Spintronics is an emerging new field of electronics that proposes to use
instead of charge for information processing. A crucial part of spintronic
devices is the electrical injection of spin polarized electrons from
ferromagnetic contacts into semiconductor structures. Recently, it has been
shown that efficient spin injection is possible from Fe into GaAs by
tunneling through a reverse-biased Schottky contact.
In this presentation, the influence of the chemical, electronic, and
interface structure on spin transport across the interface will be
with particular focus on the Fe/GaAs system. The magnetic properties of the
Fe/GaAs interface have previously been studied and discussed in terms of
formation of a "magnetically-dead layer" at the interface due to Fe/GaAs
reactions. I will show that the effect of interface formation on spin
transport is more complex than this simple model and a remarkable wealth of
spin injecting interfaces with different properties is found.
Optimized Fe/(Al,Ga)As heterostructures show an injected steady-state
electron spin polarization of ~40% at 2K. Assuming the spin polarization of
bulk Fe of 42%, this would correspond to near unity spin injection
efficiency. The temperature and bias dependence of spin injection is
discussed in terms of spin relaxation in GaAs quantum wells and bulk GaAs.
Room temperature spin injection of at least 8% is demonstrated.
Also, first results of the imaging of spin transport in lateral
heterostructures will be shown and spin drift after electrical spin
over tens of microns in a semiconductor device will be demonstrated. It is
also shown that electrical detection of optically injected spin is possible
using Fe/GaAs Schottky contacts. This path will ultimately lead to
all-electric semiconductor spintronic devices.