Influence of Bi Alloying on GaAs Valence Band Structure

TL;DR

This study investigates how bismuth alloying affects the valence band structure of GaAs, revealing the role of Bi p-orbitals in enhancing spin-orbit splitting through combined experimental and theoretical analysis.

Contribution

It provides the first high-resolution ARPES measurements of GaAsBi alloys and clarifies the origin of Bi-induced spin-orbit splitting enhancement.

Findings

Bi alloying shifts valence bands upward

Bi p-orbitals are key to spin-orbit splitting increase

Experimental and theoretical results agree on Bi's role

Abstract

Bi alloying is predicted to transform GaAs from a semiconductor to a topological insulator or semi-metal. To date, studies of the GaAs$_{1-x}$Bi$_x$ alloy band structure have been limited, and the origins of Bi-induced enhancement of the spin-orbit splitting energy, $\Delta_\mathrm{SO}$, are unresolved. Here, we present high-resolution angle-resolved photoemission spectroscopy (ARPES) of droplet-free epitaxial GaAs$_{1-x}$Bi$_x$ films with $x_{\mathrm{Bi}}$ = 0.06. In addition to quantifying the Bi-induced shifts of the light-hole and heavy-hole valence bands, we probe the origins of the Bi-enhanced $\Delta_\mathrm{SO}$. Using exact-two-component density functional theory calculations, we identify the key role of Bi p-orbitals in the upward shift of the light-hole and heavy-hole bands that results in the Bi-enhanced $\Delta_\mathrm{SO}$.