Institut für Theoretische Physik, Universität, D-93040 Regensburg, Germany
The spin degree of freedom of charge carriers has
recently found increasing attention in the perspective of spin or magneto
electronics . The operation of a spin transistor or of a spin-valve
device depends essentially on the lifetime of a spin-polarized electron
(or hole). Taking the spin transistor  as paradigm spin relaxation is
related to the faith of carriers travelling along the conducting channel
at a semiconductor heterointerface. As known from extensive studies for
bulk semiconductors  all mechanisms of spin relaxation can be traced
back to spin-orbit interaction, which comes into play in different ways:
In semiconductor systems with reduced dimension spin relaxation is modified due to confinement  and interface effects  and depends on the material parameters of the system with the tendency, that the relaxation rates increase with a decrease of the gap energy.
The dependence of the spin precession (Dyakonov-Perel mechanism) on the crystallographic orientation of the heterointerface (or quantum well) allows to discriminate between different spin relaxation mechanisms .
The talk gives a survey on the mechanisms of spin
relaxation in bulk material and on their modification due to reduced dimensionality
in semiconductor heterostructures.