Metalorganic chemical vapor deposition of α-Ga2O3 and α-(AlxGa1-x)2O3 thin films on m-plane sapphire substrates

Single alpha-phase (AlxGa1-x)(2)O-3 thin films are grown on m-plane sapphire (alpha-Al2O3) substrates via metalorganic chemical vapor deposition. By systematically tuning the growth parameters including the precursor molar flow rates, chamber pressure, and growth temperature, the epitaxial growth of high-quality phase pure alpha-(AlxGa1-x)(2)O-3 films (0 <= x <= 1) is demonstrated with smooth surface morphologies and alloy homogeneities by comprehensive material characterization. The asymmetrical reciprocal space mapping reveals fully relaxed films for alpha-(AlxGa1-x)(2)O-3 films with x <= 0.5. The coherent growth of alpha-(AlxGa1-x)(2)O-3/alpha-Al2O3 superlattice structures is demonstrated with abrupt interfaces and uniform Al distribution for higher Al compositions at x = 0.78 in the alpha-(AlxGa1-x)2O3 layer. The influence of growth parameters, such as growth temperature and chamber pressure, on the phase stabilization and Al incorporation in the alpha-(AlxGa1-x)(2)O-3 films is investigated. While lower growth temperatures facilitate the phase stabilization of a-Ga2O3 thin films, lower chamber pressure leads to higher Al incorporation in alpha-(Al(x)Ga(1-)x)(2)O-3 films. High resolution x-ray photoelectron spectroscopy was utilized for determining the Al compositions and bandgaps of alpha-(AlxGa1-x)(2)O-3. Furthermore, the evolution of the valance and conduction band offsets at alpha-Al2O3/alpha-(AlxGa1-x)(2)O-3 heterojunctions is evaluated with the variation of Al compositions, which reveals the formation of type-I (straddling) band alignment between alpha-Al2O3 and alpha-(AlxGa1-x)(2)O-3. (C) 2021 Author(s).