10 research outputs found
Doppler velocimetry of spin propagation in a two-dimensional electron gas
Controlling the flow of electrons by manipulation of their spin is a key to
the development of spin-based electronics. While recent demonstrations of
electrical-gate control in spin-transistor configurations show great promise,
operation at room temperature remains elusive. Further progress requires a
deeper understanding of the propagation of spin polarization, particularly in
the high mobility semiconductors used for devices. Here we report the
application of Doppler velocimetry to resolve the motion of spin-polarized
electrons in GaAs quantum wells driven by a drifting Fermi sea. We find that
the spin mobility tracks the high electron mobility precisely as a function of
T. However, we also observe that the coherent precession of spins driven by
spin-orbit interaction, which is essential for the operation of a broad class
of spin logic devices, breaks down at temperatures above 150 K for reasons that
are not understood theoretically
Spin- and energy relaxation of hot electrons at GaAs surfaces
The mechanisms for spin relaxation in semiconductors are reviewed, and the
mechanism prevalent in p-doped semiconductors, namely spin relaxation due to
the electron-hole exchange interaction, is presented in some depth. It is shown
that the solution of Boltzmann-type kinetic equations allows one to obtain
quantitative results for spin relaxation in semiconductors that go beyond the
original Bir-Aronov-Pikus relaxation-rate approximation. Experimental results
using surface sensitive two-photon photoemission techniques show that the spin
relaxation-time of electrons in p-doped GaAs at a semiconductor/metal surface
is several times longer than the corresponding bulk spin relaxation-times. A
theoretical explanation of these results in terms of the reduced density of
holes in the band-bending region at the surface is presented.Comment: 33 pages, 12 figures; earlier submission replaced by corrected and
expanded version; eps figures now included in the tex
Spin-injection Hall effect in a planar photovoltaic cell
Successful incorporation of the spin degree of freedom in semiconductor
technology requires the development of a new paradigm allowing for a scalable,
non-destructive electrical detection of the spin-polarization of injected
charge carriers as they propagate along the semiconducting channel. In this
paper we report the observation of a spin-injection Hall effect (SIHE) which
exploits the quantum-relativistic nature of spin-charge transport and which
meets all these key requirements on the spin detection. The two-dimensional
electron-hole gas photo-voltaic cell we designed to observe the SIHE allows us
to develop a quantitative microscopic theory of the phenomenon and to
demonstrate its direct application in optoelectronics. We report an
experimental realization of a non-magnetic spin-photovoltaic effect via the
SIHE, rendering our device an electrical polarimeter which directly converts
the degree of circular polarization of light to a voltage signal.Comment: 14 pages, 4 figure