Controlled oxide interlayer for improving reliability of SiO₂/GaN MOS devices

Abstarct The impact of controlling Ga-oxide (GaO x ) interlayers in SiO2/GaO x /GaN gate stacks is investigated by means of physical and electrical characterizations. Direct deposition of SiO2 insulators produces thin GaO x interlayers, and subsequent oxidation treatment attains high-quality insulator/GaN interface. However, the Ga diffusion into the SiO2 layers severely degrades the breakdown characteristics of GaN-MOS devices. To improve reliability of such devices, we proposed a two-step procedure with the initial SiO2 deposition conducted under nitrogen-rich ambient, followed by thick SiO2 capping. We found that this two-step procedure enables nitrogen incorporation in the insulator/GaN interface to stabilize GaN surface. Consequently, the Ga diffusion into the SiO2 overlayer during the oxidation annealing is effectively suppressed. The proposed method allows us to achieve a SiO2/GaO x /GaN stacked structure of superior electrical property with improved Weibull distribution of an oxide breakdown field and with interface state density below 1010 cm−2 eV−1.