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Thick (23 µm) films of κ-Ga2O3 were grown by Halide Vapor Phase Epitaxy (HVPE) on GaN/sapphire templates at 630 °C. X-ray analysis confirmed the formation of single-phase κ-Ga2O3 with half-widths of the high-resolution x-ray diffraction (004), (006), and (008) symmetric reflections of 4.5 arc min and asymmetric (027) reflection of 14 arc min. Orthorhombic κ-Ga2O3 polymorph formation was confirmed from analysis of the Kikuchi diffraction pattern in electron backscattering diffraction. Secondary electron imaging indicated a reasonably flat surface morphology with a few (area density ∼103 cm−2) approximately circular (diameter ∼50–100 µm) uncoalesced regions, containing κ-Ga2O3 columns with in-plane dimensions and a height of about 10 µm. Micro-cathodoluminescence (MCL) spectra showed a wide 2–3.5 eV band that could be deconvoluted into narrower bands peaked at 2.59, 2.66, 2.86, and 3.12 eV. Ni Schottky diodes prepared on the films showed good rectification but a high series resistance. The films had a thin near-surface region dominated by Ec − 0.7 eV deep centers and a deeper region (∼2 µm from the surface) dominated by shallow donors with concentrations of ≤1016 cm−3. Photocurrent and photocapacitance spectra showed the presence of deep compensating acceptors with optical ionization energies of ∼1.35 and 2.3 eV, the latter being close to the energy of one of the MCL bands. Deep level transient spectroscopy revealed deep traps with energies near 0.3, 0.6, 0.7, 0.8, and 1 eV from the conduction band edge. The results show the potential of HVPE to grow very thick κ-Ga2O3 on GaN/sapphire templates. 

The photocurrent produced by 259 nm wavelength excitation was measured in β-Ga2O3 Schottky diodes before and after neutron irradiation. These samples differed by the density of deep acceptors in the lower half of the bandgap as detected by capacitance–voltage profiling under monochromatic illumination. Irradiation led to a very strong increase in photocurrent, which closely correlated with the increase in deep trap density and the decrease after illumination of the effective Schottky barrier height due to hole capture by acceptors. A similar effect was observed on an as-grown βs-Ga2O3 film with a high density of deep acceptors. Electron beam induced current measurements indicated a strong amplification of photocurrent, which is attributed to the Schottky barrier lowering by holes trapped on acceptors near the surface. Photocurrent build-up and decay curves show several time constants ranging from several milliseconds to many seconds. These characteristic times are attributed to tunneling of electrons into the hole-filled acceptors near the surface and to thermal emission of holes from deep acceptors.