Electron Devices on Piezoelectric Semiconductors: A Device Model

The effects of acoustic waves on the terminal characteristics of electron devices on piezoelectric semiconductors are considered. The piezoelectric displacement charge is regarded as a time- and space-vary ing perturbation of the doping density of the semiconductor. Incorpora- tion of this doping perturbation into the usual acoustically quiescent device model yields the acoustically perturbed characteristics. In par- tieular, the interaction of a surface acoustic wave with a fieldeffect transistor on GaAs is considered. Good agreement with experimental data is demonstrated. etal. (7) attempted to demonstrate a memory correlator using diodes in the SAW beam path on GaAs. Melloch and Wagers (SI circumvented the cause of failure of these devices by sit- uating the diodes outside the beam path, coupling the diodes to the SAW with fingersover the beam path, and have achieved encouraging results. This author has proposed a memory cor- relator structure, recently discussed by colleagues (7) as the design most appropriate for wide-band applications, in which reference waveform storage and subsequent correlation with the input signal are performed by FET's in a SAW beam path. In the present contribution, a new model for the acousto- electric interaction in electron devices such as diodes or FET's located in the acoustic beam path is developed. In this model, the primary effect of the acoustic wave is to create a piezo- electric displacement charge which is viewed as a change in effective doping density in the semiconductor. In addition, piezoresistive effects produce changes in doping density and in carrier mobility. The former piezoresistive effect is readily added to the piezoelectric displacement charge but is shown to