Unusual bandgap bowing in highly mismatched ZnOS alloys: Atomistic tight-binding band anti-crossing model

Abstract

An atomistic band anticrossing (BAC) model is developed and used to study “unusual bowing” in energy bandgap and its dependence on the material composition in minority O anion-alloyed ZnS (ZnS1−xOx) and minority S anion-alloyed ZnO (ZnO1−xSx) highly mismatched alloys. For dilute O in ZnS1−xOx, it is found that the bandgap decreases as the O composition is increased. A “down-shift” in the conduction band edge (CBE) of host ZnS, which arises from an interaction between the CBE and the localized O defect state, is identified as the root cause. However, the reduction in bandgap as a function of dilute S composition in the ZnO1−xSx alloy follows an “up-shift” in the valence band edge (VBE) of hos..