconductors

A considerable change of trapped and free electric charge is observed in piezoelectric semiconductors in the presence of a traveling acoustic wave. The electric field, induced by the ultrasound, alters the electric equilibrium of the semiconductor sample, resulting in an accumulation of majority carriers at the surface with a consequent decrease in surface resistance. In specific cases, charge injection occurs at the semiconductor-metal contact area due to the large electric field induced by the acoustic wave. This effect, here referred to as the Acoustoelectric Charge Injection, was also investigated for the case in which a Surface Acoustic Wave (SAW) is propagating along the metalized surface of a semiconductor. The injected charge is experimentally measured having a exponential time decay typical of a deep trap level, thus suggesting that Acoustic Charge Injection can modify the transient behavior of high-speed analog signal processing devices based on SAW, acoustooptic, and acoustic charge transport (ACT) phenomena. Experimental results and theoretical calculations are presented for CdS samples and for a metalized GaAs-epilayer grown on semi-insulating GaAs substrate.<>