Abstract
We present theoretical results bearing on the energy position and spatial localization of the low-lying "barrierlike" states (i.e., states which are not bound in the narrow well) in semiconductor separate confinement heterostructures. We show that under most circumstances these states are less localized than classically expected. However, when a virtual bound state of the narrow well occurs near the onset of the narrow-well continuum or when a state has just been bound by this well, the quantum-well-projected density of states of the system is much larger than in nonresonant situations. This points out the possible influence of the virtual bound states in the mechanism of carrier capture by the quantum well.