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

Abstract

We present a near-field scanning optical microscopy (NSOM) study of S interdiffusion in polycrystalline CdS/CdTe heterojunctions. S diffusion from CdS into CdTe leads to the formation of a ${\mathrm{CdTe}}_{\text{1−x}}{\mathrm{S}}_x$ ternary phase. Because the band gap of ${\mathrm{CdTe}}_{\text{1−x}}{\mathrm{S}}_x$ varies with S composition, we were able to combine NSOM with a tunable laser source to microscopically identify S-rich regions in the CdTe layer. S composition was found to be very nonuniform and frequently to be greater along grain boundaries than in the grain centers, identifying grain boundaries as locations of enhanced interdiffusion.