Composition of oxide on CdZnTe surface and changes caused by X-ray exposure
摘要
Soft X-ray photoemission spectroscopy has been used to depth profile the composition of 2.8-nm-thick surface oxide layers on ozone-oxidized Cd0.9Zn0.1Te (111)A single-crystal surfaces. Chemical shifts in the Te 3d and 4d photoemission peaks are analyzed to infer the oxidation state of Te as a function of depth below the surface of the oxidized samples. We conclude that the free surface of the as-prepared oxide is terminated with a monolayer of CdO and that the layers below the surface are incompletely oxidized, containing small concentrations of elemental Te and CdTe. Following extended X-ray exposure, the oxide loses Cd and oxygen and is terminated with a monolayer of elemental Te, while the layers below the surface become fully oxidized. Exposure to X-rays with photon energy just above the O K-edge is found to accelerate the radiation-induced changes in composition by a factor of 4 compared with exposure to radiation with photon energy just below the O K-edge. The estimated X-ray flux in a medical computed tomography imager is too small to cause significant changes in oxide layer composition in a CZT detector over the operational lifetime of the imager.