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 acousti c wave. The electric field, induced by the ultrasound, alters the elec tric equilibrium of the semiconductor sample, resulting in an accumula tion 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 held induc ed by the acoustic wave. This effect, here referred to as the Acoustoe lectric Charge Injection, was also investigated for the case in which a Surface Acoustic Wave (SAW) is propagating along the metalized surfa ce of a semiconductor. The injected charge is experimentally measured having a exponential time decay typical of a deep trap level, thus sug gesting that Acoustic Charge Injection ran modify the transient behavi or of high-speed analog signal processing devices based on SAW, acoust ooptic, and acoustic charge transport (ACT) phenomena. Experimental re sults and theoretical calculations are presented for CdS samples and f or a metalized GaAs-epilayer grown on semi-insulating GaAs substrate.