Effects of vacancy defects on the electronic structure and optical properties of ZnSe and ZnSe:Cr.

The transition metal Cr-doped ZnSe semiconductor is a kind of material that can realize laser output in the mid-infrared band and has broad application prospects in the fields of air monitoring, surgery, optical communication, industrial production, and national defense. In this work, the electronic structure, optical properties, and stability of ZnSe and ZnSe:Cr with vacancy defects introduced at Zn and Se sites were investigated. The vacancy affects the internal structure of the ZnSe crystal, where the Se vacancy increases the bandgap, but the Ze vacancy changes the semiconductor properties of ZnSe. Affected by the vacancy of adjacent atoms, the impurity bands produced by in ZnSe:Cr crystals have undergone changes in their position and degeneracy in the bandgap. In terms of optical properties, Zn vacancy leads to a more significant red shift (5375.37-6447.55 nm) of ZnSe:Cr absorption peak position than Se vacancy (620.48 nm). Zn vacancy and Se vacancy made the absorption peak of ZnSe red shift (2250.84 nm) and blue shift (144.71 nm), respectively. Meanwhile, Zn vacancy improved the refractive index and reflectivity of the crystal significantly. Our results suggest that vacancy defects can affect the luminescence range of ZnSe and ZnSe:Cr crystals. This phenomenon can be used to judge whether the crystals are defective or not, and long-wave laser can also be obtained from defective crystals.