Optical studies of electric field domains in GaAs-AlxGa1−xAs superlattices

The spatial distribution of an electric field parallel to the growth axis in undoped GaAs-${\mathrm{Al}}_{\mathrm{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As superlattices under optical excitation is investigated by photocurrent-voltage measurements and photoluminescence (PL) spectroscopy. At low excitation densities the applied electric field is uniform throughout the superlattice. At high excitation densities the electric field breaks up into regions of different field strengths, electric field domains. These field strengths are directly related to the conduction-subband spacings in the superlattice. The spatial distribution, i.e., the location of the different domains along the growth axis, is determined by measuring the PL spectrum at different excitation wavelengths. The space charge located at the domain boundaries is shown to be electrons.