Structural and Optical Properties of β-Ga2O3 Thin Films Grown by Plasma-Assisted Molecular Beam Epitaxy
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Epitaxial beta-gallium oxide (β-Ga2O3) has been deposited on c-plane sapphire by plasma-assisted molecular-beam epitaxy technique using two methods. One method relied on a compound Ga2O3 source with oxygen plasma while the second used elemental Ga source with oxygen plasma. A side-by-side comparison of the growth parameters between these two methods has been demonstrated. With various substrate temperatures, pure phase (¯201) oriented β-Ga2O3 thin films were obtained using both sources. Reflection high energy electron diffraction patterns displayed a threefold reconstruction during the growth. X-ray photoelectron spectroscopy analysis showed a shift in the binding energy of the Ga 2p peaks consistent with a Ga being in a +3 oxidation state. For transparent oxide like β-Ga2O3, it is important to determine the index of refraction (n) and its functional dependence on the wavelength. The Cauchy dispersion relation was employed to evaluate the refractive index, film thickness, roughness values, and extinction coefficient. The band gap energies of the thin films were calculated to be ~5.02 eV by extrapolating the linear portion of Tauc-plot analysis and the refractive index is ~1.89 at the wavelength (λ) of 6328 Å, suggesting high structural quality and packing density of the oxide films.