Bloch transport of electrons and holes in superlattice minibands: Direct measurement by subpicosecond luminescence spectroscopy

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Abstract
The perpendicular transport of photoexcited electrons and holes in graded-gap GaAs-AlGaAs superlattices is directly determined by subpicosecond luminescence spectroscopy. We show that the electron and and hole transport is through extended, Bloch-type states for superlattice periods ̊, and determine the mobility for such transport. Increasing the superlattice period to 60 Å reduces the mobility by a factor of 20, resulting from an order of magnitude reduction in the hole miniband width. Our results also provide the first evidence of diffusion enhanced by potential steps.