Evidence for grain-boundary-assisted diffusion of sulfur in polycrystalline CdS/CdTe heterojunctions

We present a near-field scanning optical microscopy (NSOM) study of S inter diffusion in polycrystalline CdS/CdTe heterojunctions. S diffusion from CdS into CdTe leads to the formation of a CdTe1-xSx ternary phase. Because the band gap of CdTe1-xSx varies with S composition, we were able to combine N SOM with a tunable laser source to microscopically identify S-rich regions in the CdTe layer. S composition was found to be very nonuniform and freque ntly to be greater along grain boundaries than in the grain centers, identi fying grain boundaries as locations of enhanced interdiffusion. (C) 1999 Am erican Institute of Physics. [S0003-6951(99)00348-4].