Two-inch Ga2O3 films with ( 201)-orientation are grown on 𝑐-sapphire at 850-1050 ∘ C by hydride vapor phase epitaxy. High-resolution x-ray diffraction shows that pure 𝛽-Ga2O3 with a smooth surface has a higher crystal quality, and the Raman spectra reveal a very small residual strain in 𝛽-Ga2O3 grown by hydride vapor phase epitaxy compared with bulk single crystal. The optical transmittance is higher than 80% in the visible and near-UV regions, and the optical bandgap energy is calculated to be 4.9 eV.

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In this work, we prepared the β -Ga 2 O 3 @GaN nanowires (NWs) by oxidizing GaN NWs. High-quality hexagonal wurtzite GaN NWs were achieved and the conversion from GaN to β -Ga 2 O 3 was confirmed by x-ray diffraction, Raman spectroscopy and transmission electron microscopy. The effect of the oxidation temperature and time on the oxidation degree of GaN NWs was investigated systematically. The oxidation rate of GaN NWs was estimated at different temperatures.

The GaN thick films have been grown on porous GaN template and planar metal-organic chemical vapor deposition (MOCVD)-GaN template by halide vapor phase epitaxy (HVPE). The analysis results indicated that the GaN films grown on porous and planar GaN templates under the same growth conditions have similar structural, optical, and electrical properties. But the porous GaN templates could significantly reduce the stress in the HVPE-GaN epilayer and enhance the photoluminescence (PL) intensity. The voids in the porous template were critical for the strain relaxation in the GaN films and the increase of the PL intensity. Thus, the porous GaN converted from β-Ga2O3 film as a novel promising template is suitable for the growth of stress-free GaN films.

Single-crystal GaN layers have been obtained by nitriding β-Ga2O3 films in NH3 atmosphere. The effect of the temperature and time on the nitridation and conversion of Ga2O3 films have been investigated. The nitridation process results in lots of holes in the surface of films. The higher nitridation temperature and longer time can promote the nitridation and improve the crystal quality of GaN films. The converted GaN porous films show the single-crystal structures and low-stress, which can be used as templates for the epitaxial growth of high-quality GaN.