  We investigate the phonon mechanism for the orientational pinning of Wigner
crystals and stripes in two-dimensional electron layers in GaAs matrices. We
find the orientation of bilayer Wigner crystals on the (001), (111), (0-11) and
(311) interfaces versus the interlayer distance and determine the regions of
parameters, where polydomain structures can emerge. For the stripe states in
electron layers situated close to the (001) surface we show that the
interference between the piezoelectric and deformation potential interaction
may be responsible for the preferable orientation of the stripes along the
[110] direction. For the bilayer system on the (001) interfaces we predict the
suppression of the resistance anisotropy.
