Long-range spatial correlations in the exciton energy distribution in GaAs/AlGaAs quantum-wells

TL;DR

This study reveals that well-width fluctuations in GaAs/AlGaAs quantum wells exhibit long-range spatial correlations both laterally and vertically, linked to surface mound structures, indicating intrinsic growth properties.

Contribution

It uncovers the existence of long-range correlations in well-width fluctuations in quantum wells, a novel insight into epitaxial growth effects.

Findings

Long-range correlations in well-width fluctuations are observed.

Correlations exist both laterally and vertically.

Surface mound structures are linked to these fluctuations.

Abstract

Variations in the width of a quantum well (QW) are known to be a source of broadening of the exciton line. Using low temperature near-field optical microscopy, we have exploited the dependence of exciton energy on well-width to show that in GaAs QWs, these seemingly random well-width fluctuations actually exhibit well-defined order -- strong long-range correlations appearing laterally, in the plane of the QW, as well as vertically, between QWs grown one on top of the other. We show that these fluctuations are correlated with the commonly found mound structure on the surface. This is an intrinsic property of molecular beam epitaxial growth.