  We present the analytical result of the expectation value of spin resulting
from an injected spin polarized electron into a semi-infinitely extended 2DEG
plane with [001] growth geometry via ideal quantum point contact. Both the
Rashba and Dresselhaus spin-orbit couplings are taken into account. A pictorial
interpretation of the spin precession along certain transport directions is
given. The spin precession due to the Rashba term is found to be especially
interesting since it behaves simply like a windshield wiper which is very
different from the ordinary precession while that due to the Dresselhaus term
is shown to be crystallographic-direction-dependent. Some crystallographic
directions with interesting and handleable behavior of spin precession are
found and may imply certain applicability in spintronic devices.
