Near-field light emission from dark-states inverted exciton occupations

TL;DR

This paper provides a theoretical analysis of carrier distribution in symmetric quantum dots under continuous excitation, revealing a dark state with unexpectedly high occupation due to suppressed radiative recombination, observable via near-field microscopy.

Contribution

It introduces a novel understanding of dark-state occupations in symmetric quantum dots, highlighting the role of symmetry-induced radiative suppression in carrier trapping.

Findings

Dark state exhibits higher carrier density than the lowest level.

Carrier trapping is caused by symmetry-induced suppression of radiative recombination.

Behavior can be observed using near-field optical microscopy.

Abstract

We theoretically analyze the carrier capture and distribution among the available energy levels of a symmetric semiconductor quantum dot under continuous-wave excitation resonant with the barrier energy levels. At low temperature all the dot level-occupations but one decrease monotonically with energy. The uncovered exception, corresponding to the second (dark) energy level, displays a steady-state carrier density exceeding that of the lowest level more than a factor two. The root cause is not radiative recombination before relaxation to lower energy levels, but at the opposite, carrier trapping due to the symmetry-induced suppression of radiative recombination. Such a behaviour can be observed by collection-mode near-field optical microscopy.