Variation of Band Gap and Lattice Parameters of beta -(Al sub(x)Ga sub(1-x)) sub(2) O sub(3) Powder Produced by Solution Combustion Synthesis

Single-phase monoclinic aluminum-gallium oxide powders, beta -(Al sub(x)Ga sub(1-x)) sub(2) O sub(3), have been produced by solution combustion synthesis for Al fraction 0 less than or equal to x < 0.8. alpha -(Al sub(x)Ga sub(1-x)) sub(2)O sub(3) is observed for x = 1, with mixed alpha + beta for x = 0.8. The contraction in lattice parameters and increase in band gap with increasing Al concentration were characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), respectively, and are compared with a first-principles density-functional theory calculation. A novel filtering procedure is described to reduce the uncertainty involved in measuring band gap using photoemission, and to remove asymmetry in XPS line shapes caused by differential charging of loose powder. The lattice parameters vary linearly with Al fraction, but exhibit a change in slope at x = 0.5 that is attributed to the difference between aluminum occupying tetrahedral and octahedral sites in the monoclinic lattice. The band gap changes linearly with local stoichiometry, including increasing when aluminum content at the surface is enriched relative to the interior, with a range of over 1.8 eV.