Photogalvanic currents in quantum well structures induced by infrared radiation

Abstract

A circular photogalvanic effect and a magnetic field induced circular photogalvanic effects caused by absorption of far infrared radiation have been observed in quantum well (QW) structures. Applying circularly polarized infrared radiation a monopolar spin polarization has been achieved. The spin polarization results in a directed motion of free carriers in the plane of a quantum well. The coupling of the helicity of the incoming photons to spin polarized final states with net momentum is caused by angular momentum selection rules together with band splitting in k-space due to k-linear terms in the Hamiltonian. These spin photocurrents have been observed in GaAs, InAs, and Si/Ge QW structures for a wide temperature range from room to liquid helium temperature by using a pulsed far-infrard molecular laser delivering 100 ns pulses at wavelengths from 9 µm to 280 µm. The conversion of spin orientation of carriers into directed motion provides efficient methods to determine spin relaxation times of electrons in n-type materials and of holes in p-type materials.