Population inversion in step quantum wells at 10 /spl mu/m wavelength

In this work, it is shown that population inversion can be achieved between subbands in a step quantum well with a high width ratio based on carrier capture processes. It is known that in quantum well structures, emission of LO phonons is the main carrier capture mechanism. The LO-phonon scattering rate depends on the Froelich matrix element and the overlap of the initial and final wave functions squared. In a step quantum well with a high ratio of the step width to the well width the wave function overlap of the state in the step and the state in the well is reduced and thus a longer capture time results. If the carriers of the state in the well can be removed by an adjacent quantum well by tunneling, population inversion can be realized.