Soft X-ray Photoemission Investigation of the CdS/CuInSe2 Hetrojunction Interface

Synchrotron radiation soft X-ray photoemission spectroscopy was used to investigate the development of the electronic structure at the CdS CuInSe₂ heterojunction interface. CdS overlayers were deposited sequentially in steps on steps on single-crystal p- and n-type CuInSe₂ at 250°C. Results indicate that the CdS grows in registry with the substrate, initially in a two-dimensional growth mode followed by three-dimensional island growth as is corroborated by RHEED analysis. Photoemission measurements were acquired after each growth in order to observe changes in the valence band electronic structure as well as changes in the In4d, Se3d, Cd4d and S2p core lines. The results were used to correlate the interface chemistry with the electronic structure at these interfaces and to directly determine the CdS CuInSe₂ heterojunction valence band discontinuity and the consequent heterojunction band diagram.