Effect of deposition temperature on the optical and structural properties of as-deposited CulnS_2 films

摘要

Structural and optical properties of thin films CuInS_2 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 ℃. We obtain CuInS_2 layers with high structural quality by growing at T_s ≈ 140 ℃ with the presence of an amorphous component and at T_s ≈ 240 ℃ with formation of In and Cu_7In_4 as minority phases. From the optical transmission and reflection an optical absorption coefficient of 3 × 10~4-10~5 cm~(-1) for λ ＜ 1000 nm was calculated for the films deposited at T_s > 200 ℃. 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 ≈ 140 ℃ and T_s ≈ 240 ℃ yield maxima of the grain size and minima of the surface roughness.