Phase diagram of the TlGaS₂–CdS system and optical properties of a TlGaS₂:Cd²⁺ crystal

Chem. Met. Alloys 10 (2017) 142-148

https://doi.org/10.30970/cma10.0369

Lyudmyla Piskach, Galyna Myronchuk, Ganna Makhnovets

The phase diagram of the TlGaS₂–CdS system is of the eutectic type, with the coordinates 1021 K, ~80 mol.% TlGaS₂ / ~20 mol.% CdS. The solid solubility of the components is less than 5 mol.% at 670 K. The optical properties of a single crystal of composition 98 mol.% TlGaS₂ / 2 mol.% CdS, grown by the Bridgman method, were investigated. Absorption measurements were performed in the 100-300 K range with 50 K increments. The bandgap energies for direct (E_gd) and indirect (E_gi) transitions in TlGaS₂:Cd²⁺ were calculated as a function of temperature. They were found to be 2.38 and 2.32 eV at 100 K, and 2.27 and 2.2 eV at 300 K, i.e. the bandgap for indirect optical transitions is smaller than the bandgap for direct transitions. The values of the direct and indirect bandgap energies decrease with increasing temperature, whereas the steepness parameter and Urbach energy increase with increasing temperature in the range 100‑300 K. The Urbach energy was calculated as 163 meV at 100 K and 239 meV at 300 K.

Phase diagram of the TlGaS₂–CdS system.

Keywords

Phase equilibria / Crystal growth / Differential thermal analysis / X-ray diffraction / Urbach energy / Steepness parameter