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Films of α-Ga 2 O 3 grown by Halide Vapor Phase Epitaxy (HVPE) were irradiated with protons at energies of 330, 400, and 460 keV with fluences 6 × 10 15  cm −2 and with 7 MeV C 4+ ions with a fluence of 1.3 × 10 13  cm −2 and characterized by a suite of measurements, including Photoinduced Transient Current Spectroscopy (PICTS), Thermally Stimulated Current (TSC), Microcathodoluminescence (MCL), Capacitance–frequency (C–f), photocapacitance and Admittance Spectroscopy (AS), as well as by Positron Annihilation Spectroscopy (PAS). Proton irradiation creates a conducting layer near the peak of the ion distribution and vacancy defects distribution and introduces deep traps at E c -0.25, 0.8, and 1.4 eV associated with Ga interstitials, gallium–oxygen divacancies V Ga –V O , and oxygen vacancies V O . Similar defects were observed in C implanted samples. The PAS results can also be interpreted by assuming that the observed changes are due to the introduction of V Ga and V Ga –V O . 

A review is given of reported trap states in the bandgaps of different polymorphs of the emerging ultrawide bandgap semiconductor Ga₂O₃. The commonly observed defect levels span the entire bandgap range in the three stable (β) or meta-stable polymorphs (α and ɛ) and are assigned either to impurities such as Fe or to native defects and their complexes. In the latter case, the defects can occur during crystal growth or by exposure to radiation. Such crystalline defects can adversely affect material properties critical to device operation of transistors and photodetectors, including gain, optical output, threshold voltage by reducing carrier mobility, and effective carrier concentration. The trapping effects lead to degraded device operating speed and are characterized by long recovery transients. There is still significant work to be done to correlate experimental results based on deep level transient spectroscopy and related optical spectroscopy techniques to density functional theory and the dominant impurities present in the various synthesis methods to understand the microscopic nature of defects in Ga₂O₃.