Mode switching of acoustic phonons by external bias

We experimentally manifested a new type of transverse acoustic (TA) phonon generation and its amplitude control by external reverse bias in c-axis grown from InGaN/GaN diode structures, in clear contrast to the well-established conditions for longitudinal acoustic (LA) phonon generations. The generation and propagation dynamics were investigated by analyzing the dynamic Fabry-Perot interferences and, based on the twisted energy band structure, we have confirmed that the lateral electric fields under reverse bias broke the in-plane isotropy of c-GaN resulting in TA mode generation.