OPTICAL-DETECTION OF VERTICAL TRANSPORT IN SHORT-PERIOD GAAS/ALGAAS SUPERLATTICES

In short-period superlattices carriers are able to move perpendicularly to the layers. Optical experiments are convenient tools to observe this transport, called vertical transport, and to determine its variations with the superlattice period and the structural disorder. Electron and hole transports are differentiated using appropriate excitation densities, and their diffusion coefficients are estimated. In agreement with the miniband width calculations, the transition from a Bloch conduction to a hopping conduction is observed at different values of the superlattice period for electrons and holes. Finally, vertical transport must be taken into account to understand the differences between absorption and excitation spectra in superlattices; AlGaAs cladding layers are necessary to avoid the escape of carriers into the substrate.