Temperature dependence of bandgap and exciton photoreflectance in layered gallium telluride

Carlo Sta. Maria^1*, Po-Hung Wu², Chien-Chih Lai¹, Yuan-Ron Ma¹

¹Department of Physics, National Dong Hwa University, Hualien, Taiwan
²Department of Electrical Engineering, National Dong Hwa University, Hualien, Taiwan

* Presenter:Carlo Sta. Maria, email:carlostamaria14@gmail.com

This work investigates the energy transitions and the emission of layered gallium telluride (GaTe) using photoreflectance (PR) and photoluminescence (PL) spectroscopies. The room temperature PR spectrum has two energy features at 1.656 eV and 1.647 eV, which corresponds to the band-edge (BE) transition and the free exciton (FX) energy. The PL spectrum, on the other hand, has one main peak at ~ 1.65 eV, which corresponds to the FX emission. To further analyze the optical band gap and the origin of the PL emission, temperature-dependent PR and PL measurements were carried out. Both the PR and PL spectra have the same features or peak at cryogenic temperatures. Using Varshni’s equation for temperature-dependence of the energy transitions, the estimated E₀ (energy at 0 K) of the PR features for the BE and FX are 1.794 eV and 1.776 eV, respectively, while the PL peak has an E₀ of 1.778 eV. This indicates that the PL emission of GaTe does not originate directly from the BE. Instead, it first goes to the lower-energy FX state before the electron-hole recombination, resulting in an emission that has lower energy than the BE transition.

Keywords: Layered gallium telluride, photoreflectance, band-edge transition, free exciton