Theory of quantum dot spin-lasers

TL;DR

This paper develops a theoretical model for quantum dot spin-lasers, highlighting how spin-polarized injection influences laser thresholds, polarization, and emission saturation, with implications for improving spin-laser performance.

Contribution

It introduces an analytical rate-equations model for quantum dot spin-lasers, accounting for wetting layer effects and demonstrating preserved advantages of spin injection.

Findings

Spin injection reduces lasing thresholds.

Wetting layer impacts carrier capture and emission saturation.

Spin-filtering effect persists despite saturation effects.

Abstract

We formulate a model of a semiconductor Quantum Dot laser with injection of spin-polarized electrons. As compared to higher-dimensionality structures, the Quantum-Dot-based active region is known to improve laser properties, including the spin-related ones. The wetting layer, from which carriers are captured into the active region, acts as an intermediate level that strongly influences the lasing operation. The finite capture rate leads to an increase of lasing thresholds, and to saturation of emitted light at higher injection. In spite of these issues, the advantageous threshold reduction, resulting from spin injection, can be preserved. The "spin-filtering" effect, i.e., circularly polarized emission at even modest spin-polarization of injection, remains present as well. Our rate-equations description allows to obtain analytical results and provides transparent guidance for improvement of spin-lasers.