  The electron spin dynamics is studied by time-resolved Kerr rotation in
GaAs/AlGaAs quantum wells embedded in a negatively doped-intrinsic-positively
doped structures grown on (111)A or (111)B-oriented substrates. In both cases
the spin lifetimes are significantly increased by applying an external electric
field but this field has to point along the growth direction for structures
grown on (111)A and opposite to it for the ones grown on (111)B. This extended
electron spin lifetime is the result of the suppression of the D'yakonov-Perel
spin relaxation mechanism [Sov. Phys. Solid State 13, 3023 (1972)] due to the
cancellation effect of the internal Dresselhaus term [Phys. Rev. 100, 580
(1955)] with the external electric field induced Rashba one [J. Phys. C 17,
6039 (1984)], both governing the conduction band spin-orbit splitting. These
results demonstrate the key role played by the growth direction in the design
of spintronic devices.
