Optical properties of Cd1−xZnxTe films in a device structure using variable angle spectroscopic ellipsometry

Abstract

The optical properties of polycrystalline Cd1−xZnxTe alloy thin films in device structures are reported for energy from 0.8 to 4.6 eV. Cd1−xZnxTe alloy thin films with x from 0 to 1 were deposited on glass/indium-tin-oxide (ITO)/CdS substrates by coevaporation from CdTe and ZnTe sources and were characterized by variable angle spectroscopic ellipsometry, energy dispersive x-ray spectroscopy, and x-ray diffractometry. The Cd1−xZnxTe films are single phase with a zincblende crystal structure over the entire alloy range. The Cd1−xZnxTe optical constants were determined using a multilayer optical model incorporating the optical constants of glass, ITO and CdS, determined independently from glass, glass/ITO, and glass/ITO/CdS specimens. The optical constants of the Cd1−xZnxTe thin films are comparable to literature values reported for single crystals, indicating that the polycrystalline nature of the films does not measurably alter the optical constants. A semiconductor alloy model for determining the composition of CdxZn1−xTe alloy films is developed using the optical data obtained from the analysis. This alloy model can be used to evaluate compositional grading and the effects of Cd1−xZnxTe film processing.