Effect of Annealing on Al Diffusion and its Impact on the Properties of Ga ₂ O ₃ Thin Films Deposited on c‐Plane Sapphire by RF Sputtering

Gallium oxide is a wide‐bandgap semiconductor which has been steadily growing in popularity due to its ultrawide bandgap, suitability for harsh environments, and distinctive optoelectrical properties. Notable applications include deep‐UV photodetectors, low‐loss waveguides, or even transparent solar cells. RF sputtering stands out among possible techniques for the deposition of thin films with high quality and at a low cost. By using sapphire substrates, and through thermal annealing, a alloy can be formed by Al diffusion, which has tunable optoelectrical properties such as the bandgap and breakdown electric field. In this work, techniques such as X‐Ray diffraction, Rutherford backscattering spectrometry, Raman spectroscopy, atomic force microscopy, and optical transmission are used to determine the optical properties, morphology, and the composition of the deposited and annealed thin films. To explore the formation of the alloy, annealing is performed at variable temperature, in ambient air. It is determined that the bandgap can indeed be tuned between 4.85 and 5.30 eV by varying the annealing temperature, corresponding to an Al molar fraction x between 0 and 43.8%.