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Polarization engineering is a promising approach to achieve high positive threshold voltage (Vth) in GaN-based metal-oxide-semiconductor high electron mobility transistors (MOS HEMTs). In this paper, we investigate all critical interfaces of polarization-engineered normally-off Al2O3/InGaN/AlGaN/GaN MOS HEMTs using transmission electron microscopy and X-ray photoelectron spectroscopy. Mechanisms of threshold voltage ( V TH ) instabilities are also analyzed. Devices were subjected to positive-bias stress-recovery experiments to capture the transient change in Vth. We propose a model that explains observed peculiar behavior and discuss the role of 2-dimensional hole gas (2DHG) in Al2O3/InGaN/AlGaN/GaN MOS HEMTs Vth shift.

International audience; Al, Au, Ti/Al and Ti/Au contacts were prepared on n-GaN and annealed up to 900 °C. The structure, phase and morphology were studied by cross-sectional transmission and scanning electron microscopy as well as by X-ray diffraction (XRD), the electrical behaviour by current–voltage measurements. It was obtained that annealing resulted in interdiffusion, lateral diffusion along the surface, alloying and bowling up of the metal layers. The current–voltage characteristics of as-deposited Al and Ti/Al contacts were linear, while the Au and Ti/Au contacts exhibited rectifying behaviour. Except the Ti/Au contact which became linear, the contacts degraded during heat treatment at 900 °C. The surface of Au and Ti/Au contacts annealed at 900 °C have shown fractal-like structures revealed by scanning electron microscopy. Transmission electron microscopy and XRD investigations of the Ti/Au contact revealed that Au diffused into the n-GaN layer at 900 °C. X-ray diffraction examinations showed, that new Ti2N, Au2Ga and Ga3Ti2 interface phases formed in Ti/Au contact at 900 °C, new Ti2N phase formed in Ti/Al contact at 700 and 900 °C, as well as new AlN interface phase developed in Ti/Al contact at 900 °C.

Al (150 nm)/Ti (30 nm) contacts have been successively deposited onto p-type 6H–SiC wafers. The layer structure has been annealed at 900 °C for 4 min. The annealed contacts are Ohmic. The structure of the annealed contact layers was identified as a Ti 3 SiC 2 layer on SiC and covered by an Al 3 Ti layer. Both layers and phases are formed as a result of solid phase interaction between the metallic layers and SiC, and are epitaxial to the 6H–SiC. Ti 3 SiC 2 is suggested as a new contact material to p-type SiC, which promises high temperature stable contacts due to its excellent properties.