We apply intersubband electroabsorption spectroscopy to a current-carrying multiple quantum-well structure device, in order to simultaneously measure the steady state carrier density and the average time carriers spend in each quantum well. By comparing our measurements with a simple quantum mechanical tunneling model, we show directly that electrons sequentially tunnel through the periodic quantum structure. In addition, we use photoinduced absorption spectroscopy to measure the effect of the applied electric field on electron states within the minibands in the energy continuum. We show that already at relatively small fields, the optical transitions into the continuum minibands merge into a single spectral band. Using an eight-band model, we explain this observation in terms of field-induced miniband state localization.

• Received 20 May 1999

DOI:https://doi.org/10.1103/PhysRevB.61.10972