Transition between coherent and incoherent electron transport in GaAs/GaAlAs superlattices

The transition between coherent and incoherent transport in undoped GaAs/AlGaAs superlattices is observed. Hot electron spectroscopy is used to measure the superlattice transmittance at different bias conditions. For a short-period superlattice the transmittance is found to be independent of the direction of the electric field. For a superlattice larger than the coherence length, the transmission becomes asymmetric and dependent on the electric field direction. The onset of scattering-induced miniband transport is clearly evident. A coherence length of 150 nm, limited by surface roughness, and a scattering time of 1 ps are determined.