Inter-valley scattering and electric field domains in quantum well infrared photodetectors

We report on the formation of electric field domains induced by the bound-to-continuum photocurrent in n-type GaAs/AlGaAs multiple quantum wells. Domain formation is caused by a negative differential photoconductivity, which arises from inter-valley scattering processes. The domain structure is only observed under illumination, since the thermally excited carrier density increases strongly with increasing electric field, while the optical excitation rate remains constant. The signature of electric field domains, i. e., a plateau-like behavior of the total current under illumination, Is most clearly seen If the interference of the infrared illumination is suppressed by using devices which are only partially covered with metal.