Bound and quasibound states in leaky quantum wells

In this work, we analyze a special type of quantum-well structure, called a ‘‘leaky’’ quantum well, which has an energy ‘‘window’’ opened near its bottom. It is shown that in this type of quantum well, whereas the upper states are bound states, the lower states located in the window are quasibound and hence allow the electron wave to leak out. The analysis, based on k⋅P theory, provides further support to the utilization of leaky quantum wells for intersubband lasing and reveals interesting well width and barrier thickness dependences of the lifetime of a lower quasibound state. Moreover, it is shown that an energy level in this type of quantum well could move either up or down as the barrier thickness increases, depending on whether it is above or below a stable point, the existence of which is also established in this work.