Cu K-edge X-ray fine structure changes in CdTe with CdCl 2 processing

Abstract

We have used the MR-CAT beamline of the Advanced Photon Source at Argonne National Laboratory to study the fine structure in the Cu K-edge X-ray absorption in 3 μm thick polycrystalline films of CdTe on fused silica. About 4 nm of evaporated Cu is diffused either with or without prior vapor CdCl 2 treatments in dry air. Cu absorption is monitored through the Cu K α fluorescence using a 13-element Ge detector. The absorption fine structure indicated predominantly Cu 2Te when Cu was diffused into the as-deposited CdTe film but a Cu x O environment when Cu was diffused after the vapor CdCl 2 treatment. We believe most of the diffused Cu decorates grain boundaries as oxides, consistent with the low doping densities typically observed in CdTe solar cells. The significance for grain boundary passivation will be discussed.