Piezoelectric coefficients of GaN determined by hopping conduction of carriers

Abstract

Using resonant ultrasound spectroscopy, we monitored the resonance-frequency and internal-friction behaviors of a GaN monocrystal at elevated temperatures. An internal-friction peak appears with increasing temperature, at which reduction of frequency occurs. The frequency shift reflects the disappearance of the apparent piezoelectricity due to hopping conduction of carriers, allowing us to accurately determine the piezoelectric coefficients eij. We measured the frequency decrements of eight vibrational modes to inversely determine three independent eij: Our values are e15=−0.22±0.02 C/m2, e31=−0.14±0.02 C/m2, e33=1.15±0.05 C/m2.