Large configuration-induced band-gap fluctuations in GaN_xAs _1-x alloys

The electronic band structures of GaN_xAs_1-x alloys were investigated versus the nitrogen mole fraction x and the nitrogen atomic configuration. The computational method is based on the sp³s ^* tight-binding technique. Two main nitrogen atomic distributions were considered: (i) the nitrogen atoms grouped in one region to form like a GaN dot inside the GaAs so as to have a maximally N-clustered (MNC) configuration; and (ii) the nitrogen atoms homogeneously distributed over the alloy and, of course, the minimal N-clustered distribution as the maximally As-clustered (MAsC) configuration. The former is found to always have the lowest band gaps. More interestingly, the results show that in the latter distribution the nitrogen atoms introduce resonant states above the conduction-band edge by about 230 meV, which is consistent with the literature, whereas they introduce a deep gap state above the valence-band edge at about 150 meV in the former distribution. As a suitable model for experimental samples, the MAsC configuration, was used to model some available photoluminescence data in the dilute regime.