COLLECTIVE EFFECTS IN THE INTERSUBBAND RESONANCE OF INAS ALSB QUANTUM-WELLS/

The consequences of a highly nonparabolic band structure on intersubba nd resonance are explored with experiments and theory on InAs/AlSb qua ntum wells. From a single-particle viewpoint, the intersubband resonan ce is expected to be broad because the intersubband spacing is highly k-dependent. Experimentally, however, we observe a relatively narrow l ine and this is interpreted as evidence that the intersubband resonanc e corresponds to a collective response of the high density electron sy stem. Calculations taking into account resonant screening reproduce th e 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 paral lel excitation where the matrix elements, although non-zero, are small . These results are confirmed experimentally by tilting the sample wit h respect to the light beam. (C) 1996 Academic Press Limited