  Restoring force acts on the electronic cloud of the outer electrons of a
neutral or charged impurity atom when it is shifted relative to the inner
charged core. Because of this the dipole oscillation arises, which influences
considerably the dispersion law of the plasma oscillation in bulk donor
semiconductors. Assuming that only one transition of the outer electron from
the ground state to the first excited state is essential, the dispersion law is
calculated. It is shown that calculated dispersion law consists of two separate
branches, one of them originates from the regular plasma oscillation of the
free electrons of a conductivity band, and the other one stems from the local
oscillation of the outer electrons bounded to the impurity atoms.
