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In this work, (Al x Ga 1-x) 2 O 3 thin films were grown on Al 2 O 3 (0001) substrate by radio frequency magnetron sputtering using Al/Ga 2 O 3 target. The analysis of crystalline structure, morphology, transmittance and bandgap after various annealing temperatures were investigated in detail. The films were oriented along ( 2 — 01) plane, and the crystalline quality improved with increasing annealing temperature. The stoichiometries of films can be regard as (Al 0.33 Ga 0.67) 2 O 3 according to X-ray photoelectron spectroscopy and the additional compressive stress in the sample which annealed at 900 °C was certified. The bandgap of annealed films was totally decreased due to increasing magnitude of compressive stress and grain size. Therefore, these results may suggest the way to tune the band gap of β-(Al x Ga 1-x) 2 O 3 films by varying the residual stress through annealing and indicate the optimum annealing temperature for (Al 0.33 Ga 0.67) 2 O 3 thin films is about 800 °C. • The (Al x Ga 1-x) 2 O 3 films were deposited using Al/Ga 2 O 3 target. • All the samples were monoclinic structure with the (−201) preferred orientation. • Post-annealing can improve the crystalline of (Al x Ga 1-x) 2 O 3 thin films. • The remigration of Al atoms took place after annealing at 900 °C. [ABSTRACT FROM AUTHOR]

The (In x Ga 1-x) 2 O 3 thin films were deposited on sapphire substrates by radio frequency magnetron sputtering with increasing sputtering pressure from 0.6 Pa to 1.6 Pa. X-ray diffraction analysis indicated In composition of (In x Ga 1-x) 2 O 3 thin films maintained constant with the increase of sputtering pressure and In content and bandgaps of (In x Ga 1-x) 2 O 3 thin films were estimated to be 6% and 4.78 eV by Vegard's law, respectively. The influence of sputtering pressure on structural and optical properties was discussed in detail. Especially, the origin of different emission of (In x Ga 1-x) 2 O 3 thin films was investigated. The role of V Ga defects on the green emission centered at about 550 nm had been clarified. The energy band diagram of (In x Ga 1-x) 2 O 3 thin film was also proposed with intrinsic defect levels. • In content of (In x Ga 1-x) 2 O 3 films is 6% for all sputtering pressure condition. • Defects play an important role in luminescence. • Green luminescence is related to gallium vacancies. [ABSTRACT FROM AUTHOR]