Xueqiang Ji

Here, a bias-tunable dual-mode ultraviolet (UV) photodetector based on p-Mg-GaN/β-Ga2O3 heterojunction is reported. The device mainly responds to UVC (254 nm) under reverse bias and actively switches to UVA (365 nm) response under low forward bias. When the forward bias voltage exceeds ∼2 V, a significant negative photoconductivity (NPC) phenomenon occurs. Under 365 nm illumination, the NPC originates from the instantaneous filling of interface states and the barrier modulation at the heterojunction. In contrast, the mechanism under 254 nm illumination exhibits a strong bias dependence: at 4 V, it is governed by a slow process associated with bulk deep-level states; when the bias increases to 6 V, the dominant process changes to rapid interface barrier modulation. This study reveals the bias-tunable NPC mechanism switching phenomenon in Ga2O3 heterojunctions and provides a new physical basis and material platform for the design of intelligent ultraviolet photodetectors with spectral selectivity and adjustable polarity.

The ultra wide bandgap semiconductor gallium oxide (Ga₂O₃) has emerged as a promising platform for next-generation high-voltage power electronics due to its wide bandgap (~4.8 eV), high critical electric field (~8MV/cm), and favorable figures of merit. However, conventional Ga₂O₃ lateral metal–oxide–semiconductor field-effect transistors (MOSFETs) lack a body diode, resulting in a high reverse turn-on voltage and significant reverse conduction loss, which limits practical applications. In this work, we report the experimental realization of a Ga₂O₃ lateral MOSFET with an integrated freewheeling diode (IFD). The proposed structure enables low-voltage reverse conduction without compromising forward performance or breakdown characteristics. The IFD MOSFET demonstrates a marked reduction in reverse turn-on voltage (−0.89 V), representing a 90%–94% decrease compared with conventional devices. Forward transfer and output characteristics remain comparable. Breakdown measurements yield a voltage of 2.5 kV with a $\text{20}~\mu $ m drift region. These results demonstrate the feasibility of integrating freewheeling diodes in Ga₂O₃ MOSFETs, providing a practical pathway to low-loss and high-voltage power switching devices.

As an emerging ultra-wide bandgap semiconductor, gallium oxide (Ga2O3) has attracted considerable research interest since its discovery. It exhibits outstanding material properties and compatibility with low-cost fabrication techniques, making it a highly promising candidate for next-generation ultra-high power and high-frequency applications. Over the past decades, Ga2O3-based transistors have undergone rapid development and demonstrated strong potential in various domains. This review systematically summarizes recent progress in the architecture and performance of β-Ga2O3 transistors that have garnered significant attention. We approach this review from the perspective of application domains, and within each category, we further discuss device variations in detail based on structural configurations or operating mechanisms. Key structures covered include lateral and vertical β-Ga2O3 metal–oxide–semiconductor field-effect transistors for power electronics, radio frequency β-Ga2O3 transistors, and β-Ga2O3 thin-film transistors for flexible applications. This work aims to provide a comprehensive reference and to inspire future research directions in the field of Ga2O3 transistor technologies.

In this work, we systematically investigated the degradation and recovery behaviors of p-NiO/n-Ga₂O₃ heterojunction barrier Schottky diodes (HJBS) under high-temperature forward bias (HTFB) stress. Furthermore, based on the observed degradation trends in the device’s DC characteristics, a comprehensive analysis was conducted to elucidate the underlying degradation mechanisms. The as-fabricated HJBS structure, based on a p-NiO/n-Ga₂O₃ heterojunction, exhibited excellent electrical performance with a breakdown voltage exceeding 1kV and an on-resistance of 9.23 m $\Omega \cdot $ cm². However, during actual circuit operation, devices are inevitably subjected to high-temperature and high-current stress conditions, leading to significant degradation in turn-on voltage and on-resistance. These challenges impose stricter requirements on the reliability of HJBS devices. The device underwent forward bias stress followed by recovery evaluation. After the forward bias stress (2.5 V at $25~^{\circ }$ C) for 15ks, only a 5.2% degradation in the turn-on voltage increase ( $\Delta {V}_{\text {on}}$ ) was observed. This degradation is attributed to the electron capture associated with donor traps. During the subsequent recovery phase, a nonrecoverable degradation of 2.7% in $\Delta {V}_{\text {on}}$ was recorded, which is believed to be caused by the presence of defects compensation or passivation within the bulk material that impeded the release of trapped electrons. These findings provide important insights for improving the reliability of Ga₂O₃ power devices.

β-Ga2O3 is rapidly emerging as a leading material for next-generation high-power electronic devices due to its exceptional material properties, such as a high breakdown field and a superior Baliga's figure of merit. Vertical β-Ga2O3 Schottky barrier diodes (SBDs) offer advantages, including high on-current density and efficient chip area utilization; however, these benefits also result in elevated power density. Due to the low thermal conductivity of β-Ga2O3, the junction temperature during forward operation is potentially higher than that of SiC and GaN devices, which poses a greater challenge to its long-term reliability. A comprehensive understanding of the on-state reliability for the β-Ga2O3 SBDs is still lacking. Here, we address this gap by employing a measure–stress–measure approach to systematically investigate the real-time degradation and recovery behavior of key performance parameters—turn-on voltage (Von) and on-resistance (Ron)—in the β-Ga2O3 SBDs. We subject these devices to prolonged forward bias stress (5–9 V) and varying temperature conditions (25–125 °C) to assess their degradation characteristics and mechanisms. Notably, at an operating temperature of 125 °C, these β-Ga2O3 SBDs are projected to function reliably for almost a decade at an operating voltage of 1.46 V, assuming a 5% shift in Von as the failure criterion. This exceptional robustness, attributed to both the inherent material properties of β-Ga2O3 and the quality of the β-Ga2O3 Schottky interface, highlights the potential of β-Ga2O3 for long-term, high-performance applications in demanding power electronics.

High surface fields represent an inherent trade-off for Ga ₂ O ₃ power devices concerning their on-state energy consumption and voltage capability. This work proposes a Ga ₂ O ₃ Schottky barrier diode that incorporates an embedded trench Schottky junction and a metal-oxide-semiconductor (MOS) capacitor. This structure aims to reduce surface field and mitigate the peak electric field, thus achieving low power consumption and high breakdown voltage. Leveraging the trench design, the T-SBD achieves a breakdown voltage of 571 V, double that of a conventional SBD (285 V). The trench-wrapped electrodes enhance sidewall depletion under reverse bias, while the MOS capacitor grid columns further suppress leakage current to as low as 8.6 μA cm ⁻² . Furthermore, TCAD simulation results further demonstrate the effective electric field optimization of the devices with Trench SBD structure. This research lays a solid foundation for the development of higher-power Ga ₂ O ₃ Schottky diodes.

The Ga₂O₃-based memristors, fabricated via electron beam evaporation (EBE), exhibit both volatile and nonvolatile resistive switching behaviors. The nonvolatile Ga₂O₃-based memristors exhibit remarkable resistive switching properties, featuring outstanding cyclic stability, a substantial switching window (>100), and notably low SET/RESET voltages. The observed dual switching modes are attributed to filamentary conduction driven by metallic Cu filaments assisted by oxygen vacancies. The studied Ga₂O₃-based devices demonstrate both electrically and optically tunable synaptic functionalities, including paired-pulse facilitation (PPF), spike-rate-dependent plasticity (SRDP), spike-timing-dependent plasticity (STDP), potentiation and depression behaviors, as well as light-induced memory characteristics and learning-forgetting capabilities. Intriguingly, high recognition precision of 89.14% on Fashion-MNIST and 97.84% on modified National Institute of Standards and Technology database (MNIST) indicates that wide bandgap semiconductor Ga₂O₃-based memristors hold immense potential for advancing future neuromorphic computing.