6 research outputs found
Bipolar spintronics: From spin injection to spin-controlled logic
An impressive success of spintronic applications has been typically realized
in metal-based structures which utilize magnetoresistive effects for
substantial improvements in the performance of computer hard drives and
magnetic random access memories. Correspondingly, the theoretical understanding
of spin-polarized transport is usually limited to a metallic regime in a linear
response, which, while providing a good description for data storage and
magnetic memory devices, is not sufficient for signal processing and digital
logic. In contrast, much less is known about possible applications of
semiconductor-based spintronics and spin-polarized transport in related
structures which could utilize strong intrinsic nonlinearities in
current-voltage characteristics to implement spin-based logic. Here we discuss
the challenges for realizing a particular class of structures in semiconductor
spintronics: our proposal for bipolar spintronic devices in which carriers of
both polarities (electrons and holes) contribute to spin-charge coupling. We
formulate the theoretical framework for bipolar spin-polarized transport, and
describe several novel effects in two- and three-terminal structures which
arise from the interplay between nonequilibrium spin and equilibrium
magnetization.Comment: 16 pages, 7 figure
Semiconductor Spintronics
Spintronics refers commonly to phenomena in which the spin of electrons in a
solid state environment plays the determining role. In a more narrow sense
spintronics is an emerging research field of electronics: spintronics devices
are based on a spin control of electronics, or on an electrical and optical
control of spin or magnetism. This review presents selected themes of
semiconductor spintronics, introducing important concepts in spin transport,
spin injection, Silsbee-Johnson spin-charge coupling, and spindependent
tunneling, as well as spin relaxation and spin dynamics. The most fundamental
spin-dependent nteraction in nonmagnetic semiconductors is spin-orbit coupling.
Depending on the crystal symmetries of the material, as well as on the
structural properties of semiconductor based heterostructures, the spin-orbit
coupling takes on different functional forms, giving a nice playground of
effective spin-orbit Hamiltonians. The effective Hamiltonians for the most
relevant classes of materials and heterostructures are derived here from
realistic electronic band structure descriptions. Most semiconductor device
systems are still theoretical concepts, waiting for experimental
demonstrations. A review of selected proposed, and a few demonstrated devices
is presented, with detailed description of two important classes: magnetic
resonant tunnel structures and bipolar magnetic diodes and transistors. In most
cases the presentation is of tutorial style, introducing the essential
theoretical formalism at an accessible level, with case-study-like
illustrations of actual experimental results, as well as with brief reviews of
relevant recent achievements in the field.Comment: tutorial review; 342 pages, 132 figure
Demonstration of the spin solar cell and spin photodiode effect
Spin injection and extraction are at the core of semiconductor spintronics. Electrical injection is one method of choice for the creation of a sizeable spin polarization in a semiconductor, requiring especially tailored tunnel or Schottky barriers. Alternatively, optical orientation can be used to generate spins in semiconductors with significant spin-orbit interaction, if optical selection rules are obeyed, typically by using circularly polarized light at a well-defined wavelength. Here we introduce a novel concept for spin injection/extraction that combines the principle of a solar cell with the creation of spin accumulation. We demonstrate that efficient optical spin injection can be achieved with unpolarized light by illuminating a p-n junction where the p-type region consists of a ferromagnet. The discovered mechanism opens the window for the optical generation of a sizeable spin accumulation also in semiconductors without direct band gap such as Si or Ge
Cross-sectional imaging of spin injection into a semiconductor
Recent discoveries of phenomena that relate electronic transport in solids to the spin angular momentum of the electrons are the fundamentals of spin electronics (spintronics). The first proposed conceptual spintronic device, the spin field-effect transistor—which has not yet been successfully implemented—requires the creation and detection of spin-polarized currents in a semiconductor. Whereas electrical spin injection from a ferromagnetic metal into GaAs has been achieved recently, the detection techniques used up to now have drawbacks like the requirement of large magnetic fields or limited information about the spin polarization in the semiconductor. Here we introduce a method that, by observation across a cleaved edge, enables us to directly visualize fully remanent electrical spin injection into bulk GaAs from a ferromagnetic contact, to image the spin-density distribution in the semiconductor in a cross-sectional view and to separate the effects of spin diffusion and electron drift