Enhanced backward-wave generation in silicon

A large enhancement of the parametrically generated backward-propagating elastic wave in Si: In is reported. The enhancement is observed when the nonlinear interaction between microwave electric and elastic fields occurs at the interface between the Si sample and the sputtered thin-film ZnO ultrasonic transducer. Phase and spectral information is presented. No satisfactory mechanism for the enhancement is known. © 1982 The American Physical Society.