Nonlinear photogalvanic effect induced by monopolar spin orientation of holes in QWs

We report on the first observation of the circular photogalvanic effect (CPGE) induced by optical monopolar spin orientation of holes in p-doped quantum-well structures. It is shown that monopolar optical spin orientation of free carriers causes an electric current which reverses its direction upon changing from left to right circularly polarized radiation. The effect has been observed in (001)- and (311)A-oriented p-GaAs/AlGaAs quantum wells at normal incidence of far-infrared radiation. The photocurrent is proportional to the light intensity at low power levels and gradually saturates with increasing intensity. The CPGE can be utilized to investigate separately spin polarization of electrons and holes and to determine spin-relaxation times.