Optical spin orientation of minority holes in a modulation-doped GaAs/(Ga,Al)As quantum well

TL;DR

This paper investigates the optical spin orientation of minority holes in a GaAs/(Ga,Al)As quantum well, revealing how magnetic fields influence spin polarization and relaxation mechanisms in a high-mobility 2D electron gas system.

Contribution

It demonstrates that spin-polarized minority holes are responsible for optical spin orientation effects and models their behavior considering Landau levels and hole subband mixing.

Findings

Spin polarization influenced by magnetic fields can be explained by Landau level absorption and subband mixing.

Hole spin relaxation is governed by the Dyakonov-Perel' mechanism and slowed by the Ivchenko mechanism.

Hole mobility is significantly lower than electron mobility due to scattering with the electron gas.

Abstract

The optical spin orientation effect in a GaAs/(Ga,Al)As quantum well containing a high-mobility 2D electron gas was found to be due to spin-polarized minority carriers, the holes. The observed oscillations of both the intensity and polarization of the photoluminescence in a magnetic field are well described in a model whose main elements are resonant absorption of the exciting light by the Landau levels and mixing of the heavy- and light-hole subbands. After subtraction of these effects, the observed influence of magnetic fields on the spin polarization can be well interpreted by a standard approach of the optical orientation method. The spin relaxation of holes is controlled by the Dyakonov-Perel' mechanism. Deceleration of the spin relaxation by the magnetic field occurs through the Ivchenko mechanism - due to the cyclotron motion of holes. Mobility of holes was found to be two orders of magnitude smaller than that of electrons, being determined by the scattering of holes upon the electron gas.