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In this article, the origin of severe drain–source current kink effect in $\beta $ -Ga2O3 MOSFETs has been exploited by means of temperature- and pulse-dependent current–voltage (I–V) analysis. By reducing the pulse biasing widths, whereby the self-heating effect was negligible, the output characteristics were free of kink but with a rather low drain–source current density ( ${I}_{\text {DS}}$ ) at a high drain voltage ( ${V}_{\text {DS}}$ ) of 30 V. The current kink effect started to occur with a direct-current power consumption of approximately 850 mW/mm. The elimination of kink features was also observed together with a large ${I}_{\text {DS}}$ at elevated temperatures over 100 °C. These observations indicate that the kink effect is strongly related to thermal activation of incomplete ionized donors by either the self-heating effect or external intentional heating stress rather than high electric field. In terms of temperature-dependent current output characteristics, the thermal activation energy is determined to be 136 meV, which is consistent with the reported unintentional donors with a high activation energy of 110 meV. It implies that additional electrons are thermally activated and emitted from the incomplete ionized donors in $\beta $ -Ga2O3 channel or buffer layers through the self-heating effect, contributing to the channel conductivity modulation and the consequent current kink effect. These findings may bridge the knowledge gap between charge transport mechanisms and the reliability degradation of $\beta $ -Ga2O3 power switches.

In this article, the current collapse (CC) and current enhancement (CE) of the hydrogen-terminated diamond (H-diamond) MOSFET are found. The nonmonotonic variation of the drain current (DC) due to the long-term trapping effects is characterized by a proposed method, which involves the transient current measurements and the energy-level extractions. Based on the method, the measured transient current is utilized to infer that the abnormal phenomena are caused by the combined effect of the trapping near the gate and the absorption of atmospheric components on the surface of the device. With the extracted energy levels, the CC is deduced to be induced by the surface trap. The energy diagram for the surface trap in the H-diamond is given to make the trapping mechanism more clearly. By changing the test atmosphere, the CE is found to be caused by the component of the air. This work is useful for improving the performance of the H-diamond device.

Diamond-based devices with high ON/ OFF ratio are promising candidates for power and sensor applications. However, the limited ON/ OFF ratio caused by relatively high leakage currents still remains to be a problem. Herein, we present hydrogen-terminated diamond metal–insulator–semiconductor field-effect transistors (MISFETs) with a 40-/100-nm aluminum oxide/hafnium dioxide stacked passivation layer to reduce leakage currents. Due to the stacked passivation layer, the fringing capacitances were introduced and the electric field at the drain edge of the gate was reduced. Encouragingly, the drain and gate leakage currents were reduced to the order of $10^{-{9}}$ mA/mm under OFF-state conditions at room temperature. Consequently, an ON/ OFF ratio of $\sim 1\times 10^{{11}}$ was achieved, which is the highest value among the previously reported diamond-based field-effect transistors (FETs). Moreover, a record ON/ OFF ratio of $\sim 5\times 10^{{9}}$ was obtained even at 200 °C. Results of this work can pave the way for diamond-based devices in power or sensor applications.

Heterointegrated Ga2O3-on-SiC radio-frequency (RF) MOSFETs with record-high frequency performances were reported. A two-dimensional electron gas like channel with a high electron concentration and decent mobility was formed through the shallow implantation of Si into the $\beta $ -Ga2O3 (−201) nanomembrane integrated on the highly thermal conductive 4H-SiC substrate through an ion-cutting process. The resultant MOSFET yields a high current density of 661 mA/mm and a transconductance ( ${g}_{\text {m}}{)}$ of 57 mS/mm. A record-high current cut-off frequency ( ${f}_{\text {T}}{)}$ of 47 GHz and maximum oscillation frequency ( ${f}_{\text {max}}{)}$ of 51 GHz were achieved with the gate length ( ${L}_{\text {G}}{)}$ scaled down to $0.1~\mu \text{m}$ . Furthermore, the device with ${L}_{\text {G}}= 0.1\,\,\mu \text{m}$ showcases an output power density of 296 mW/mm and a high power gain of 11 dB at 2 GHz in continue wave (CW) mode. It is attributed to the enhanced gate control, elevated current output, and improved thermal conductivity of the heterointegrated Ga2O3 on SiC by ion-cutting process.

We report radio-frequency (RF) MOSFETs with a two-dimensional-electron-gas-like (2DEG-like) channel formed at the $\beta $ -Ga2O3 surface through the low-energy implantation of Si and rapid thermal activation process. The shallowly implanted channel exhibits a strong electron confinement near surface with a high sheet concentration of ${3}.{2}\times {10} ^{{13}}$ cm−3. With the high scaling of gate length ( ${L}_{\text {G}}{)}$ , the current cut-off frequency ( ${f}_{\text {T}}{)}$ and maximum oscillation frequency ( ${f}_{\text {max}}{)}$ were inversely proportional to ${L}_{\text {G}}$ along with a high electron saturation velocity of ${2}.{7}\times {10} ^{{6}}$ cm/s. The device with a ${L}_{\text {G}}$ of $0.15 ~\mu \text{m}$ demonstrates a high ${f}_{\text {T}}$ of 29 GHz and ${f}_{\text {max}}$ of 35 GHz, whilst preserving the high-voltage operation capability with a drain-to-source breakdown voltage ( $BV_{\text {DS}}{)}$ of 193 V. RF performance was verified by the power amplifying capability with a maximum power gain of 7 dB at 2 GHz for the device with ${L}_{\text {G}}$ of $0.5~\mu \text{m}$ .