1/ $f$ 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 ( ) is extracted using the unified 1/ f noise model, whereas the interface trap density ( D\mathbf {it} ) is extracted using the high–low-frequency C – V method. After the TMAH treatment, N_{\mathbf {ot}} is found to have decreased from 5.40 \times 10^{\mathrm {\mathbf {19}}} to 2.50 \times 10^\mathrm \mathbf 19~\mathrmeV^\mathrm \mathbf -1 \mathrmcm^\mathrm \mathbf -3 , whereas D\mathbf {it}^{\vphantom {(}} is decreased from 2.8 \times 10^\mathrm \mathbf 12 to 1.1 \times 10^\mathrm \mathbf 11~\mathrmeV^\mathrm \mathbf -1 \mathrmcm^\mathrm \mathbf -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. [ABSTRACT FROM AUTHOR]