Frequency and wave-vector dispersion of the microwave mobility of drifting electron gas in GaN

We have studied the high-frequency response of drifting electron gas on time- and spatial-dependent harmonic perturbation in frame of the exact solution of Boltzmann transport equation using Monte-Carlo method. It was demonstrated that results obtained by Monte-Carlo for the case of low-density electron gas differ from ones that are given by conventional hydrodynamic approach. It was found the region of frequencies and wave-vectors where negative microwave mobility is realized. The appearance of the relatively low-frequency region can be interpreted as a manifestation of the Cherenkov-like effect and higher-frequency regions as a manifestation of well-known optical phonon transit-time resonance.