Impact of disorder on the optoelectronic properties of GaN${}_y$As${}_{1-x-y}$Bi${}_x$ alloys and heterostructures

We perform a systematic theoretical analysis of the nature and importance of alloy disorder effects on the electronic and optical properties of GaN${}_y$As${}_{1-x-y}$Bi${}_x$ alloys and quantum wells (QWs), using large-scale atomistic supercell electronic structure calculations based on the tight-binding method. Using ordered alloy supercell calculations we also derive and parametrise an extended basis 14-band $\mathbf{\text{k}}$$\cdot$$\mathbf{\text{p}}$ Hamiltonian for GaN${}_y$As${}_{1-x-y}$Bi${}_x$. Comparison of the results of these models highlights the role played by short-range alloy disorder – associated with substitutional nitrogen (N) and bismuth (Bi) incorporation – in determining the details of the electronic and optical properties. Systematic analysis of large alloy supercells reveals that the respective impact of N and Bi on the band structure remain largely independent, a robust conclusion we find to be valid even in the presence of significant alloy disorder where N and Bi atoms share common Ga nearest neighbours. Our calculations reveal that N- (Bi-) related alloy disorder strongly influences the conduction (valence) band edge states, leading in QWs to strong carrier localisation, as well as inhomogeneous broadening and modification of the conventional selection rules for optical transitions. Our analysis provides detailed insight into key properties and trends in this unusual material system, and enables quantitative evaluation of the potential of GaN${}_y$As${}_{1-x-y}$Bi${}_x$ alloys for applications in photonic and photovoltaic devices.