Browsing by Author "Xu, Mingfei"

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    A review of ultrawide bandgap materials: properties, synthesis and devices
    (Oxford University Press, 2022) Xu, Mingfei; Wang, Dawei; Fu, Kai; Mudiyanselage, Dinusha Herath; Fu, Houqiang; Zhao, Yuji
    Ultrawide bandgap (UWBG) materials such as diamond, Ga2O3, hexagonal boron nitride (h-BN) and AlN, are a new class of semiconductors that possess a wide range of attractive properties, including very large bandgap, high critical electric field, high carrier mobility and chemical inertness. Due to these outstanding characteristics, UWBG materials are promising candidates to enable high-performance devices for power electronics, ultraviolet photonics, quantum sensing and quantum computing applications. Despite their great potential, the research of UWBG semiconductors is still at a nascent stage and represents a challenging interdisciplinary research area of physics, materials science and devices engineering. In this review, the material properties, synthesis methods and device applications of UWBG semiconductors diamond, Ga2O3, h-BN and AlN will be presented and their recent progress, challenges and research opportunities will be discussed.
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    Characterizations of two-photon absorption process induced by defects in aluminum nitride using Z-scan method
    (IOP Publishing, 2024) Zhou, Jingan; Li, Tao; Zhao, Xuan; Zhang, Xiang; Doumani, Jacques; Xu, Mingfei; He, Ziyi; Luo, Shisong; Mei, Zhaobo; Chang, Cheng; Robinson, Jacob T.; Ajayan, Pulickel M.; Kono, Junichiro; Zhao, Yuji; Smalley-Curl Institute
    In this work, we reported two-photon absorption (TPA) measurements for aluminum vacancies in Aluminum nitride single crystals. We measured the linear transmission and identified the defect levels. Using the Z-scan method, we measured the TPA coefficients of the transitions between defect levels from 380 nm to 735 nm. The transition occurs between the aluminum vacancies defect levels. Furthermore, the power dependence shows good linear fitting, confirming the TPA mechanism. These results will be helpful for the design and fabrication of ultra-low loss waveguides and integrated photonics in the ultraviolet spectral range.
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    Power Electronics Based on Ultrawide Bandgap Semiconductors: from Material Engineering to Device Applications
    (2023-11-16) Xu, Mingfei; Zhao, Yuji
    This work demonstrates high-performance BN/β-Ga2O3 metal-insulator-semiconductor Schottky barrier diodes (MIS SBDs). The BN layer is directly grown on the β-Ga2O3 by pulsed laser deposition (PLD). The presence of a ~2.8 nm BN layer is confirmed by a series of techniques, including X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and high-resolution transmission electron microscopy (HRTEM). The MIS SBDs show an on/off ratio of ~ 107 and an increased on-resistance due to the insertion of the BN layer. An increased Schottky barrier height is observed from capacitance-voltage (C-V) measurements. Temperature-dependent measurements suggest the existence of an inhomogeneous Schottky barrier. The breakdown voltage is enhanced from 732 V for a regular SBD to 1045 V for a MIS SBD with the ultrathin BN layer, which can be ascribed to the increased Schottky barrier height and reduced leakage currents. This work provides a promising way to optimize the performance of β-Ga2O3-based devices for power electronics.