Al2O3/in situ GaON gate dielectrics incorporated GaN MIS-HEMTs with stable VTH and significantly reduced interface state density

This work reports a metal–insulator–semiconductor High-Electron-Mobility-Transistor (HEMT) with Al2O3/in situ GaON bi-layer gate dielectric for improved threshold voltage (VTH) stability and reduced interface state density. With a combination of in situ GaON and large bandgap Al2O3 on top of the recessed gate region, normally-off HEMT was achieved with high On/Off current (ION/IOFF) ratio of 109, low VTH hysteresis less than 60 mV, and low-interface trap density (Dit) in the range of 4 × 1011–2 × 1012 cm−2·eV−1. Thanks to the sharp GaN/oxide interface with narrow distribution of lattice constant, uniform strain distribution and significantly reduced trap density were obtained. More importantly, our proposed bi-layer gate dielectric is perfectly compatible with the conventionally utilized gate recessing technique compared to the conventionally utilized in situ SiNx, demonstrating itself as a promising candidate in GaN power devices.