Band-gap reduction and band alignments of dilute bismide III--V alloys

TL;DR

This study uses hybrid functional calculations to analyze how small amounts of bismuth alter the electronic structure of III--V semiconductors, revealing significant band-gap reduction and band alignment changes with implications for device design.

Contribution

It provides detailed predictions of band structure modifications in dilute bismide III--V alloys, including band-gap reduction, band offset, and potential topological properties, using advanced computational methods.

Findings

Adding Bi raises the valence-band maximum (VBM).

Conduction-band minimum (CBM) is significantly lowered by Bi.

Band-gap reduction is larger in arsenides than in antimonides.

Abstract

Adding a few atomic percent of Bi to III--V semiconductors leads to significant changes in their electronic structure and optical properties. Bismuth substitution on the pnictogen site leads to a large increase in spin-orbit splitting $\Delta_{\rm SO}$ at the top of the valence band ($\Gamma_{8v}-\Gamma_{7v}$) and a large reduction in the band gap, creating unique opportunities in semiconductor device applications. Quantifying these changes is key to the design and simulation of electronic and optoelectronic devices. Using hybrid functional calculations, we predict the band gap of III--Vs (III=Al, Ga, In and V=As, Sb) with low concentrations of Bi (3.125\% and 6.25\%), the effects of adding Bi on the valence- and conduction-band edges, and the band offset between these dilute alloys and their III--V parent compounds. As expected, adding Bi raises the valence-band maximum (VBM). However, contrary to previous assumptions, the conduction-band minimum (CBM) is also significantly lowered, and both effects contribute to the sizable band-gap reduction. Changes in band gap and $\Delta_{\rm SO}$ are notably larger in the arsenides than in the antimonides. We also predict cases of band-gap inversion ($\Gamma_{6c}$ below $\Gamma_{8v}$) and $\Delta_{\rm SO}$ larger than the band gap, which are key parameters for designing topological materials and for minimizing losses due to Auger recombination in infrared lasers.