Novel Method for Growing CdS on CdTe Surfaces for Passivation of Surface States and Heterojunction Formation

Large-grain polycrystalline CdTe was subjected to in situ H2S plasma processing for <30 min at 100 and 200 degrees C. High-resolution x-ray photoemission measurements on the Cd 4d, Te 4d, and S 2p core levels, and the valence band were used to determine the resultant chemical environment of S and the electronic structure at the CdTe surface following plasma processing. Auger electron spectroscopycompositional depth profiling was also used to determine the distribution of S in the near surface region. Furthermore, time-resolved photoluminescence was used to measure carrier lifetimes and, thus, determine the degree of passivation of CdTe surface states. These results provide evidence for a CdS/CdS1-xTex/CdTe heterojunction device structure, as a result of the H2S plasma processing, and areduction in the surface recombination velocity through passivation of surface states. This is a novel method of fabricating CdS/CdTe heterojunction devices.