  A contribution of the electron-phonon interaction into the energy of a
unidirectional charge ordered state (stripe phase) of two-dimensional electrons
in GaAs heterostructures is analyzed. The dependence of the energy on the
direction of the electron density modulation is calculated. It is shown that in
electrons layers situated close to the (001) surface the interference between
the piezoelectric and the deformation potential interaction causes a
preferential orientation of the stripes along the [110] axis.
