High-frequency and below bandgap anisotropic dielectric constants in <i>?</i>-(Al_<i>x</i>Ga_1?<i>x</i>)₂O₃ ( 0?x?1)

A Mueller matrix spectroscopic ellipsometry approach was used to investigate the anisotropic dielectric constants of corundum ?-(AlxGa1?x)2O3 thin films in their below bandgap spectral regions. The sample set epitaxially grown using plasma-assisted molecular beam epitaxy on m-plane sapphire. measurements were performed at multiple azimuthal angles resolve uniaxial properties. Cauchy dispersion model applied, and high-frequency are determined for polarization perpendicular (??,?) parallel (??,?) film c-axis. optical birefringence is negative throughout composition range, overall index refraction substantially decreases upon incorporation Al. We find small bowing parameters with b?=0.386 b?=0.307.