Additional phonon modes and close satellite valleys crucialfor electron transport in hexagonal gallium nitride

Conventional models of electron transport in hexagonal $GaN$ crystals predicting electron drift velocity peak value up to $3.2×107cm∕s$ at $140–220kV∕cm$ and a pronounced negative differential mobility at higher fields are revised. The new model is suggested accounting for the additional low-energy optical phonon modes $(∼26meV)$ and the satellite valley location close $(400meV)$ to the conduction band bottom. Electron scattering on these and conventional $(∼92meV)$ LO-phonon modes together with the fast intervalley exchange is shown to limit electron drift velocity (⁠$<1.9×107cm∕s$ at $T=300K$⁠), in excellent agreement with the time-of-flight experiment.