8.3 High-Performance Normally-off GaN MIS-HEMTs with Dual Gate Insulator employing PEALD SiNx Interfacial Layer and RF-sputtered HfO2

To fabricate high-performance GaN MIS-HEMTs, we have employed a novel SiNx/HfO2 dual gate insulator. A PEALD technique was used for very thin high quality SiNx (5 nm) as an interfacial layer, followed by RFsputtered HfO2 as a high-k dielectric for the second gate insulator structure. As a result, we have achieved excellent characteristics such as small subthreshold slope of 85 mV/dec, extremely small off-state drain leakage current less than 10 -9 A/mm and high ON/OFF drain current ratio of ~10 9 , and low ON-state resistance of 1.79 and 1.84 mΩ•cm 2 for normally-on and normally-off devices, respectively. C-V hysteresis was negligible for normally-on device, but for normally-off device 300 mV was observed. Finally, in normally-off device, a large threshold voltage of 1.65 V, and a high breakdown voltage of 900 V when ID was defined for 0.1 μA/mm were achieved.