The effect of In doping in CdS/CuInSe2 heterojunction formation: A photoemission investigation

Synchrotron radiation soft x‐ray photoemission spectroscopy was used to investigate the development of the electronic structure at the CdS(In)/CuInSe2 heterojunction interface. In‐doped CdS overlayers were deposited in steps on single‐crystal n‐type CuInSe2 at 250 °C. Results indicate that the CdS(In) 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(In)/CuInSe2 heterojunction valence band discontinuity and the consequent heterojunction band diagram as a function of In dopant concentration. We measured a valence band offset ΔEv=0.3 eV, independent of In doping.