Resonant Amplification and Coupling of Acoustic Surface Waves With Electrons Drifting Across a Magnetic Field

We show that acoustic surface waves on a piezoelectric can be resonantly amplified by coupling to a weakly damped carrier surface wave on an adjacent semiconductor in which the conduction electrons are made to drift across an applied magnetic field. The conditions for such a wave-wave interaction are established, and calculations of the growth rate and its characteristics are given. Under the same conditions, reversing the direction of the magnetic field changes the amplifier to an almost loss-free, tunable, coupler.