Thermal oxide on CdSe

Abstract

X-ray photoelectron spectroscopy (XPS) has been used to characterize the thin thermal oxide film grown on single crystal CdSe(0001) and polycrystalline CdSe by exposure to O2 (dry air) at 350 °C. SeOx species, where x=2,3, are clearly identified by a 5 eV shift of the Se 3d3/2,5/2 peaks to higher binding energy. A very weak shift to lower binding energy is observed for the Cd peaks. The positions of the Cd and O peaks do not match those found for the known cadmium oxides, CdO and CdO2. Instead, it is proposed that the Cd bound oxygen atoms occupy substitutional Se sites. The presence of Cd bound oxygen can also be inferred from the intensities of the SeOx, Cd, and O peaks. Raman spectroscopy confirms the existence of O in Se substitutional sites. Angle-resolved XPS is used to determine the thickness of the oxide and the relative amount of SeOx and Cd bound oxygen. The XPS data are consistent with an 8–9 Å thick oxide where ∼60% of the oxygen is bound to Se and ∼40 is bound to Cd. The data show that the oxide structure contains two layers; a passivation layer made of the SeOx species and, underneath, a layer containing oxygen in Se substitutional sites.