Role of Strain on the Coherent Properties of GaAs Excitons and Biexcitons

TL;DR

This study uses polarization-dependent 2DFTS to investigate how biaxial tensile strain affects the coherent optical properties of excitons and biexcitons in GaAs, revealing strain-induced energy splitting and biexciton formation.

Contribution

It provides new insights into strain effects on excitonic coherence and biexciton formation in GaAs using advanced spectroscopic techniques.

Findings

Strain increases HH/LH exciton peak splitting.

Strain induces asymmetry in off-diagonal coherences.

High strain promotes biexciton formation, including bound LH, HH, and mixed biexcitons.

Abstract

Polarization-dependent two-dimensional Fourier-transform spectroscopy (2DFTS) is performed on excitons in strained bulk GaAs layers probing the coherent response for differing amounts of strain. Biaxial tensile strain lifts the degeneracy of heavy-hole (HH) and light-hole (LH) valence states, leading to an observed splitting of the associated excitons at low temperature. Increasing the strain increases the magnitude of the HH/LH exciton peak splitting, induces an asymmetry in the off-diagonal coherences, increases the difference in the HH and LH exciton homogenous linewidths, and increases the inhomogeneous broadening of both exciton species. All results arise from strain-induced variations in the local electronic environment, which is not uniform along the growth direction of the thin layers. For cross-linear polarized excitation, wherein excitonic signals give way to biexcitonic signals, the high-strain sample shows evidence of bound LH, HH, and mixed biexcitons.