Evolution of N defect states and optical transitions in ordered and disorderedGaP1−xNx alloys

Abstract

We show using an sp3s* tight-binding model that the band anti-crossing (BAC) model describeswell the evolution of the lowest N-related conduction states in orderedGaP1−xNx alloys, includingthe evolution of the Γ character with increasing x. We obtain a good description of the lowest conduction states in disorderedGaPN structures by explicitly treating the interaction between the GaP hostΓ conduction band minimum and defect states associated with a randomdistribution of N atoms. We find a very similar value for the totalΓ character mixed into the N levels in the ordered and disordered cases, but a wider distribution of stateswith Γ character in the disordered case. We show that the band gap reduction with increasingcomposition is dominated by the increasing formation of N cluster states. Overall keyfeatures of the band structure can be well described using a modified BAC model whichexplicitly includes the broad distribution of N levels in disordered GaPN alloys.