In this study, we investigated the effects of postmetallization annealing (PMA) on the interface properties of GaN metal-oxide-semiconductor (MOS) structures using Al 2 O 3 prepared by atomic layer deposition. Excellent capacitance-voltage (C-V ) characteristics without frequency dispersion were observed in the MOS sample after PMA in N 2 ambient at 300-400 °C. The PMA sample showed state densities of only at most 4 ' 10 10 cm %1 eV %1 . A geometric phase analysis of transmission electron microscopy images after PMA revealed a uniform distribution of the lattice constant near the Al 2 O 3 /GaN interface, leading to the improved bond termination and bonding order configuration along the interface.

The proposal and processing aspects of the prove-of-concept InGaN/GaN/AlGaN/GaN metal-oxide-semiconductor (MOS) high-electron mobility transistor with etched access regions are addressed. Full strain and decent quality of the epitaxial system comprising 4 nm In 0.16 Ga 0.84 N/3 nm GaN/5 nm Al 0.27 Ga 0.73 N are observed using a high-resolution transmission-electron microscopy and by deformation profile extractions. Large negative polarization charge in the MOS gate stack provides the HEMT normally-off operation, while free electrons are populated at access regions after etching. Consecutive passivation by 10 nm Al 2 O 3 together with annealing at 300 °C improved the Al 2 O 3 /semiconductor interface, with the threshold voltage (V T ) reaching 1 V. Improvements of the present concept in comparison to the previous one with a gate recess were proved by showing the decreased drain leakage current and increased breakdown voltage.