Anisotropic longitudinal electron diffusion coefficient in wurtzite gallium nitride

The longitudinal electron diffusion coefficient (D l ) of wurtzite (WZ) gallium nitride (GaN) is calculated by an ensemble Monte Carlo (EMC) method. By using the power spectral density associated with velocity fluctuation, the relationship between D l and electric field strength, frequency, doping concentration and temperature is presented. The anisotropic D l of GaN impacted by anisotropy of the electronic dispersion is also investigated. It has been found that the D l in Γ–A direction (c-direction) is larger than that in Γ–M direction (basal plane) in most cases. For lower electric field, the D l keeps constant at first, then decreases with increasing frequency. However, for higher electric field, the D l firstly approaches a peak value, then decreases with increasing frequency. When the frequency is zero, the D l decreases with the increasing electric field, and then increases until a peak value. Finally, it decreases with increasing electric field again. When the temperature increases, the D l decreases in both directions for increasing scattering rate. A comparison between our calculated diffusion coefficient and the mobility under low electric field by Einstein equation is presented.