AlGaN/GaN devices for future power switching systems

GaN/AlGaN device technologies are presented aiming at the applications to power switching systems. In order to reduce on-resistance (R_on), we developed SL (super lattice) capping and QA (quaternary alloy) over-layer techniques for GaN/AlGaN HFET. Further, we achieved almost the same mobility keeping the same 2DEG density for GaN/AlGaN hetero structure grown on Si (111) substrates, which will make the cost comparable to conventional Si one. The experimentally obtained R_onA of the FET is 1.9 mOmegacm², which is 14 times lower than that of Si ones. Additionally, a novel approach to realize enhancement-mode operation of GaN/AlGaN FET is examined over R-plane sapphire, where non-polar AlGaN/GaN heterostructure, free from polarization charge, can be grown

Introduction

Besides microwave or milliwave transmitter application, GaN/AlGaN devices potentially have wide range of power electronics application below GHz. Increasing demand of higher switching frequency with lower loss operation, GaN/AlGaN FETs become viable alternative to silicon power MOS or IGBT. Owing to the inherent nature of wide bandgap characteristics, GaN/AlGaN FETs have extremely high blocking-voltage with high current handling capability per unit area, as schematically shown in fig. 1. Fig. 1 Typical I-V Characteristics of FETs made of Si, GaAs, and GaN/AlGaN at the same gate length of 0.5 um.