Surface composition of Cd_1–xFe(Mn)_xTe_1–ySe_y systems exposed to air

Using X–ray induced Photoelectron Spectroscopy, Time–of–Flight Secondary Ion Mass Spectrometry and Atomic Force Microscopy we have investigated elemental composition, structure and oxidation process taking place at the surfaces of polycrystalline Cd_0.99Fe_0.01Te_0.97Se_0.03 and Cd_0.95Mn_0.05Te_0.97Se_0.03 systems stored in ambient conditions. The surface oxidation destroys the native CdTe matrix and provokes substantial atomic rearrangement in the first few atomic layers. The near–surface region of both systems is enriched in Cd and to some extent Te–deficient, but the surface structure, morphology and the native oxide composition are all found to be considerably different. In Cd_0.99Fe_0.01Te_0.97Se_0.03 system both Fe and Se dopants diffuse into the bulk and oxidation of its surface results in formation of a thin CdTeO₃ layer which covers the CdTe matrix. In Cd_0.95Mn_0.05Te_0.97Se_0.03 system oxygen–rich atmosphere triggers Mn and Se out–diffusion and the nonuniform oxide layer predominantly consists of MnO and a small amount of Te–oxide which both lay underneath a thin layer of metallic Cd segregated at the top of the surface.