Numerical analysis of short‐gate GaN HEMTs with Fe‐doped buffer layers

Abstract

AbstractThe influence of Fe‐doped GaN buffer layers on microwave GaN HEMT performance was analyzed using a two‐dimensional numerical model. The device structure model was based on a fabricated Ka‐band AlGaN/GaN HEMT with a 0.2‐µm gate. Deep acceptors brought about by Fe doping were introduced in the GaN buffer layer model, and the concentration profile was based on the Fe concentration profile measured by SIMS. The slow turn‐off of Fe doping was taken into account. The simulated drain current showed a sharp current‐off in the 0.2‐µm gate device, and it was found that this characteristic was influenced by the slow turn‐off Fe‐doping profile. To discuss the effect on drain current collapse in high‐frequency large‐signal operation, ionized deep acceptor concentrations were simulated and compared between the on‐state and off‐state. The results showed that the ionized concentration increases in the off‐state in the area of slow turn‐off Fe‐doping. It is expected that the ionization is one of the causes of drain current collapse in the 0.2‐µm gate device. The simulated results also indicated enhanced collapse in the 0.2‐µm gate device in comparison with the results for a 0.6‐µm gate device (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)