Large-scale atomistic simulations demonstrate dominant alloy disorder effects in GaBi$_x$As$_{1-x}$/GaAs multiple quantum wells

TL;DR

This study uses large-scale atomistic simulations to show that alloy disorder significantly influences the electronic and optical properties of GaBi$_x$As$_{1-x}$/GaAs quantum wells, surpassing inter-well coupling effects.

Contribution

It provides a detailed atomistic analysis revealing the dominant role of alloy disorder in GaBiAs quantum wells, highlighting limitations of continuum models.

Findings

Alloy disorder causes strong charge carrier confinement.

Significant broadening of hole energy levels observed.

Disorder effects persist despite variations in quantum well parameters.

Abstract

Bismide semiconductor materials and heterostructures are considered a promising candidate for the design and implementation of photonic, thermoelectric, photovoltaic, and spintronic devices. This work presents a detailed theoretical study of the electronic and optical properties of strongly-coupled GaBi$_x$As$_{1-x}$/GaAs multiple quantum well (MQW) structures. Based on a systematic set of large-scale atomistic tight-binding calculations, our results reveal that the impact of atomic-scale fluctuations in alloy composition is stronger than the inter-well coupling effect, and plays an important role in the electronic and optical properties of MQW structures. Independent of QW geometry parameters, alloy disorder leads to a strong confinement of charge carriers, a large broadening of the hole energies, and a red shift in the ground-state transition wavelength. Polarisation-resolved optical transition strengths exhibit a striking effect of disorder, where the inhomogeneous broadening could exceed an order of magnitude for MQWs, in comparison to a factor of about three for single quantum wells. The strong influence of alloy disorder effects persists when small variations in the size and composition of MQWs typically expected in a realistic experimental environment are considered. The presented results highlight the limited scope of continuum methods and emphasise on the need for large-scale atomistic approaches to design devices with tailored functionalities based on the novel properties of bismide materials.