Temperature- and Doping-Dependent Anisotropic Stationary Electron Velocity in Wurtzite GaN

The influences of temperature, dopant density, free-carrier density, and field orientation on the electron drift mobility and velocity-field relationship in wurtzite
c
-axis GaN are quantified by means of theoretical investigation. Electron velocity perpendicular to the growth plane is uniformly lower than that parallel to the growth plane for field strengths below 500 kV/cm, although anisotropy within the basal plane itself is found to be insignificant. The calculated low-field electron mobility is demonstrated to be consistent with recent Hall measurements over a range of dopant densities. Low-field mobility is enhanced under the influence of free-carrier densities above the background doping due to both increased screening of ionized impurities and a reduction in A1-LO phonon lifetime through the plasmon-phonon interaction.