Distinguishing quantum dot-like localized states from quantum well-like extended states across the exciton emission line in a quantum well

TL;DR

This study uses advanced spectroscopy to identify the energy boundary that separates localized quantum dot-like excitons from mobile quantum well-like excitons in a high-quality GaAs quantum well, enhancing understanding of exciton localization.

Contribution

It introduces a spectroscopic method to distinguish localized from extended excitonic states in quantum wells based on sign changes in ECPL signals.

Findings

Identification of the excitonic mobility edge energy.

Observation of complementary ECPL signal behavior around the PL peak.

Evidence of localized and extended excitonic states coexistence.

Abstract

We have closely examined the emission spectrum at the heavy-hole exciton resonance in a high-quality GaAs multi-quantum well (MQW) sample using picosecond excitation-correlation photoluminescence (ECPL) spectroscopy. Dynamics of the ECPL signal at low and high energy sides of the excitonic photoluminescence (PL) peak shows complementary behavior. The ECPL signal is positive (negative) below (above) the PL peak and it changes sign within a narrow band of energy lying between excitonic absorption and emission peaks. The energy at which this sign change takes place is interpreted as the excitonic mobility edge as it separates localized excitons in quantum dot-like states from mobile excitons in quantum well-like states.