Kavli Affiliate: Giordano Scappucci
| First 5 Authors: Stefano Achilli, Damiano Marian, Mario Lodari, Emiliano Bonera, Giordano Scappucci
| Summary:
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.
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