USE OF X-RAY PHOTOELECTRON-SPECTROSCOPY TO INVESTIGATE THE DEPOSITION OF METAL OVERLAYERS ONTO THE CLEAN CLEAVED CDS SURFACE

X-ray photoemission spectroscopy (XPS) is used to study the deposition of a range of metals onto both the clean cleaved and air exposed surfaces of n-type CdS. Al, Co and Pd are clearly observed to react with the CdS surface to form a metal sulphide together with metallic Cd. There is no evidence for metal sulphide formation after the evaporation of Au, Ag or Sb. The Sn 3d core level emission for Sn on CdS shows two components, indicative of SnSn and SnS bonding. However, in this case, there is no sign of metallic Cd being formed with increasing Sn coverage. Our XPS spectra also allow us to measure the initial Fermi level movement (band bending) which occurs as the metal/CdS interface is being formed. Schottky barrier heights obtained from XPS measurements show the same trend as barrier heights determined from current-voltage characteristics. Finally, by considering the contribution of defects to the electrical properties of metal/CdTe and metal/CdS diodes, we assess the relevance of these studies to the nature of electrical barriers at metal/CdS interfaces. © 1990.