Abstract

The spin degree of freedom attracts the attention of many researchers, because the electron spin offers two distinguishable states with spin up and down along a chosen axis in a good analogy to the two states of a digital bit. Although the idea of spin-based logic was already formulated in the 60ies of the last century, however, it has not been realized until recently, when electrical and optical spin manipulation without any need of a magnetic field was introduced. Nowadays, spin electronics - spintronics - is a rapidly developing research and development area which offers novel devices with characteristics not only comparable but even superior to those of the state-of-the-art charge-based devices.

In order to build a spin-based device the spin transport properties in semiconducting materials must be closely examined. Because silicon is the most widely used material of modern microelectronics, the details of spin relaxation in silicon channels are of paramount interest. Also, strain is routinely used to achieve a charge carrier mobility enhancement in modern MOSFETs. In this thesis the k⋅p method is used to examine the subband structure and the wave functions in confined electron systems of silicon films in the presence of shear strain and spin-orbit coupling. Analytical expressions for the four-band k⋅p Hamiltonian are found in case of a square well potential. The wave functions are used to evaluate the corresponding spin relaxation matrix elements. The analysis of the spin lifetime comprises contributions from surface roughness and electron-phonon mediated spin relaxation. Because the unprimed subband degeneracy is lifted by shear strain, thus suppressing the most important elastic intervalley contribution to spin relaxation, the spin lifetime enhancement by an order of magnitude in strained silicon films is predicted.

Utilizing silicon in spin-based field-effect transistors (SpinFETs) is of a great interest, since it promises to build spin devices using the well developed silicon processing. Due to the interface induced inversion symmetry breaking the strength of the electric field dependent spin-orbit interaction is enhanced in thin silicon films and fins. It is shown that in case of properly designed Schottky barriers between the source/drain and the channel a pronounced modulation of the channel magnetoresistance persists at room temperature. In order to reduce the channel length, the transport mass along the channel must be large. Based on the two-band k⋅p model for the conduction band, a stronger dependence on the value of the effective spin-orbit interaction in silicon SpinFETs with a [100]-oriented silicon fins is predicted, making them preferable for practical realization.

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