Influence of electron mobility modeling on DC I-V characteristics of WZ-GaN MESFET

We report on the drift-diffusion based simulation of a wurtzite (WZ) GaN MESFET. The main emphasis is put on the influence of electron mobility modeling on DC current-voltage (I-V) characteristics of the WZ-GaN MESFET. Two different analytical expressions are used for the electron mobility as a function of electric field. The first model is based on a simple saturation of the steady-state drift velocity with electric field (conventional three-parameter model). The other model is more realistic since it well reproduces the drift velocity-field characteristics obtained by Monte Carlo (MC) calculations, revealing the peak drift velocity with subsequent saturation at higher electric fields. Thus, it should be implemented in the drift-diffusion model for a following device simulation. However, the MC electron transport data for WZ-GaN are influenced by the specific choice of the material and band structure parameters, resulting in a variation of drift velocity-field characteristics. In addition, it should be noted that the MC simulation also neglects crystal defects in GaN, which, for example, might lead to uncontrolled electron compensation and additional electron scattering. In the present study we show that the DC I-V characteristics of the WZ-GaN MESFET are strongly affected by the MC-like electron mobility model, in particular by the peak steady-state velocity and the shape of the velocity-field characteristics even for the same drift velocity saturation level.