Photoluminescence of double quantum wells: asymmetry and excitation laser wavelength effects

TL;DR

This study investigates how excitation wavelength and structural asymmetry in double quantum wells influence electron spin lifetime, revealing that longer wavelengths and asymmetry increase spin retention by reducing relaxation mechanisms.

Contribution

It provides new insights into how excitation wavelength and quantum well asymmetry affect electron spin lifetime in GaAs/AlGaAs double quantum wells.

Findings

Longer excitation wavelengths increase spin lifetime.

Asymmetric quantum wells exhibit higher spin lifetimes.

Rashba and Dresselhaus mechanisms influence spin relaxation.

Abstract

Circularly polarized photoluminescence (PL) spectroscopy measured at 19 K on GaAs/AlGaAs symmetric and asymmetric double quantum wells (DQW) is reported. The PL is obtained by exciting the sample with a circularly polarized (left or right) laser in order to create an initial unbalanced distribution of electron spins in the conduction band and, in this way, obtain the electron spin lifetime $\tau_s$. The effects of the excitation laser wavelength were estimated by exciting with laser wavelengths of 701.0 nm, 787.0 nm, 801.5 nm and 806.5 nm. The increase of $\tau_s$ with the excitation wavelength is attributed to the lower initial quasi-momentum $\bf{k}$ of the excited carriers, which also reduces spin-orbit relaxation processes. $\tau_s$ was found to be higher in asymmetric DQWs: this is attributed to the wider QWs in these samples, which reduces spin relaxation due to the Dresselhaus mechanism. In addition, we also detected a smaller contribution from the Rashba mechanism by comparing samples with built-in electric fields of different orientations defined by doped barrier layers.