Collective effects in the intersubband resonance of InAs/AlSb quantum wells

The consequences of a highly nonparabolic band structure on intersubband resonance are explored with experiments and theory on InAs/AlSb quantum wells. From a single-particle viewpoint, the intersubband resonance is expected to be broad because the intersubband spacing is highly k-dependent. Experimentally, however, we observe a relatively narrow line and this is interpreted as evidence that the intersubband resonance corresponds to a collective response of the high density electron system. Calculations taking into account resonant screening reproduce the experimental results reasonably well. Band nonparabolicity is shown from k . p theory to have no marked effects on the intersubband matrix elements both for conventional perpendicular excitation and for parallel excitation where the matrix elements, although non-zero, are small. These results are confirmed experimentally by tilting the sample with respect to the light beam. (C) 1996 Academic Press Limited