Epitaxial growth of γ-(AlxGa1-x)O3 alloy films for band-gap engineering

Defective-spinel-structured gamma-(AlxGa1-x)(2)O-3 alloy films were successfully stabilized on MgAl2O4 substrates for the entire composition range using molecular beam epitaxy, though both end members are metastable. The crystallinity of the alloy films (x >= 0.22) was considerably better than that of the gamma-Ga2O3 film, indicating that the Al2O3 lattice is more flexible and sensitive to the epitaxial force exerted by the substrate than Ga2O3 lattice. The direct and indirect band gaps obtained using deep-UV spectroscopy were in the ranges of 4.96-6.97 and 4.80-6.86 eV, for which the bowing parameters were 0.183 and 0.43 eV, respectively. Our results will be beneficial for further development of gamma-(AlxGa1-x)(2)O-3 systems. (C) 2017 The Japan Society of Applied Physics