Determination of the impact of Bi content on the valence band energy of GaAsBi using x-ray photoelectron spectroscopy

K Collar,J Li,Y Guan,J Humlicek,A S Brown,M Losurdo,W Jiao

doi:10.1063/1.4986751

Abstract

We investigate the change of the valence band energy of GaAs1-xBix (0&lt;x&lt;0.025) as a function of dilute bismuth (Bi) concentration, x, using x-ray photoelectron spectroscopy (XPS). The change in the valence band energy per addition of 1 % Bi is determined for strained and unstrained thin films using a linear approximation applicable to the dilute regime. Spectroscopic ellipsometry (SE) was used as a complementary technique to determine the change in GaAsBi bandgap resulting from Bi addition. Analysis of SE and XPS data together supports the conclusion that ∼75% of the reduction in the bandgap is in the valence band for a compressively strained, dilute GaAsBi thin film at room temperature.

Highlights

GaAs1-xBix is a model dilute III-V alloy system enabling fundamental investigation of the impact of dilute Group V additions on alloy bandgap energy and spin-orbit splitting modifications.[1,2,3,4] Bismuth (Bi) is an isoelectronic impurity in GaAs and its incorporation into the III-V system results in variations in valence and conduction band energies and densities of states.[4]
The energy shift due to strain within the film is calculated, using a linear approximation of the valence band maximum movement with incorporation of Bi for a theoretically free-standing GaAsBi thin film. These findings using x-ray photoelectron spectroscopy (XPS) are corroborated by spectroscopic ellipsometry (SE) measurements of the variation of the bandgap resulting from Bi incorporation
Calculation of the valence band energy change using XPS is based on the energy differences between the As 3d and Ga 3d core-levels and the valence band maximum with respect to the Fermi level

Summary

INTRODUCTION

GaAs1-xBix is a model dilute III-V alloy system enabling fundamental investigation of the impact of dilute Group V additions on alloy bandgap energy and spin-orbit splitting modifications.[1,2,3,4] Bismuth (Bi) is an isoelectronic impurity in GaAs and its incorporation into the III-V system results in variations in valence and conduction band energies and densities of states.[4]. Et al.[7] experimentally measured the valence band and conduction band energies of GaAsBi as a function of Bi content using photoreflectance spectroscopy. Their experimental data agrees well with the BAC prediction with the VCA which predicts changes in both the valence band and conduction band energies. They determined valence band energy changes within a range of 20 to 51meV/ Bi% and 33meV/Bi % for conduction band changes for Bi concentrations up to 7.4%.7. A direct measurement which can discriminate movement in the valence band from the conduction band is necessary for predicting heterojunction energy band alignment.[1,3]

EXPERIMENT

RESULTS AND DISCUSSIONS

CONCLUSIONS