Redshift and amplitude increase in the dielectric function of corundum-like α-(TixGa1−x)2O3

Abstract

Redshift of the absorption onset and amplitude increase in the ultraviolet complex dielectric function (DF) of corundum-like α-(TixGa1−x)2O3 with increasing Ti content is presented. α-Ga2O3 thin film samples alloyed with Ti up to x=0.61 are grown from plasma enhanced atomic layer deposition. They are characterized by ultraviolet spectroscopic ellipsometry, transmission electron microscopy, and x-ray photoelectron spectroscopy (XPS). The samples are shown to be crystalline up to x=0.053. Ellipsometry is employed to obtain the ordinary complex DF, where the absorption onset shows a strong red shift with increasing Ti content as well as an increase in amplitude, which is associated with a successive take over of Ti related 3d-states in the density-of-states. Valence band XPS results lead to the conclusion that the strong red shift in the absorption onset with increasing Ti content is mainly due to conduction band lowering and less from the valence band.