Impact of bias-dependent RS and RD on gm in AlGaN/GaN HEMTs under high-field conditions

Abstract

In the present study, RS and RD under both low-field and high-field conditions were extracted using mobility calculations that incorporate various scattering mechanisms, including polarization Coulomb field (PCF) scattering. Significant differences were observed between the two field regimes; the increase in RS and RD under high-field conditions exceeds 30% compared to that under low-field conditions, and both RS and RD were found to increase as VGS decreased. By decomposing RS and RD into resistance components contributed by various scattering mechanisms, the observed behavior was mainly attributed to PCF scattering. To further investigate the relationship between PCF scattering strength and device geometry under high-field conditions, the PCF mobility for devices with varying Lg, W, and Lgs(gd) was calculated. Stronger PCF scattering was observed in devices with larger Lg, larger W, and smaller Lgs(gd). In addition, the difference in RS between low-field and high-field conditions was found to cause a relative variation in the extrinsic transconductance under high-field conditions of approximately 0.2%–51%. Therefore, the effect of PCF scattering on RS and RD should be considered during device design.