Temperature- and Pressure-Dependent Photoluminescence Emission of Bulk GaSe0.5Te0.5 Alloy

In this study, we conduct a comprehensive investigation into the temperature and pressure dependencies of photoluminescence (PL) in a bulk GaSe0.5Te0.5 alloy. By using density functional theory (DFT) calculations and experimental measurements, we identify and distinguish the contributions of free excitons and indirect transitions to the PL spectrum. Our analysis reveals a nonlinear redshift for these transitions over the temperature range of 90-667 K, evolving in accord with the modified Varshni equation. We observe a pronounced influence of electron-phonon coupling in the GaSe0.5Te0.5 alloy compared to that of GaTe and GaSe crystal structures. Below 180 K, we detect the emergence of new broad bands associated with bound excitons and radiative recombination of trap states. Furthermore, by employing the Arrhenius plots, we determine activation energies for nonradiative recombination of the indirect and free exciton transitions. Concerning the pressure dependence of the PL spectra, the free exciton and indirect transitions undergo a linear redshift within the specific pressure range of 0.3 to 4.3 GPa, accompanied by a continuous reduction in PL intensity, leading to complete quenching at 4.8 GPa. This phenomenon is attributed to a direct-to-indirect band gap crossover. Pressure-dependent band structure calculation via DFT supports this assumption and shows a further metallization of the GaSe0.5Te0.5 alloy at similar to 8.0 GPa. This study sheds new light on understanding the optical properties of the GaSe0.5Te0.5 alloy under extreme pressure and temperature conditions, thereby opening avenues for tailored applications and guiding future research efforts in this field.