The instability of Al ₂ O ₃ /4H-SiC interface at various process temperatures and ambient is investigated by the annealing of Al ₂ O ₃ /4H-SiC in low vacuum conditions as well as in N ₂ environments. Atomic layer deposited Al ₂ O ₃ on a 4H-SiC substrate with 3, 6 and 10 nm of thicknesses is treated at 300, 500, 700 and 900 °C under the vacuum level of 10 ⁻¹ torr. The as-deposited and annealed structures are analyzed using x-ray photoelectron spectroscopy. It is hypothesized that the minute quantity of oxygen present in low vacuum conditions diffuses through thin layers of Al ₂ O ₃ and helps in forming SiO ₂ at the interface even at low temperatures (i.e. 300 °C), which plays a pivotal role in determining the electrical properties of the interface. It is also proved that the absence of oxygen in the ambient prevents the formation of SiO ₂ at low temperatures. Additionally, it is observed that Al–OH is present in as-deposited layers, which gradually reduces after annealing. However, at around 700 °C, the concentration of oxygen in the whole structure increases to maximum and reduces at 900 °C.

The carbon vacancy (V_C) is a prominent defect in as-grown 4H-SiC epitaxial layers for high power bipolar devices. V_C is electrically active with several deep levels in the bandgap, and it is an efficient “killer” of the minority carrier lifetime in n-type layers, limiting device performance. In this study, we provide new insight into the equilibration kinetics of the thermodynamic processes governing the V_C concentration and how these processes can be tailored. A slow cooling rate after heat treatment at ∼2000 °C, typically employed to activate dopants in 4H-SiC, is shown to yield a strong reduction of the V_C concentration relative to that for a fast rate. Further, post-growth heat treatment of epitaxial layers has been conducted over a wide temperature range (800–1600 °C) under C-rich surface conditions. It is found that the thermodynamic equilibration of V_C at 1500 °C requires a duration less than 1 h resulting in a V_C concentration of only ∼10¹¹ cm⁻³, which is, indeed, beneficial for high voltage devices. In order to elucidate the physical processes controlling the equilibration of V_C, a defect kinetics model is put forward. The model assumes Frenkel pair generation, injection of carbon interstitials (C_i's) from the C-rich surface (followed by recombination with V_C's), and diffusion of V_C's towards the surface as the major processes during the equilibration, and it exhibits good quantitative agreement with experiment.

Pulsed laser ablation is used to form high‐quality silicon‐doped β‐Ga₂O₃ films on sapphire by alternatively depositing Ga₂O₃ and Si from two separate sources. X‐ray analysis reveals a single crystallinity with a full width at half maximum for the rocking curve around the (−201) reflection peak of 1.6°. Silicon doping concentration is determined by elastic recoil detection analysis (ERDA), and the best electrical performance is reached at a Si concentration of about 1 × 10²⁰ cm⁻³, using optimized deposition parameters. It is found that a high crystalline quality and a mobility of about 2.9 cm² (V s)⁻¹ can be achieved by depositing Si and Ga₂O₃ from two separate sources. Two types of Schottky contacts are fabricated: one with a pure Pt and one with a PtO_x composition. Electrical results from these structures are also presented.