Theory of intrinsic spin-dependent transport in semiconductors and two-dimensional membranes

Thesis (Ph. D.)--University of Rochester. Dept. of Physics and Astronomy, 2013. Chapters 2-5 based in whole or part on various research papers "in collaboration with Prof. Hanan Dery [...] developed through a continuous exchange of ideas between both authors for the physics and writing of the paper[s]"--P. ix-x. "The work on germanium in Chapter 4 is from a research paper [...] in collaboration with Pengke Li and Prof. Hanan Dery, where Pengke Li and [Yang Song] contributed equally to this work"--P. x.A reliable theoretical framework is developed for spin-dependent transport in the presence of electron-phonon interactions. The centerpiece of the theory explores the symmetry of the studied systems and processes. In addition, microscopic kinetic processes are incorporated. Rigorous numerical methods are employed in order to verify our predictions. Applying the theory to potential key semiconductors for spintronics, such as silicon and germanium, and to the nascent material family of two-dimensional membranes, one obtains physical clarity as well as explicit analytical results. Following the construction of electronic and phonon states, we derive spin-dependent electronphonon scattering matrix elements for all processes induced by acoustic or optical phonons (including transparent derivations of important two-phonon processes in two-dimensional membranes), intravalley or intervalley scattering for multivalley conduction bands, and interband scattering for the gapless graphene. The resulting expressions are explicit functions of electron wavevectors, spin orientation, phonon modes and valley positions. Using the acquired insights, remarkable physical consequences are discovered. These include optimal spin transport in Si by combining strain and geometrical constrains, extremely long room-temperature spin lifetime in strained Ge when the spin is oriented parallel to a [111] strain (∼1 μs), and ultrafast electron spin relaxation in single-layer transition-metal dichalcogenides. By the unique properties of two-dimensional membranes inherited from their mirror symmetry and out-of-plane softness, we notice decoupling between spin and momentum transport due to scattering with out-of-plane acoustic phonons (the most populous branch). By symmetry analysis of orbital configurations, contrasting spin splitting and spin flip constants are predicted for the conduction bands of various single-layer transition-metal dichalcogenides. In addition to transport phenomena, we also apply the theory to optical excitation of hot excitons. Incorporating microscopic spin-flip results into Boltzmann transport equations, one can explore spin communication applications. Apart from spin relaxation, spin injection and detection are also key phases. We study tunnel-barrier profiles that are complicated by doping inhomogeneity, and quantify the limitations on the applied bias due to detrimental spin relaxation of hot electrons in zinc-blende semiconductors. Importantly, we elaborate dynamic signals of high-frequency devices, and noncollinear magnetization configurations of the electrodes to discuss optimal information density