High-quality β-(AlxGa1-x)2O3 thin films on sapphire substrates by face-to-face annealing

High-quality beta-(AlxGa1-x)(2)O-3 thin films are fabricated through face-to-face annealing on sapphire substrates covered with epitaxial Ga2O3. Al atoms during high-temperature annealing are uniformly diffused from the sapphire substrate into the overlying Ga2O3 for (AlxGa1-x)(2)O-3 formation. The transformation of the (-201) crystal facet into the (300) crystal facet is observed, which is likely due to the lowest E-surf((hkl)) of the (100) surface. The crystallinity can be further improved with increasing the annealing temperatures and the duration of the thermal treatment under a tolerance limit of 1400 degrees C, which also increases the Al content to 0.68 in beta-(AlxGa1-x)(2)O-3 with a bandgap of up to 6.0 eV. As a result, highly-crystalline (300)-plane beta-(AlxGa1-x)(2)O-3 is obtained with a low X-ray diffraction (XRD) full width at half maximum (FWHM) at around 0.08 degrees (288 arcsec). These findings contribute to the understanding of the preparation of high-quality beta-(AlxGa1-x)(2)O-3 films on sapphire substrates.