Electrical control of optical orientation of neutral and negatively charged excitons in n-type semiconductor quantum well

TL;DR

This study demonstrates a significant electric field effect on the spin polarization of excitons and trions in n-type GaAs/AlGaAs quantum wells, revealing a polarization sensitivity of 200% per Volt due to exciton trapping by quantum dots.

Contribution

It introduces a novel electric control method for optical orientation of excitons and trions in quantum wells, highlighting the role of interfacial fluctuations in spin polarization enhancement.

Findings

Electric field induces a giant increase in exciton spin polarization.

Polarization sensitivity reaches 200% per Volt.

Efficient trapping of neutral excitons by quantum dots enhances polarization.

Abstract

We report a giant electric field induced increase of spin orientation of excitons in n-type GaAs/AlGaAs quantum well. It correlates strongly with the formation of negatively charged excitons (trions) in the photoluminescence spectra. Under resonant excitation of neutral heavy-hole excitons, the polarization of excitons and trions increases dramatically with electrical injection of electrons within the narrow exciton-trion bias transition in the PL spectra, implying a polarization sensitivity of 200 % per Volt. This effect results from a very efficient trapping of neutral excitons by the quantum well interfacial fluctuations (so-called "natural" quantum dots) containing resident electrons.