Optimization of Dynamic Source Resistance in a β-Ga2O3 HEMT and Its Effect on Electrical Characteristics

Abstract

The increase of bias-dependent source access resistance, rs, with high gate bias is attributed to a sharp drop in transconductance, gm, and current gain cut-off frequency, fT, of high-electron-mobility transistors (HEMTs). Consequently, source and drain implant regions (n++ cap regions) are commonly used to obtain expected results in experimental devices as predicted theoretically. This paper investigates the effect of different doping profiles in n++ cap regions using a finite space in access regions on gm and fT with increasing bias. The device under test (DUT) is a beta-gallium oxide (β-Ga2O3)-based HEMT using an AlN barrier to create polarization-induced two-dimensional electron gas (2DEG). Dynamic access resistance is optimized by lateral Gaussian n++ doping characteristics using a finite gap between the ohmic contacts and barrier layer, which ensures high RF device performance. The technology computer-aided design (TCAD) simulation results for source access resistance are validated with an appropriate analytical model. It is observed that the peak electric field in the source access region can be controlled to delay electron velocity saturation, which yields higher mobility and reduced access resistance.