Normally-off AlGaN/GaN HFET with p-type GaN Gate and AlGaN Buffer

1. Introduction

To break through the material limits of Silicon and to realize the drastic performance improvement needed to meet the severe requirements in the future, wide bandgap semiconductors such as SiC and GaN have attracted much attention. AlGaN/GaN HEMTs are generally promising candidates for switching power transistors due to their high breakdown strength and the high current density in the transistor channel giving a low on-state resistance. Further, there exists a high requirement for simulation tools to accurately predict device performance prior to fabrication because of the high inherent cost of the cut-and-try method. Additionally, there are strong polarization fields in the AlGaN/GaN material system (spontaneous and piezoelectric polarization). Failure to include this strong polarization field will introduce distortion to the calculated band diagrams and thus compromise simulation results. Those simulations helped in the understanding of basic physics in GaN HEMTs. Thus we have decided here to simulate and compare to experimental data a normally-off AlGaN/GaN HEMT with a p-type gate based on [1]. Indeed The inherent normally-on behavior of AlGaN/GaN HEMTs would exclude them from most power-electronic applications. The p-GaN gate transistors presented here combine the high-mobility 2DEG transistor channel with secure normally-off operation, as is required for applications in power electronics. However, the required Vth > +1 V is often achieved by a low Al-concentration in the AlGaN barrier, giving a reduced electron density in the 2DEG of the transistor channel and compromising RON. Here, a low Al-concentration AlGaN buffer beneath the GaN channel is introduced to gain both a high electron concentration in the 2DEG and a high Vth.