Compositional dependence of longitudinal sound velocities of piezoelectric (111) [In.sub.x][Ga.sub.1-x]As measured by picosecond ultrasonics

Picosecond ultrasonic experiments were performed to generate and detect acoustic pulse in piezoelectric (111) epilayers of [In.sub.x][Ga.sub.1-x]As. It was found that the sound velocity exhibits an obvious bowing with different alloy compositions and supports a nonlinear compositional dependence of the elastic constants of [In.sub.x][Ga.sub.1-x]As.