【Member Papers】Long Hao’s Group at Xiamen University Achieves a Series of Advances in Ga₂O₃ Interface Control, Characterization, and Optoelectronic Devices Research

      The ultra-wide band gap semiconductor Ga₂O₃, owing to its excellent material properties, shows great potential for solar-blind ultraviolet detectors and high-power electronic devices. Interface control is a prerequisite for the stable operation of high-performance Ga₂O₃ optoelectronic devices. Recently, the research group led by Associate Professor Long Hao at Xiamen University has achieved a series of advances in the interface control of Ga₂O₃ optoelectronic devices, providing insights for further understanding the Ga₂O₃ interface mechanism.

Ga₂O₃-Based MOS Capacitor Interface Control and High-Performance Schottky Diodes

      The MOS capacitor structure is the core part of the gate control in MOSFET devices. Interfacial defects strongly affect characteristics such as the threshold voltage of the MOSFET. The research group characterized the interfacial defect （D_it）, boundary defect and bulk defect in Al₂O₃/Ga₂O₃ based MOS capacitors at high and low temperatures respectively through three test methods: high/low frequency C-V, hysteresis C-V and forward stress C-V. The defect density at the Al₂O₃/Ga₂O₃ interface was reduced by 80% by means of oxygen plasma treatment and high-temperature oxygen annealing, thereby enhancing the stability of the MOS structure's threshold voltage. Based on the above interface state research, the research group further studied the formation of TiO₂ insertion layers by thermal oxidation of Ti metal and achieved high-performance Ga₂O₃ base Schottky diodes. Compared with traditional SBD, the PFOM of this device has increased by 16 times.

Figure 1: (a-d) Interface states and leakage current study of Al₂O₃/Ga₂O₃ based MOS capacitors; (e-f) Performance improvement of Ga₂O₃-based SBD based on interface state regulation.

Research on Interface States in Ga₂O₃-Based Photodetectors and High-Performance Devices

      In Ga₂O₃-based photodetectors, the existence of interface states has a significant impact on carrier transport, but the behavior of interface defect in light-dark states and during light-dark switching has not been systematically studied. The group characterized the interface properties of MSM photodetectors based on Ga₂O₃ using frequency-variable C–V measurements at different temperatures. It was found that the interface state density in MSM photodetectors increased with temperature and bias voltage, while the carrier capture time decreased with temperature. In the dark, the current of MSM photodetectors is dominated by the Poole–Frenkel (PF) tunneling mechanism, whereas under illumination, photogenerated carriers mainly follow the thermionic emission (TE) mode. The detector’s response time is limited by the carrier trapping and filling processes at interface defects. Building on these interface state studies, the group has recently collaborated with the research teams of Professor Zhang Hongliang and Professor Yang Weifeng at Xiamen University to investigate MSM photodetectors incorporating Fabry–Perot (FP) microcavities and p-(Al)GaN/n-Ga₂O₃ PN-junction detectors. The half-peak width of the responsivity curve for FP-microcavity MSM photodetectors was only 18.4 nm. The heterojunction PN detector based on p-(Al)GaN/n-Ga₂O₃ achieved selectivity ratios of 1.47×10⁵ for UVC/UVB (R₂₄₇nm / R₃₀₀nm) and 3.71×10⁵ for UVC/UVA (R_247nm /R_300nm) at zero bias, with a single-exponential response time of only 31 μs.

Figure 2:(a) Influence of interface states on the current conduction mechanism in MSM-PDs;(b) Ultrafast Ga₂O₃-based PN-junction photodetector;(c) High-selectivity-ratio Ga₂O₃ PN-junction photodetector;(d) Comparison of key indicators of Ga₂O₃-based heterojunction PDs in the research group.

Research Support

      This research was supported by the National Natural Science Foundation of China (62174140).

References

      (1) Cai, Z.; He, X.; Wang, K.; Hou, X.; Mei, Y.; Ying, L.; Zhang, B.; Long, H. Enhancing Performance of GaN/Ga₂O₃ P‐N Junction Uvc Photodetectors via Interdigitated Structure. Small Methods 2023, 8 (7), 2301148.

      (2) Chen, S.; Du, S.; Wang, K.; Qiao, L.; Zhang, C.; Yang, W.; Li, Q.; Zheng, Z.; Mei, Y.; Long, H. Improved β-Ga₂O₃ Schottky Barrier Diodes via Thermal Oxidation of Titanium Insertion Layer. Micro and Nanostructures 2024, 190, 207831.

      (3) He, X.; Sun, R.; Xu, X.; Geng, H.; Qi, S.; Zhang, K. H.; Long, H. Excellent Wavelength Selectivity of P-AlGaN/n-Ga₂O₃ Solar-Blind UVC PD. ACS Appl. Mater. Interfaces 2024, 16 (46), 64146–64155.

      (4) Du, S.; Lin, Y.; Xu, H.; Long, H. Investigation of Interface, Border and Bulk Traps of Al₂O₃/β-G₂O₃ MOS Capacitors via O₂ Plasma Treatment. Micro and Nanostructures 2025, 198, 208058.

      (5) Sun, R.; Xu, H.; He, X.; Xu, X.; Du, S.; Zhang, K. H.; Long, H. Current Mechanism and Interface States in Ga₂O₃ MSM Solar-Blind Photodetector. Surfaces and Interfaces 2025, 72, 106949.

      (6) Lin, Y.; Du, S.; Long, H. Effect of Oxygen in the Annealing Treatment of Al₂O₃/β-Ga₂O₃ MOS Capacitors. Micro and Nanostructures 2025, 208, 208321.

      (7)Taoan Wang, Xiyao He, Hao Xu, Ruoting Sun, Xiangyu Xu, Kelvin Hongliang Zhang, Hao Long. Enhanced Performance of Ga₂O₃-based MSM-PD by Fabry-Pérot microcavity. Optics Letters (accepted)