A near-field scanning optical microscopic study was made of S interdiffusion in polycrystalline heterojunctions. The diffusion of S from CdS to CdTe led to the formation of a CdTeS ternary phase. Because the band-gap of CdTeS varied with the S composition, it was possible to combine near-field scanning optical microscopy with a tunable laser source and identify S-rich regions in the CdTe layer. The S composition was found to be highly non-uniform, and was frequently greater along grain boundaries than in the grain centres. This indicated that the grain boundaries were locations of enhanced interdiffusion.

Evidence for Grain-Boundary Assisted Diffusion of Sulfur in Polycrystalline CdS/CdTe Heterojunctions M.K.Herndon, A.Gupta, V.Kaydanov, R.T.Collins: Applied Physics Letters, 1999, 75[22], 3503-5