Effect of device geometry on static and dynamic performance of AlGaN/GaN-on-Si high electron mobility transistor

Abstract

This paper discusses the effects of several geometric parameters in DC and RF performances of AlGaN/GaN high electron mobility transistors (HEMTs) grown on high-resistivity silicon substrates. Those parameters include the dependency of gate length (Lg), gate cap length (Lcap) and gate-to-source distance (Lgs). It is shown that decreasing Lg and Lgs can both improve maximum drain current and transconductance behaviors. The fabricated 50 μm wide GaN-HEMT exhibits the maximum drain current of 1 A mm−1 at Vg = 2 V and maximum extrinsic transconductance Gmmax of 240 mS mm−1. Besides, decreasing Lg and Lcap also provides the improvement on current gain frequency (fT) and maximum oscillation cut off frequency (fMAX). The fT of 40 GHz and fMAX of 55 GHz at Vds = 5 V are demonstrated by GaN-HEMT device featuring Lg of 200 nm, Lcap of 300 nm and Lgs of 1.2 μm, which can realize the compact solid-state power amplifier used in S and C band. However, gate-to-source distance has little effect on RF performance of AlGaN/GaN HEMTs. Those results compared in our study are not only very essential for accurate GaN-based HEMT device modeling and fabrication, but are also vital to better understanding of their device physics.