Amplification of Hypersound in GaN Films

The excitation of hypersonic waves (f =50 - 200 GHz) due to its coupling with amplified space charge waves in GaN films is theoretically researched. An amplification of space charge waves due to negative differential conductivity in GaN films on semi-infinite substrate is considered and spatial increments are obtained. The amplified space charge waves can excite hypersonic waves at the same frequency due to piezoeffect and deformation potential mechanisms. It is also demonstrated that the piezoeffect is very effective for resonant excitation of hypersonic waves in the case of full mechanic contact of GaN film and nonpiezoelectic substrate.