Optical Orientation of Excitons in CdSe Self-Assembled Quantum Dots

TL;DR

This study investigates exciton spin dynamics in CdSe quantum dots using optical orientation and magnetic fields, revealing how polarization and relaxation times vary with temperature and magnetic field.

Contribution

It provides new insights into exciton spin relaxation times and their dependence on magnetic field and temperature in self-assembled CdSe quantum dots.

Findings

Exciton polarization increases with magnetic field.

Spin relaxation times are 100 ps without field and 2.2 ns with field.

Temperature decreases polarization independently of magnetic field.

Abstract

We study spin dynamics of excitons confined in self-assembled CdSe quantum dots by means of optical orientation in magnetic field. At zero field the exciton emission from QDs populated via LO phonon-assisted absorption shows a circular polarization of 14%. The polarization degree of the excitonic emission increases dramatically when a magnetic field is applied. Using a simple model, we extract the exciton spin relaxation times of 100 ps and 2.2 ns in the absence and presence of magnetic field, respectively. With increasing temperature the polarization of the QD emission gradually decreases. Remarkably, the activation energy which describes this decay is independent of the external magnetic field, and, therefore, of the degeneracy of the exciton levels in QDs. This observation implies that the temperature-induced enhancement of the exciton spin relaxation is insensitive to the energy level degeneracy and can be attributed to the same excited state distribution.