Ultra-wide bandgap beta-gallium oxide (β-Ga2O3) has been attracting considerable attention as a promising semiconductor material for next-generation power electronics. It possesses excellent material properties such as a wide bandgap of 4.6–4.9 eV, a high breakdown electric field of 8 MV/cm, and exceptional Baliga’s figure of merit (BFOM), along with superior chemical and thermal stability. These features suggest its great potential for future applications in power and optoelectronic devices. However, the critical issue of contacts between metal and Ga2O3 limits the performance of β-Ga2O3 devices. In this work, we have reviewed the advances on contacts of β-Ga2O3 MOSFETs. For improving contact properties, four main approaches are summarized and analyzed in details, including pre-treatment, post-treatment, multilayer metal electrode, and introducing an interlayer. By comparison, the latter two methods are being studied intensively and more favorable than the pre-treatment which would inevitably generate uncontrollable damages. Finally, conclusions and future perspectives for improving Ohmic contacts further are presented.

Atomic-layer-deposition (ALD) of In2O3 nano-films has been investigated using cyclopentadienyl indium (InCp) and hydrogen peroxide (H2O2) as precursors. The In2O3 films can be deposited preferentially at relatively low temperatures of 160–200 °C, exhibiting a stable growth rate of 1.4–1.5 Å/cycle. The surface roughness of the deposited film increases gradually with deposition temperature, which is attributed to the enhanced crystallization of the film at a higher deposition temperature. As the deposition temperature increases from 150 to 200 °C, the optical band gap (Eg) of the deposited film rises from 3.42 to 3.75 eV. In addition, with the increase of deposition temperature, the atomic ratio of In to O in the as-deposited film gradually shifts towards that in the stoichiometric In2O3, and the carbon content also reduces by degrees. For 200 °C deposition temperature, the deposited film exhibits an In:O ratio of 1:1.36 and no carbon incorporation. Further, high-performance In2O3 thin-film transistors with an Al2O3 gate dielectric were achieved by post-annealing in air at 300 °C for appropriate time, demonstrating a field-effect mobility of 7.8 cm2/V⋅s, a subthreshold swing of 0.32 V/dec, and an on/off current ratio of 107. This was ascribed to passivation of oxygen vacancies in the device channel.

The energy band alignment of AlN/β-Ga₂O₃ heterostructures was investigated by X-ray photoelectron spectroscopy. The valence band offsets were estimated to be −0.09 ± 0.1 eV (type II alignment) for AlN grown by plasma enhanced atomic layer deposition (PEALD) on β-Ga₂O₃ and 0.72 ± 0.1 eV (type I alignment) for AlN prepared by thermal atomic layer deposition (T-ALD) on β-Ga₂O₃, which gives the conduction band offsets of 1.39 ± 0.1 eV for PEALD AlN and 0.58 ± 0.1 eV for T-ALD AlN. The large difference in the band alignment for the AlN/β-Ga₂O₃ heterostructures is dominated by different levels of oxygen incorporation into the AlN films as a result of different deposition techniques. The determination of the band alignment of the AlN/β-Ga₂O₃ heterostructure has significant implications for the design of electronic and optical devices based on AlN/β-Ga₂O₃ heterojunctions.

The MoS ₂ photodetector on different substrates stacked via van der Waals force has been explored extensively because of its great potential in optoelectronics. Here, we integrate multilayer MoS ₂ on monocrystalline SiC substrate though direct chemical vapor deposition. The MoS ₂ film on SiC substrate shows high quality and thermal stability, in which the full width at half‐maximum and first‐order temperature coefficient for the Raman mode are 4.6 cm ⁻¹ and −0.01382 cm ⁻¹ /K, respectively. The fabricated photodetector exhibits excellent performance in the UV and visible regions, including an extremely low dark current of ~1 nA at a bias of 20 V and a low noise equivalent of 10 ⁻¹³ –10 ⁻¹⁵ W/Hz ^1/2 . The maximum responsivity of the MoS ₂ /SiC photodetector is 5.7 A/W with the incident light power of 4.35 μW at 365 nm (UV light). Furthermore, the maximum photoconductive gain, noise equivalent power, and normalized detectivity for the fabricated detector under 365 nm illumination are 79.8, 7.08 × 10 ⁻¹⁵ W/Hz ^1/2 , and 3.07 × 10 ¹⁰ Jonesat, respectively. We thus demonstrate the possibility for integrating high‐performance photodetectors array based on MoS ₂ /SiC via direct chemical vapor growth.

In this work, we report high-performance amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs) with atomic layer deposited Al ₂ O ₃ dielectric processed at a minimal temperature of 189.6 °C via microwave annealing (MWA). The a-IGZO TFT with MWA exhibits an improvement of 57% in subthreshold swing (SS) compared with the unannealed device; meanwhile, it retains high field-effect mobility of up to 29.2 cm ² /(V $\cdot $ s) and large switching ratio of >10 ⁸ . Moreover, the SS of the device was further reduced through a two-step MWA treatment. It is believed that MWA treatment effectively reduces the density of trap states associated with oxygen vacancies, promotes the formation of lattice oxygen, and thus improves the quality of IGZO film. MWA with low thermal budget shows great potential in applications of the back-end of line (BEOL)-compatible oxide devices.

The energy band alignment of the atomic-layer-deposited In₂O₃/β-Ga₂O₃ ($\overline{2}01$ ) interface is evaluated by X-ray photoelectron spectroscopy. The X-ray diffraction pattern reveals that the In₂O₃ film grown at 160 °C is amorphous, while it becomes polycrystalline at a higher deposition temperature of 200 °C. The bandgaps, determined by reflection electron energy loss spectroscopy, are 4.65, 3.85, and 3.47 eV for β-Ga₂O₃, polycrystalline In₂O₃, and amorphous In₂O₃, respectively. Both amorphous and polycrystalline In₂O₃/β-Ga₂O₃ interfaces have Type I alignment. The conduction and valence band offsets at the polycrystalline (amorphous) In₂O₃/β-Ga₂O₃ interface are 0.35 and 0.45 eV (0.39 and 0.79 eV), respectively. These observations suggest that polycrystalline In₂O₃ as an intermediate semiconductor layer is beneficial to the barrier reduction of metal/Ga₂O₃ contact.