Etude du pompage optique du silicium par photoluminescence polarisée et photo-émission à basse énergie résolue en spin

Abstract : Optical pumping techniques are usually well adapted for the study of spin dynamics in semiconductors. Silicon is a special case, because of an indirect bandgap and a low spin-orbit coupling.
Our approach consists in «reducing the lifetime» of conduction electrons, so that their initial polarization is preserved.
First, we carried out a polarized photoluminescence. Reducing lifetime is achieved mainly by varying the acceptor concentration. A highly polarized hot luminescence is evidenced on a heavyly doped sample. However, the depolarization effect of a transverse field is not observed.
Secondly, we carried out a spin- and energy-resolved photoemission experiment, for a range of excitation energy going from the infrared up to the ultraviolet. The relevant scale of time is the escape time, which is much shorter than the lifetime. It involved the activation of silicon photocathodes in a negative electronic affinity. We performed a spectroscopic study of the photoemited electronic distributions with a 20 meV resolution. The spin analysis of these distributions showed a dramatic increase of the electronic polarization as the excitation energy is approaching the direct bandgap. Polarizations as high as 15% are measured, in agreement with our theoretical calculations. We also observed a change of sign of the polarization, which is very sensitive to the temperature, in the thermalized part of the electronic distributions.
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Submitted on : Thursday, March 26, 2009 - 3:59:54 PM
Last modification on : Wednesday, March 27, 2019 - 4:18:02 PM
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Frédéric Roux. Etude du pompage optique du silicium par photoluminescence polarisée et photo-émission à basse énergie résolue en spin. Physique [physics]. Ecole Polytechnique X, 2008. Français. ⟨tel-00371155⟩

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