Formation and characterization of CdSxTe1-x alloys prepared from thin film couples of CdS and CdTe

Alloying between CdS and CdTe at the CdS/CdTe interface is a function of the growth temperature and post-deposition CdCl₂ heat treatment (HT). In devices prepared by different techniques, Te-rich CdS_xTe_1-x alloys with x = 0.04 to 0.08 have been identified. We present our work on thin-film couples of CdS and CdTe, which can withstand higher level of CdCl₂ treatment without the adhesion problems typically encountered in the regular device structure. CdS films with a thickness of ∼100 nm were deposited by chemical-bath deposition on glass/SnO₂ substrates, and CdTe films with a thickness of 300 and 800 nm were deposited by close-spaced sublimation. The samples were treated in the presence of vapor CdCl₂ at 400°-450°C for 5 min. X-ray diffraction and optical analysis of the samples showed that S content in the CdS_xTe_1-x alloy increased systematically with the CdCl₂ HT temperature. CdS_xTe_1-x alloy with x = 0.14 was identified for the samples treated at 430°C, which is much higher than expected from the miscibility gap at 430°C.