Optical pumping in Silicon thin films

Abstract : Silicon is a potentially promising material for spintronics due to its long spin relaxation time. At the same time, classical approaches to the study of the conduction electrons' polarization, such as luminescence, are ineffective for Silicon due to the weak spin-orbit interaction and indirect-bandgap structure. In the present work, the polarization of the conduction electrons is studied by means of spin-resolved low-energy electron photoemission spectroscopy. The Silicon surface is activated to negative electron affinity by Cesium and Oxygen adsorption so that electron emission can be achieved with photon excitation very close to the band gap (1.12eV at 300K). We use a tunable laser which allows a systematic measurement of the polarization spectra from the absorption onset up to energies above the Gamma2- band. We measured spin polarization spectra on Silicon-on-insulator films of different thicknesses. Based on the obtained data, band structure parameters such as direct band gap and the spin-orbit splitting are evaluated. However, contrary to expectations, when diminishing the Silicon film thickness, even below the value of the spin diffusion length, the electron polarization remains close to zero (-0.4%), much lower than the theoretically predicted values of the initial polarization (-20%), thus bringing into question their straightforward interpretation. A theoretical investigation was performed on the basis of an ab initio band structure model in order to calculate the full spin polarization spectra. These calculations are still on-going but predictions for strained Silicon confirm that this material should be an interesting candidate for further spin polarization studies.
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Contributor : Igor Favorskiy <>
Submitted on : Monday, February 24, 2014 - 1:43:52 AM
Last modification on : Wednesday, March 27, 2019 - 4:18:02 PM

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  • HAL Id : pastel-00950979, version 1

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Igor Favorskiy. Optical pumping in Silicon thin films. Materials Science [cond-mat.mtrl-sci]. Ecole Polytechnique X, 2013. English. ⟨pastel-00950979⟩

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