Intersubband transitions in quantum well heterostructures with delta-doped barriers

A single quantum well doped by a negative delta-function potential (δ-potential) in the barrier regions is analyzed in terms of the optical transitions in between subbands. The first two states of the quantum well do not change at all as a function of the strength of the δ-potential up to a certain value, whereas the third one gets lowered almost exponentially. An important point is that the δ-potential brings a state from the continuum to the bound region. There is a range of the strength of the δ-potential during which the transition energy for the first to second state decreases rapidly, and at a certain strength the first and second states disappear, and the third and fourth, which have been brought from the continuum, take their places. The oscillator strengths of the allowed transitions have a kind of oscillatory behavior in that range.