Effects of heat treatment on diffusion of Cu atoms into CdTe single crystals

Angular dependence of x-ray fluorescence and x-ray absorption fine structur e techniques have been used to study the diffusion of Cu atoms into the pho tovoltaic material CdTe. Depth profile, effective valency, and local struct ure of Cu atoms in a Cu-doped single crystal of CdTe were investigated befo re and after a second heat treatment. Enhanced Cu diffusion into the CdTe s ingle crystal was observed as a result of heating at a moderate temperature around 200 degrees C, resulting in a redistribution of the Cu impurities t hrough a broader depth profile. Some of the Cu atoms are believed either to form small complexes with Te or occupy interstitial sites in the host but accompanied by a large local lattice distortion while others substitute for Cd on the cation sites. The results thus demonstrate that these nondestruc tive x-ray characterization methods are useful for probing microstructural changes in CdTe photovoltaic materials/devices in which some Cu-containing compounds are used as back contacts. (C) 2000 American Institute of Physics . [S0003-6951(00)03625-1].