Micro-Raman spectroscopy on polycrystalline CuInSe2 formation

Abstract

The crystalline formation of CuInSe2 thin films has been investigated using micro-Raman spectroscopy and AES composition analysis. It is confirmed that the Raman peaks are strongly dependent on the surface morphology and the Cu:In:Se ratio. In the films annealed at 315 °C, crystalline grains larger than 2 μm show Raman peaks at 174 cm-1 and 258 cm-1. The In content is very low and the Cu:Se ratio is about 1:1 in these grains. The low In concentration is thought to be due to the formation of In2O3 on the surface. On the other hand, random structures of 1-2 μm grains found in films annealed at temperatures below 305 °C show peaks at 174 cm-1 and 186 cm-1 instead of 258 cm-1 and have a Cu:In:Se ratio of 1:1:3-4. Thus the 186 cm-1 peak is thought to be related to a Cu, In-deficient phase when compared to stoichiometric CuInSe2. The optimum annealing condition was found by analyzing the Raman spectra and composition of different crystalline CuInSe2 grains. Films annealed under this condition exhibited a clear Raman peak at 174 cm-1 and consisted of clusters of crystals less than 1 μm in size.