Elevated temperature spectroscopic ellipsometry analysis of the dielectric function, exciton, band-to-band transition, and high-frequency dielectric constant properties for single-crystal ZnGa2O4

We report the elevated temperature (22 degrees C <= T <= 600 degrees C) dielectric function properties of melt grown single crystal ZnGa2O4 using a spectroscopic ellipsometry approach. A temperature dependent Cauchy dispersion analysis was applied across the transparent spectrum to determine the high-frequency index of refraction yielding a temperature dependent slope of 3.885(2) x 10(-5)K(-1). A model dielectric function critical point analysis was applied to examine the dielectric function and critical point transitions for each temperature. The lowest energy M-0-type critical point associated with the direct bandgap transition in ZnGa2O4 is shown to red-shift linearly as the temperature is increased with a subsequent slope of -0.72(4) meV K-1. Furthermore, increasing the temperature results in a reduction of the excitonic amplitude and increase in the exciton broadening akin to exciton evaporation and lifetime shortening. This matches current theoretical understanding of excitonic behavior and critically provides justification for an anharmonic broadened Lorentz oscillator to be applied for model analysis of excitonic contributions. Published under an exclusive license by AIP Publishing.

Automated summary

In this study, the elevated temperature dielectric function properties of melt grown single crystal ZnGa2O4 were investigated using a spectroscopic ellipsometry approach. The results show that the lowest energy critical point associated with the direct bandgap transition in ZnGa2O4 exhibits a red-shift and the excitonic amplitude decreases while the exciton broadening increases with increasing temperature.