Optical absorption edge and Urbach tails for Tl_0.999GaPr_0.001Se₂, <span style="font-size:14.0pt;line-height:115%;font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman";mso-ansi-language:EN-IN;mso-fareast-language: EN-IN;mso-bidi-language:HI">Tl_0.995GaPr_0.005Se₂ and TlGaSe₂</span>

Abstract

647-653TlGaSe2, Tl0.999GaPr0.001Se2, and Tl0.995GaPr0.005Se2, single crystals were grown by the Stockbarger method. The absorption measurements were carried out in these samples in temperature range 10-320 K with a step of 10K. The phonon energies calculated in TlGaSe2, Tl0.999GaPr0.001Se2 and Tl0.995GaPr0.005Se2 are 60.0±5, 55.0±5 and 130.0±5 meV respectively. The first defect levels (n=1) have been found as 2.259, 2.235, 2.200 and 2.149 eV for Tl0.999GaPr0.001Se2 and 2.254, 2.225, 2.189 and 2.149 eV for Tl0.995GaPr0.005Se2 at 10,100, 200 and 300 K. At 300 K direct band gap of TIGaSe2 is 2.156 eV, and indirect band gap is 2.075 eV. There are abrupt changes in the Urbach energy peaks for Tl0.999GaPr0.001Se2 at 100 and 200 K, and Tl0.995GaPr0.005Se2 at 200 and 260 K. There is an abrupt change in the σ0 values for Tl0.999GaPr0.001Se2 and Tl0.995GaPr0.005Se2 in the temperature range 140-180 K and 220-260 K. These temperatures obtained from the changing of Urbach energy and σ0 values may be phase transition temperatures