Influence of cluster states on band dispersion in bulk and quantum well (ultra-)dilute nitride semiconductors

The band-anti-crossing (BAC) model successfully describes many of the electronic properties of GaN_xAs_1-x. Experimental and theoretical studies show a range of resonant defect levels close to the conduction band edge in GaN_xAs_1-x, due to the formation of N complexes which are ignored in the conventional BAC model. The consequences of these resonant levels for the band dispersion are investigated. The rapid increase in N-N pairs with N composition (∝x²) is shown to have little effect on the calculated room-temperature band-edge dispersion, but modifies the low-temperature band dispersion with increasing x. For low temperatures, it is shown that at low N composition (0.001≤x≤0.01) the band dispersion is best described using a modified BAC model, which explicitly includes the effects of N-N pairs, while at higher compositions (x>0.01) the effects of longer-range N-N interactions need also to be considered. The consequences of this are analysed for the predicted evolution of band dispersion with x in magneto-tunnelling experiments.