β-(AlxGa1-x)2O3/Ga2O3 (010) heterostructures grown on β-Ga2O3 (010) substrates by plasma-assisted molecular beam epitaxy

By systematically changing growth parameters, the growth of beta-(AlxGa1-x)(2)O-3/Ga2O3 (010) heterostructures by plasma-assisted molecular beam epitaxy was optimized. Through variation of the Al flux under O-rich conditions at 600 degrees C, beta-(AlxGa1-x)(2)O-3 (010) layers spanning similar to 10% to similar to 18% Al2O3 were grown directly on beta-Ga2O3 (010) substrates. Nominal beta-(AlxGa1-x)(2)O-3 (010) compositions were determined through Al:Ga flux ratios. With x = similar to 0.18, the beta-(AlxGa1-x)(2)O-3 (020) layer peak in a high-resolution x-ray diffraction (HRXRD) x-2h scan was barely discernible, and Pendellosung fringes were not visible. This indicated that the phase stability limit of Al2O3 in beta-Ga2O3 (010) at 600 degrees C was less than similar to 18%. The substrate temperature was then varied for a series of beta-(Al similar to 0.15Ga similar to 0.85)(2)O-3 (010) layers, and the smoothest layer was grown at 650 degrees C. The phase stability limit of Al2O3 in beta-Ga2O3 (010) appeared to increase with growth temperature, as the beta-(AlxGa1-x)(2)O-3 (020) layer peak with x = similar to 0.18 was easily distinguishable by HRXRD in a sample grown at 650 degrees C. Cross-sectional transmission electron microscopy (TEM) indicated that beta-(Al similar to 0.15Ga similar to 0.85)(2)O-3 (010) layers (14.4% Al2O3 by energy dispersive x-ray spectroscopy) grown at 650 degrees C were homogeneous. beta-(Al similar to 0.20Ga similar to 0.80)(2)O-3 (010) layers, however, displayed a phase transition. TEM images of a beta-(Al similar to 0.15Ga similar to 0.85)(2)O-3/Ga2O3 (010) superlattice grown at 650 degrees C showed abrupt layer interfaces and high alloy homogeneity. (C) 2015 American Vacuum Society.