Theory of the electronic structure of dilute nitride alloys: beyond the band-anti-crossingmodel

Abstract

We use an sp3s* tight-binding Hamiltonian to investigate the band-anti-crossing (BAC) model for diluteGaNxAs1−x alloys. The BAC model describes the strong band-gap bowing at low N compositionx in terms of an interaction between the conduction band edge(E−) and a higher-lying band of localized nitrogen resonant states(E+). We demonstratethat the E− level can be described very accurately by the BAC model, in which wetreat the nitrogen levels explicitly using a linear combination of isolatednitrogen resonant states (LCINS). We also use the LCINS results to identifyE+ in the full tight-binding calculations, showing that at low N compositionE+ forms a sharp resonance in the conduction bandΓ-related density of states, which broadens rapidly at higher N composition when theE+ level rises in energy to become degenerate with the larger L-related density of states. Wethen turn to the conduction band dispersion, showing that the two-level BAC modelmust be modified to give a quantitative understanding of the dispersion. Wedemonstrate that the unexpectedly large electron effective mass values observed insome GaNAs samples are due to hybridization between the conduction bandedge and nitrogen states close to the band edge. Finally we show that there isa fundamental connection between the strong composition-dependence of theconduction-band-edge energy and the n-type carrier scattering cross-section inGa(In)NxAs1−x alloys, imposing general limits on the carrier mobility, comparable to the highest measuredmobility in such alloys.