Defects study in zinc blende ZnS utilizing optimized hybrid functional

Abstract

Due to its wide band gap and widespread availability in single crystals as well as thin film, zinc sulfide (ZnS) has been applied in many areas. Unfortunately, experimental studies alone are not always sufficient to understand the electronic properties of semiconductors, especially their intrinsic point defects. It is thus necessary to perform theoretical calculations along with the characterization experiments to elucidate their defect characteristics. Density functional theory (DFT) with (semi)local exchange correlation is not often appropriate for describing defects in wide band gap semiconductors, while hybrid functional that do not enforce generalized Koopmans theorem (gKT) are not entirely reliable for predicting the properties of point defects in semiconductors. In this study, we have tuned exact-exchange parameters of hybrid functional to not only reproduce the experimental band gap but also satisfy the gKT for zinc blende (ZB) ZnS. With the new optimized hybrid functional, we study the intrinsic defects in ZB ZnS. Using this optimized hybrid functional we study the intrinsic defects of ZB ZnS. The results show that intrinsic defects have deep charge-transition levels. Among these defects, the zinc vacancy (Znvac) is energetically preferable in a n-type undoped sample either in Zn-rich or S-rich conditions. The calculated emission energy by the combination of an electron from the conduction band minimum and a trapped hole at Znvac2- is 3.17 eV. This calculation is the first theoretical result that explains the origin of the deep-blue emission in ZB ZnS.