Abstract. We report the results of experimental studies for the optical absorption in TlGaSe 2 :Zn 2+ single crystals grown using a modified Bridgman-Stockbarger technique. The absorption measurements at different temperatures are performed with the steps 50 K. The analysis of the experimental data yield in the absorption coefficients of TlGaSe 2 :Zn varying from 20 to 800 cm -1 in the temperature region 100-300 K. Direct and indirect bandgap values for TlGaSe 2 :Zn 2+ are calculated as functions of temperature. These values are respectively equal to 2.22 and 2.04 eV at 100 K. It is revealed that the spectral dependences of the absorption coefficient in the region 60-130 cm -1 follow the Urbach rule, whereas the corresponding steepness parameter and the Urbach energy increase with increasing temperature.
The phase diagram of the TlGaS 2-CdS system is of the eutectic type, with the coordinates 1021 K, ∼ ∼ ∼ ∼80 mol.% TlGaS 2 / ∼ ∼ ∼ ∼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.% TlGaS 2 / 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 TlGaS 2 :Cd 2+ 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.
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