Fig. 1. Schematic cross section of recess-gate Al₂O₃/AlGaN/GaN MOS-HEMTs.

Fig. 2. (a)-(b) Cross-sectional TEM micrographs of recess-gate Al₂O₃/AlGaN/GaN MOSHEMTs and (c)–(d) the enlarged view at Al₂O₃/GaN interface: (a) sample 1# with DCIO and wet etch post-etch surface treatment and (b) the controlled sample 2#.

Fig. 3. Influence of post-etch surface treatment on normally-off Al₂O₃/AlGaN/GaN MOS-HEMTs in terms of (a) transfer and transconductance characteristics and (b) breakdown characteristics.

Fig. 4. Sequential C–V hysteresis curves of Al₂O₃/AlGaN/GaN MOS-HEMTs (a) without and (b) with DCIO treatment and wet etch.

Fig. 5. Voltage shift due to (a) interface traps and (b) border traps as a function of program voltage for normally-off Al₂O₃/AlGaN/GaN MOS-HEMTs.

Fig. 6. (a) Typical photo-assisted C–V characteristics of normally-off MOS-HEMTs before and after light illumination with different wavelength. (b) Gate voltage at C = 150 nF/cm² as a function of wavelength varying from 500 nm to 360 nm. The lower and upper dashed lines for each device show the reference voltage level under dark before and after trap filling.

Fig. 7. State density distribution of border traps in normally-off MOS-HEMTs with and without DCIO treatment and wet etch.