Nonlinear interaction of acoustic surface waves with carriers

We calculate the 2nd-order signal generation due to the space-charge nonlinearity induced by two interacting surface waves in a piezosemiconducting material. Using the Bleustein¿Gulyaev mode as a typical example, it is shown that this 2nd-order term is not zero for two oppositely travelling surface waves of the same frequency ¿ in the absence of electron drift. This calculation clearly shows that this nonzero signal arises from the decrease in the ultrasonic electric field toward the interior of the sample. The general result can be extended easily to other types of elastic surface waves. Complementary experiments are also reported on the interaction of surface waves propagating in the same direction, and it is shown that there is a satisfactory agreement between the experimental data and the results of the analysis.