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

Abstract

We report the elevated temperature (22 °C [Formula: see text] T [Formula: see text] 600 °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) × 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 M0-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.

Formation of Quaternary Zn(Alxga1-X)2o4 Epilayers Driven by Thermally Induced Interdiffusion between Spinel Znga2o4 Epilayer and Al2o3 Substrate

“…However not many studies have discussed these properties for ZnGa 2 O 4 (ZGO) 2 being exposed to high temperatures or the effect of interdiffusion with its substrate. Hilfiker et al have recently reported the dielectric function and interband transitions of melt grown ZGO for temperatures up to 600 • C, where they observed a decrease in bandgap at a slope of − 0.72 meVK − 1 with increasing temperatures [19]. Wang et al studied radio frequency sputtered ZGO thin films on sapphire for temperatures ranging from 500 to 900 • C. They observed an increase in bandgap energy from 4.7 eV to 4.98 eV and improvement in crystal quality with increase in temperature [20].…”