Local, electronic and surface structure of multi-component Fe-doped CdTe(S) systems

Abstract

Local structural and electronic properties around Fe in multi-component Cd0.99Fe0.01Te0.97S0.03 system were studied by means of X-ray absorption fine structure (XAFS). Composition of non-polar (110) surfaces of Cd0.97Fe0.03Te and Cd0.99Fe0.01Te0.97S0.03 systems and mechanism of their oxidation in ambient conditions were studied by Atomic Force Microscopy (AFM) and X-ray Photoelectron Spectroscopy (XPS). It has been found that Fe preferentially substitutes Cd, but due to much smaller covalent radius and preferences for paring with S, it causes local distortion of the host CdTe lattice. The distortion is confined to the Fe-immediate surrounding and the second and third coordination shell atoms are (inside experimental uncertainties) placed at distances expected in CdTe. Although local structure around Fe is well defined in the bulk of both samples, their near-surface region is completely depleted from Fe, and in case of Cd0.99Fe0.01Te0.97S0.03 somewhat enriched in S. Special attention is, therefore, paid to characterization of the near-surface region and evaluation of its composition and structure. To that end we have introduced a general standard-free algorithm for XPS data analysis of the two-layer surface structure (bulk, oxide layer, and the impurity layer). Results of the in-depth composition analysis revealed that despite different bulk composition and impurity layer thickness, underneath the topmost impurity layer lays approximately one monolayer of CdTeO3 which passivates the surface.