New optical structure near theEtransitions of InSb/InAlSb quantum wells

We use resonant Raman scattering to probe into the electronic structure of InSb/InAlSb strained layer superlattices in the region of the $B_1$ optical gap. A new resonant enhancement peak, not present in bulk InSb, appears in narrow quantum-well samples at low temperatures. Its dependence of quantum-well width and temperature indicates the existence of another critical point in the combined density of states that becomes observable through excitonic interactions under extreme confinement of the electronic states. A similar structure is observed in GaSb/GaAlSb quantum wells. This suggests the presence of two critical points along the Λ direction of the Brillouin zone in the bulk semiconductors of this family.