Optical spin pumping in silicon

TL;DR

This paper introduces an all-optical spin pumping method in silicon using a Ge-on-Si heterostructure, achieving high polarization of emitted light and overcoming previous limitations in silicon's optical spin manipulation.

Contribution

The study presents a novel all-optical approach for spin injection in silicon, enabling high polarization emission and expanding silicon's potential in spintronics and quantum technologies.

Findings

Achieved up to 9% polarization degree in silicon luminescence.

Demonstrated spin injection facilitated by carrier lifetime shortening.

Validated the method using magneto-optic experiments.

Abstract

The generation of an out-of-equilibrium population of spin-polarized carriers is a keystone process for quantum technologies and spintronics alike. It can be achieved through the so-called optical spin orientation by exciting the material with circularly polarized light. Although this is an established technique for studying direct band-gap semiconductors, it has been proven limited in materials like Si that possess weak oscillator strengths for the optical transitions. In this study, we address the problem by presenting an all-optical analog of the spin pumping method. This involves the optical creation of a non-equilibrium spin population within an absorber, which subsequently transfers spin-polarized carriers to a nearby indirect gap semiconductor, resulting in polarized emission from the latter. By applying this concept to a Ge-on-Si heterostructure we observe luminescence from Si with an unrivaled polarization degree as high as 9%. The progressive etching of the absorbing layer, assisted by magneto-optic experiments, allows us to ascertain that the polarized emission is determined by effective spin injection aided by the carrier lifetime shortening due to extended defects. These findings can facilitate the use of highly promising spin-dependent phenomena of Si, whose optical exploitation has thus far been hampered by fundamental limitations associated with its peculiar electronic structure.