Intersubband transitions in an asymmetric quantum well with a thin barrier or a delta-function potential

The changes in the bound-state energies and oscillator strength for intersubband transitions brought about by a thin barrier in the middle of an asymmetric quantum well are calculated, with a particularly close look at such changes as the middle barrier height approaches the bound-state energies. It is found that the oscillator strength goes through a slight change as the barrier height approaches the ground-state energy but an abrupt change when it approaches the excited bound-state energy. A suitable explanation for this change is provided. A similar tailoring of the intersubband transitions is also achieved by placing a delta-function potential in the vicinity of the middle of the well but without any abrupt change in the oscillator strength.