JKAU: Sci., Vol. 21 No. 1, pp: 13-26 (2009 A.D. / 1430 A.H.) 13 Electrical and Thermal Transport Properties of TlGaSe 2 Single Crystals A.T. Nagat, S.E. Al Garni, F.S. Bahabri, G. Attia 2 , S.R. Al Harbi and A.A. Al Ghamdi 1 Physics Department, Girls Colleges of Education, 1 Physics Department, Faculty of Sciences, King Abdulaziz University, Saudi Arabia, and 2 Physics Department, Fayoum University, Egypt Abstract. The electrical conductivity (σ) and Hall coefficient (R H ) of single crystals prepared by a special modified Bridgman technique have been investigated over the temperature range 245-495 K. Our investigation showed that our samples are p-type conducting. The dependence of the Hall mobility on temperature was presented graphically. The forbidden energy gap was calculated and found to be 2.1 eV whereas the ionization energy of the impurity level was 0.36 eV. The values of the electrical conductivity, Hall coefficient and carrier concentration at room temperature were 1.87 × 10 –6 Ω –1 cm –1 , 3.98 × 10 9 cm 3 C –1 and 1.57 × 10 9 cm –3 respectively. The Hall mobility at room temperature (μ H ) was found to be 7.46 × 10 3 cm 2 V –1 s –1 . Also, the thermoelectric power (TEP) was investigated in the temperature range 271-493 K. The combination of the electrical and thermal measurements in the present investigation makes it possible to find various physical parameters such as mobilities, effective mass, relaxation times, diffusion coefficients and diffusion lengths both for majority and for minority carriers, Also figure of merit was determined. These parameters reveal the general behavior of this semiconductor. Keyword: Hall coefficient, TlGaSe 2 , mobility, thermal properties, electrical properties. 1. Introduction The ternary semiconducting chalcogenide with the formula ABX 2 (A, B represent metal atoms, X represents chalcogen atoms) have been studied intensively in recent years. Recently ternary thallium chalcogenides