Long-period wurtzite/zinc-blende GaN polytypes as one-dimensional alloys: Impacts of stacking disorder on electronic structure and optical transitions

The electronic structure of wurtzite/zinc-blende GaN polytypes is investigated by treating the stacking sequences of hexagonal and cubic bilayers as one-dimensional pseudo-binary alloys. Using an advanced atomistic empirical tight-binding scheme that is polytype-transferable, we analyze the impact of stacking disorder, namely short-range order, and internal electric polarization on the bandgap, the carrier localization, and the optical transitions. It is pointed out that simple Ising-type models fail to capture the electronic structure of long-period polytypes due to their inability to account for quantum confinement and polarization-induced Stark effects. We also reveal that clustering of cubic or hexagonal bilayers significantly reduces the bandgap, enhances carrier localization, and decreases the optical transitions, an effect dramatically amplified by the internal polarization fields in the insulating regime. These results suggest that stacking disorder in GaN polytypes is not merely a defect but can be viewed as a potentially tunable degree of freedom, behaving analogously to compositional fluctuations in conventional chemical alloys.