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

Abstract

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 (Not) 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, Not is found to have decreased from 5.40 x 10(19) to 2.50 x 10(19) eV(-1)cm(-3), whereas D-it is decreased from 2.8 x 10(12) to 1.1 x 10(11) eV(-1)cm(-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.