Excited states of neutral and charged excitons in single strongly asymmetric InP-based nanostructures emitting in the telecom C band

TL;DR

This study explores the excited states of neutral and charged excitons in highly asymmetric InP nanostructures emitting in the telecom C band, combining experimental microphotoluminescence excitation measurements with theoretical calculations.

Contribution

It provides direct observation and identification of exciton excited states and their optical properties in asymmetric nanostructures, advancing understanding of their quantum confinement effects.

Findings

Successfully probed absorption spectra of exciton states

Identified optical transitions involving excited carrier levels

Observed conserved spin configuration during exciton relaxation

Abstract

We investigate strongly asymmetric self-assembled nanostructures with one of dimensions reaching hundreds of nanometers. Close to the nanowire-like type of confinement, such objects are sometimes assigned as one-dimensional in nature. Here, we directly observe the spectrum of exciton excited states corresponding to longitudinal quantization. This is based on probing the optical transitions via polarization-resolved microphotoluminescence excitation ($\mu$PLE) measurement performed on single nanostructures combined with theoretical calculation of neutral and charged exciton optical properties. We successfully probe absorption-like spectra for individual bright states forming the exciton ground-state fine structure, as well as for the negatively charged exciton. Confronting the calculated spectrum of excitonic absorption with $\mu$PLE traces, we identify optical transitions involving states that contain carriers at various excited levels related to the longest dimension. Based on cross-polarized excitation-detection scheme, we show very well conserved spin configuration during orbital relaxation of the exciton from a number of excited states comparable to the quasi-resonant pumping via the optical phonon, and no polarization memory for the trion, as theoretically expected.