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As the p-type doping β-Ga2O3 is absent up to now, metal gate (MG) stacks with high work functions are expected to benefit the fabrication of normally- OFF β-Ga2O3 transistors. In this article, the electrical characteristics of β-Ga2O3 metal-electrode-gated metal–oxide–semiconductor (MOS) devices with Al-rich HfAlO dielectrics and different MG stacks (Ni, Au, Pt, and Ti) are evaluated. The interface state density (Dit) of HfAlO/β-Ga2O3 interface is characterized based on the frequency-dependent capacitance–voltage (C − V) and photo-assisted deep ultraviolet (DUV) C − V measurements. An average Dit of 4.45 × 1011 eV−1 cm−2 is extracted from the photo-assisted (deep UV) C − V measurement, while a large amount of border traps, negative fixed charges, and deep traps is also induced at the oxide layer and/or HfAlO/β-Ga2O3 interface. Then, this article investigates the evaluations of Ti, Ni, Au, and Pt as candidate MGs for β-Ga2O3 MOS using Al-rich HfAlO as gate dielectric. The obvious flat-band voltage (VFB) shift and gate leakage variation are observed in β-Ga2O3 capacitors with different MG solutions, indicating that HfAlO dielectric combined with Ni, Au, and Pt MGs is promising to facilitate some beneficial modifications of normally- OFF β-Ga2O3 transistors, while Ti electrode is more suitable for normally- ON β-Ga2O3 transistors. This article provides an additional practical guideline for choosing the appropriate MG stacks and potential gate dielectric to the development of normally-OFF Ga2O3 transistors. [ABSTRACT FROM AUTHOR]

An improved Bosch etching process using inductively coupled plasma system has been investigated for the etching of 4H-silicon carbide (SiC). By optimizing the etch parameters, a mesa structure with nearly vertical sidewall and without microtrench at the bottom corner has been fabricated, and the formation and elimination of the microtrench are preliminarily discussed for the Bosch cycles in this paper. Scanning electron microscopic analysis was used to demonstrate the etched morphology under different etching conditions. Simple mesa-terminated 4H-SiC p-i-n diodes were fabricated. The effect of the improved mesa structure on the dc characteristics of the diodes has been experimentally verified by comparing with the nonoptimized mesa structure with microtrench. The results exhibited a completely consistent forward tendency and a similar reverse leakage level less than −900 V for both diodes, but different blocking performances. A maximum blocking voltage of 1565 V at room temperature was obtained from the nonmicrotrenched device with a mesa height of 4.3 \mu \textm , corresponding to 66% of a parallel plane breakdown voltage for the drift layer of 15 \mu \textm . Slight microtrench is the main cause of premature breakdown. [ABSTRACT FROM AUTHOR]