Studies of virtually insoluble systems with large interfacial area: CdTe-ZnO

Exchange of matter at CdTe/ZnO heterojunctions was studied in (a) polycrystalline CdTe with dispersed ZnO and (b) single crystals of CdTe in contact with compressed ZnO powders. Scanning electron microscopy with electron microprobe analysis, differential thermal analysis and X-ray diffraction were the experimental techniques utilized to investigate CdTe-ZnO. Samples (a) were heated to 950degreesC or 1110degreesC and (b) to 950degreesC, for 60 min. ZnxCd(1-x)Te formed at CdTe/ZnO interfaces by thermal treatment. The magnitude of the diffusion of Zn in CdTe was estimated and found in agreement with earlier studies. A superlattice, attributable to ordering of zinc in CdTe, was suggested by preliminary single crystal XRD data from ZnxCd(1-x)Te microcrystals. Diffusion of zinc was faster in single crystals than in polycrystals. The study of CdTe with dispersed ZnO complements a series of studies on dispersed second phase materials. The work was carried out over the last 30 years at Professor J.B. Wagner's research laboratories, with the following outcome: Transport depended on surface area of the dispersed phase and of the matrix. Changes in electrical and mass transport, and in phase transformation temperatures, due to the presence of dispersoids, were consistent with an interpretation by the space charge model. The present results on the chemistry and microstructure CdTe with dispersed ZnO, in conjunction with the knowledge accrued on transport in dispersed second phase systems, indicate a potential application of this material in photovoltaic devices. (C) 2002 Elsevier Science B.V. All rights reserved.