Search

Beta-gallium oxide ( $\beta $ -Ga2O3) has emerged as a promising semiconductor material for high-voltage, high-temperature, and radiation-resistant electronics, offering performance advantages that surpass those of silicon and other wide bandgap semiconductors. Breakthroughs in the fabrication process and structure designing have led to the rapid development of vertical $\beta $ -Ga2O3 power transistors and shown their potential superiority for next-generation power devices. In this article, we present a review of major types of vertical $\beta $ -Ga2O3 transistors including current aperture vertical electron transistors (CAVETs), vertical fin-channel field-effect transistors (FinFETs), vertical diffused barrier field-effect transistors (VDBFETs), and U-shaped trench-gate metal-oxide-semiconductor field-effect transistors (UMOSFETs). We present their operation principles, performance achievements, design evolutions, and detailed optimizations with mechanism research. Comparisons are highlighted to analyze the advantages and inadequacies caused by their unique process approaches and enhancement-mode realizations. In the end, we address challenges and outlooks for the future development of vertical $\beta $ -Ga2O3 transistors.

We proposed an electrothermal aging (ETA) technology to improve stability of threshold voltage ( ${V} _{\text {TH}}$ ) in fabricated NiO/ $\beta $ -Ga2O3 heterojunction-gate FET (HJ-FET). Firstly, the HJ-FET is treated by ETA with a gate stress ( ${V} _{\text {G},\text {Str}}$ ) of −8 V and a thermal stress rising to 60 °C. An interface dipole ionization model is proposed to explain the ETA mechanism. The two kinds of interface dipoles are permanently ionized under electrothermal stress, leading to a thinned space charge region (SCR) as well as the reduced recombination centers concentrations at heterojunction (HJ) interface, which is responsible for the negative and positive shift of the ${I}$ – ${V}$ curves for the HJ-FET and HJ-diode under gate negatively biased, respectively. Secondly, the device treated by ETA is placed for 100 days without stresses at room temperature (ETA + 100D), the forward electrical properties of the devices remain almost unchanged with the gate stress time, and fully consistent with the performance of the device with just completed ETA treatment, proving the credibility of the ETA method to improve stability. Thirdly, the reliability of the device was assessed by negative bias temperature instability (NBTI) and was found to be greatly enhanced. Significantly, at 40 °C, the shift ratio of ${V} _{\text {TH}}$ decreases greatly to 0.4% after ETA + 100D from 31% before ETA. Furthermore, the device exhibits high stability with an extremely low ${V} _{\text {TH}}$ shift ratio of 2.4% even up to 200 °C. Our work demonstrates the great potential of $\beta $ -Ga2O3 HJ devices after ETA for a stable operation in extreme environments.

In this work, a $\beta $ -Ga2O3 field-effect rectifier (FER) with a p-NiOx gate aimed at low conduction loss, low leakage current, and capability of on-chip integration has been demonstrated. The proposed FER exhibits a low turn-on voltage ( ${V}_{\text {on}}{)}$ of 0.85 V comparable to Schottky barrier diodes (SBDs). The p-NiOx in FER offers an additional conduction path at high forward bias, which enhances the forward current. Compared with the lateral heterojunction diode (HJD) and SBD on the same substrate, the FER shows the best tradeoff between ON-state and OFF-state power dissipation, including lower ${V}_{\text {on}}$ than HJD (~41% of HJD) and lower leakage current than SBD (four orders of magnitude lower). The merits of this structure also extend to the high-temperature operation regime of the device. Good rectification characteristics of FER are observed at elevated temperatures. The proposed FER with low ${V}_{\text {on}}$ , high-voltage blocking capability and process compatibility with field-effect transistors (FETs) has the potential of being used as a low-power loss rectifier in future $\beta $ -Ga2O3 power integrated circuits (ICs).

In this work, we demonstrate a novel conductivity-controlled junction termination extension (JTE) technique using p-type NiO—a key element for the potential commercialization of Ga2O3 power devices. The surface electric field at the Schottky edge is effectively suppressed by the p-type NiO JTE. Simultaneously, it can control the concentration of p-type NiO to maximize the breakdown voltage ( ${V}_{\text {br}}$ ) by changing the gas atmosphere during magnetron sputtering growth. The electrical characteristics of the $\beta $ -Ga2O3 Schottky barrier diodes (SBDs) with p-type NiO JTE are studied systematically. All $\beta $ -Ga2O3 SBDs with JTE show great advantages in terms of device performance parameters whether at room temperature or high temperature, which indicates the effectiveness of p-NiO JTE in reducing the fringe electric field. In particular, the $\beta $ -Ga2O3 SBDs with an optimized hole concentration of approximately $10^{{17}}$ cm $^{-{3}}$ for NiO in the JTE region exhibit a low specific ON-resistance of 2.9 $\text{m}\Omega $ cm2 and a high ${V}_{\text {br}}$ of 2.11 kV, yielding a high power figure-of-merit (PFOM) of 1.54 GW/cm2. Our results demonstrate the great potential of p-NiO as a controllable and reliable technique for junction engineering in $\beta $ -Ga2O3 power devices.

Superior performance $\beta $ -gallium oxide ( $\beta $ -Ga2O3) junction barrier Schottky (JBS) diode with a forward conduction current of 5.1 A (@2 V) and reverse breakdown voltage of 1060 V with an area of ${3} \times {3}$ mm2 is presented. Meanwhile, the high power figure of merit (PFOM) of 0.72 GW/cm2 is attributed to the implementation of the pn heterojunction and beveled field plate for a ${0}.{1} \times {0}.{1}$ mm2 diode. The switching characteristics of large-size $\beta $ -Ga2O3 JBS after encapsulation reveal a short reverse recovery time of 26.8 ns under switching conditions of di / dt up to 400 A/ $\mu \text{s}$ . In addition, a hybrid half-wave (HW) Cockcroft–Walton (CW) voltage multiplier is built first together with commercial SiC SBD, and the results show the competitive characteristics of $\beta $ -Ga2O3 JBS for SiC SBD, such as the almost same multiplication factor up to 3.81 in four-stage hybrid voltage multipliers compared with an all-SiC SBD-based circuit. The circuit efficiency is approximately 86.07% for $\beta $ -Ga2O3 diode-based hybrid voltage multipliers. These results demonstrate the enormous application potential of $\beta $ -Ga2O3 JBS significantly.

β-Ga2O3power diodes were expected to possess low turn-on voltage (Von), low reverse leakage (JR), and high blocking capability for low power losses. In this work, a low Von(0.48 V) β-Ga2O3heterojunction barrier Schottky diode (HJBS) with tungsten Schottky contact was achieved. Benefitting from the lateral depletion of p+-NiO to suppress JRoriginating from the low Schottky barrier, the blocking capability of β-Ga2O3HJBS was enhanced. The spacing width of p+-NiO was systematically studied to reveal its modulation effect on forward and reverse characteristics. This work provides a promising strategy for improving rectifier efficiency of β-Ga2O3diodes.

β-Ga2O3Schottky barrier diodes (SBDs) with low-defect epitaxial surface and effective termination are essential for realizing excellent blocking characteristics. This work systematically studied oxygen annealing at various temperatures, optimizing the epitaxial surface by reducing the surface roughness and dislocation density. Combined with mesa termination, the results showed that the breakdown voltage (Vbr) significantly increased from 845 V to 1532 V. The device with a 3 × 3 mm2anode size was fabricated simultaneously, and the high forward currents of 8.7 A@2 V and Vbr> 700 V were achieved. This work shows a possible solution for the commercialization of β-Ga2O3SBDs.