| MBE growth of single crystal CdS was performed on CdTe(111) and the interfaces formed between CdS and CdTe were studied using x-ray photoelectron spectroscopy in order to determine the band offsets at these interfaces. Despite the lattice mismatch existent between CdS and CdTe, the (111) surface of the CdTe substrate is promoting the growth of CdS with a hexagonal structure. The epitaxial relationship found between wurtzite CdS and zinc-blende CdTe(111) is CdS[011¯0]//CdTe[112¯]) and CdS[0001]//CdTe[111].; An interface model based on the XPS results is proposed for the stacking arrangements CdTe/CdS/CdTe(111) when using different substrate polarities. In the case of using CdTe(111)B substrates, the interface between CdS and CdTe(111)B is formed by diffusion of S into CdTe and subsequent formation of S-T bonds leading to a TeSx compound. Charge accumulation at the interface is prevented by formation of Cd antisites. Similarly at the interface between CdTe and CdS/CdTe(111)B, S-Te bonds are formed leading to a STex compound, hence a smaller chemical shift of Te peaks.; In the case of growth on CdTe(111)A the interface is more abrupt and no Te-S bonds are needed to explain the interface arrangement. Anion-cation bonds and a highly probable S-termination of CdS epilayer lead to formation of CdTe(111)B epilayers grown on CdS/CdTe(111)A. Band offset measurements indicate for both types of interfaces a type-I band alignment. |
