Alloy disorder and partial order effects on the bowing parameter of CdZnTe semiconductors

Abstract

Cd1−xZnxTe (CZT) is an important semiconductor for applications in radiation detectors. As the Zn concentration x varies, the bandgap of CZT changes accordingly, and this composition-dependent behavior is commonly described by a bowing parameter b that is independent of x. For CZT alloys, however, the measured b exhibits a broad range of values, from very small to near unity, across CZT samples fabricated by different methods, experimental conditions, and labs. Such a large variation likely originates from the microscopic details of the atomic structure in CZT. In this study, first-principles modeling is performed to theoretically investigate how atomic arrangements influence the bowing parameter. It is found that the large variation in the bowing parameter may arise from uneven atomic distributions in partially ordered configurations, which represent intermediate states between fully disordered and fully ordered alloy structures. In particular, a completely random Zn distribution is observed to yield small bowing parameters, whereas partially ordered structures tend to give rise to much larger values. By comparing ZnTe/CdTe interface models with fully disordered models, valuable insights are provided into the relationships among atomic arrangements, atomic-scale inhomogeneity, and the electronic properties of CZT. Finally, the disorder-limited resistance values of the CZT alloy models are calculated and compared.