Growth and Characterization of the Binary Defect Alloy Cu2-xSe and the Relation to II–VI/I–III–VI Heterojunction Formation
AbstractSynchrotron radiation soft x-ray photoemission spectroscopy was used to investigate the development of the electronic structure at the CdS/Cu2Se heterojunction interface. Cu2−xSe layers were deposited on GaAs (100) by molecular beam epitaxy from Cu2Se sources. Raman spectra reveal a strong peak at 270 cm−1, indicative of the Cu2−xSe phase. Atomic force microscopy reveals uniaxial growth in a preferred (100) orientation. CdS overlayers were then deposited in-situ, at room temperature, in steps on these epilayers. Photoemission measurements were acquired after each growth in order to observe changes in the valence band electronic structure as well as changes in the Se3d and Cd4d core lines. The results were used to correlate the interfacial chemistry with the electronic structure and to directly determine the CdS/Cu2−xSe and heterojunction valence band discontinuity and the consequent heterojunction band diagram. These results are compared to the valence band offset (ΔEv) for the CdS/CuInSe2 heterojunction interface.
