Some Optical Properties of Layer-Type Semiconductor GaTe

Abstract

Some optical properties of GaTe single crystals, such as absorption coefficient, photoconductivity and reflectivity, have been measured. The crystal is usually p-type with carrier density 10¹⁶ cm⁻³, mobility 15 cm²/volt·sec and resistivity 20Ω·cm at room temperature. In the measurement of the photoconductivity, a minimum of the photoresponse corresponding to the strong line structure of absorption is observed and therefore the line structure is interpreted to be due to the formation of excitons. The energy gap and exciton binding energy are deduced from the shape of the absorption curve near the edge. The energy gap is 1.797 eV at 77°K and 1.700 eV at 300°K and the temperature coefficient ∂E_g⁄∂T is found to be −4.35×10⁻⁴eV/°K. The exciton binding energy and the reduced effective mass associated with conduction and valence band are 0.025 eV and 0.089 m₀, respectively. The reflectivity is found to change rapidly at the photon energy corresponding to the exciton absorption.