1/ Noise Characteristics of Surface-Treated Normally-Off Al2O3/GaN MOSFETs

Normally off Al₂O₃/GaN MOSFETs are fabricated with a tetramethylammonium hydroxide (TMAH) treatment as a postgate recess etch. The effects of the surface treatment on the etched GaN surface are investigated using low-frequency (1/f ) noise and capacitance-voltage (C-V) measurements. For a quantitative comparison with conventional devices, the oxide trap density (N_ot) is extracted using the unified 1/f noise model, whereas the interface trap density (D_it) is extracted using the high-low-frequency C-V method. After the TMAH treatment, N_ot is found to have decreased from 5.40 × 10¹⁹ to 2.50 × 10¹⁹ eV^-1cm^-3, whereas D_it is decreased from 2.8 × 10¹² to 1.1 × 10¹¹ eV^-1cm^-2, as compared with conventional devices. The surface treatment is thus shown to lower trap density in the Al₂O₃/GaN MOSFETs by smoothing the surface and suppressing plasma damage in the recessed GaN surfaces.