Direct and indirect transitions in copper telluride thin films

Abstract

Transmission and reflection at nearly normal incidence of vacuum-deposited thin films of different thicknesses ranging from 100 to 3000 Å maintained at room temperature on glass or quartz substrates were measured in the wavelength range from 0.295 to 2.5 μm. The absorption coefficients α were computed for different thicknesses. The analysis of the absorption coefficient data revealed the existence of two optical transition mechanisms: an allowed direct transition with E gd = 1.18 eV and an indirect transition with E gi = 0.82 eV. The frequency dependences of the optical constants n, k, ε and ε are also given. The high frequency dielectric constants ε and ε as estimated from extrapolation of the curves to the high frequency range are 17 and 9 respectively.