Interface charge engineering on an in situ SiN_x/AlGaN/GaN platform for normally off GaN MIS-HEMTs with improved breakdown performance

This work adopts interface charge engineering to fabricate normally off metal-insulator-semiconductor high electron mobility transistors (MIS-HEMTs) on an in situ SiN_x/AlGaN/GaN platform using an in situ O₃ treatment performed in the atomic layer deposition system. The combination of in situ SiN_x passivation and an O₃-treated Al₂O₃/AlGaN gate interface allows the device to provide an excellent breakdown voltage of 1498 V at a low specific on-resistance of 2.02 mΩ cm². The threshold voltage is increased by 2 V by significantly compensating the net polarization charges by more than five times with O₃ treatment as well as reducing the interface traps and improving the high-temperature gate stability. Furthermore, a physical model of fixed charges at the Al₂O₃/AlGaN interface is established based on dielectric thickness-dependent linear fitting and numerical calculations. The matched device performance and simulated energy band bending elucidate the O₃-treated fixed-charge modulation mechanism, providing a practical method for producing normally off GaN MIS-HEMTs.