  A detailed study of the circular photogalvanic effect (CPGE) in SiGe
structures is presented. It is shown that the CPGE becomes possible due to the
built-in asymmetry of quantum wells (QWs) in compositionally stepped samples
and in asymmetrically doped structures. The photocurrent arises due to optical
spin orientation of free carriers in QWs with spin splitting in k-space. It is
shown that the effect can be applied to probe the macroscopic in-plane symmetry
of low dimensional structures and allowing to conclude on Rashba or Dresselhaus
terms in the Hamiltonian.
