Structural and electrical properties of thick κ-Ga₂O₃ grown on GaN/sapphire templates

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 E_c − 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.