Hopping conduction and piezoelectricity in Fe-doped GaN studied by non-contacting resonant ultrasound spectroscopy

Using the antenna-transmission acoustic-resonance technique, we measured temperature dependencies of mechanical resonance frequencies and attenuation of an Fe-doped GaN. A strong internal-friction peak appears during temperature change, at which reduction in frequency occurs. The peak temperature rises as frequency increases, indicating the phonon-assisted hopping conduction of carriers between Fe centers. The Arrhenius plot yields the activation energy of the hopping conduction to be 0.23 ± 0.05 eV. The frequency reduction of a quasi-plane-shear resonance mode yields the piezoelectric coefficient e15 = 0.332 ± 0.03 C/m2.