Effect of deposition temperature on the optical and structural properties of as-deposited CuInS2 films

Structural and optical properties of thin films CuInS2 grown by thermal evaporation have been studied relating the effects of substrate heating conditions of these properties. The depositions were carried out at substrate temperatures in the range 65-295 degrees C. We obtain CuInS2 layers with high structural quality by growing at T-s approximate to 140 degrees C with the presence of an amorphous component and at T-s approximate to 240 degrees C with formation of In and Cu7In4 as minority phases. From the optical transmission and reflection an optical absorption coefficient of 3 x 10(4)-10(5) cm(-1) for lambda < 1000 nm was calculated for the films deposited at T-s > 200 degrees C. Analysis of the absorption coefficient data revealed the existence of several energy gaps, direct and forbidden direct gaps. The direct gaps lie between 1.38 and 2.20 eV and the forbidden direct gaps are in the 0.61-1.97 eV range. The effect of the substrate temperatures on the grain size and surface roughness has been studied. It has been shown that the substrate temperatures T-s approximate to 140 degrees C and T-s approximate to 240 degrees C yield maxima of the grain size and minima of the surface roughness.