Polarization of Luminescence in the Nanostructure Si/CaF2 Upon Polarization of the Nuclear Spins of Fluorine

Abstract

The laws governing polarization of luminescence in the nanostructure Si/CaF 2 upon polarization of the spins of the fluorine nuclei by means of optical excitation of charge carriers are considered theoretically. The possibility of studying experimentally the properties of nuclear spins in analyzing luminescence is shown. The polarization of luminescence is most informative in the range of excitation rates of charge carriers from 3⋅10 7 to 3⋅10 8 sec −1 with the CaF 2 layer of thickness from 0.6 to 0.8 nm and optical excitation polarization degree of 0.1. Introduction.Experimental study of the laws governing polarization and relaxation of nuclear spins in lowdimensional structures on excitation of an electronic subsystem is a particularly urgent problem for nano-and optoelectronics, spintronics, memory on nuclear spins, and quantum computations [1,2]. For these purposes, it is advisable to use methods of optical detection that involve the spectroscopy of spin-polarized electron transitions in low-dimensional structures. Among the most informative methods is the method of polarized luminescence in which the magnitude of recombination radiation polarization in a magnetic field perpendicular to the direction of nuclear magnetization is measured [3].Polarization of the nuclear spins of fluorine in volumetric samples of CaF 2 containing paramagnetic impurities is usually conducted by saturating hyperfine interaction between paramagnetic centers (U 3+ , Mn 2+ , Ce 3+ ) and the 19 F nuclei by a radio-frequency field [4][5][6]. The use of spin-polarized charge carriers [3] to polarize fluorine nuclei in volumetric samples is, however, not very effective since CaF 2 is a dielectric. To overcome this shortcoming, we suggested in [2] to use periodic nanostructures Si/CaF 2 that provide a fundamentally new possibility of polarizing the nuclear spins of fluorine due to interaction with a spin-polarized electronic subsystem. Alteration of nano-sized layers of Si and CaF 2 makes it possible to use optical or injection excitation in order to obtain in silicon a significant number of nonequilibrium spin-polarized charge carriers that, while interacting with fluorine in the neighboring regions of CaF 2 , ensure spin polarization of the nuclei of the latter.At the same time, typical of the Si/CaF 2 structure is luminescence (at a wavelength from 560 to 580 nm) because of the presence of a direct-band transition in nano-sized silicon [7,8]; this luminescence makes it possible to carry out spectroscopic investigations of spin-polarized electron transitions in it. However, informative experimental study of luminescence polarization is possible only if there is a model describing polarization of recombination radiation in the Si/CaF 2 structure.The aim of the present work is a theoretical analysis of luminescence polarization in the periodic nano-sized Si/CaF 2 structure which is associated with polarization of the nuclear spins of fluorine via optical excitation of electron transitions. It is assumed that this structure lacks magnetic ...