Investigation Of Electron Mobility And Saturation Velocity Limits In Gallium Nitride Using Uniaxial Dielectric Continuum Model

Here we introduce a uniaxial dielectric continuum model with temperature-dependent phonon mode frequencies to study temperature-and orientation-dependent polar-optical-phonon limited electron mobility and saturation velocity in uniaxial semiconductors. The formalism for calculating electron scattering rates, momentum relaxation rates, and rate of energy change as a function of the electron kinetic energy and incident electron angle with respect to the c-axis are presented and evaluated numerically. Electron-longitudinal-optical-phonon interactions are shown to depend weakly on the electron incident angle, whereas the electron-transverse-optical-phonon interactions around the emission threshold energy are observed to depend strongest on the electron incident angle when varied from pi/4 to pi/2 (with respect to the c-axis). We provide electron mobility and saturation velocity limits in different GaN crystal orientations as a function of temperature and electron concentration. At room temperature and for an electron density of 5 x 10(18) cm(-3), electron mobility limit of similar to 3200 cm(2)/V s and electron saturation velocity limit of 3.15 x 10(7) cm/s are calculated. Both GaN electron mobility and saturation velocity are observed to be governed by the longitudinal-optical-phonon interaction, and their directional anisotropy is shown to vary less than 5% as the electron incident angle with respect to the c-axis is varied from 0 to pi/2. Overall, we develop a theoretical formalism for calculating anisotropic properties of uniaxial wurtzite semiconductors. Published by AIP Publishing.