Theoretical estimates of optimal parameters for quantum cascade lasers

Abstract

The quantum cascade (QC) laser is a new light source which is based on one type of carrier (electrons) making transitions between energy levels created by quantum confinement. In this paper, focusing on the working conditions which a QC laser should satisfy, we have discussed the subband lifespans in QC laser active regions. The results show that the population inversion condition can be achieved by resonant tunneling associated with an optical phonon, and this population inversion can be facilitated by the short escaping time of electrons from one active region to the neighboring active region. Our calculations also show that the lifespans of levels 3 and 2 are dominated by the phonon scattering time, and the escaping time from one active region to the next active region is determined by the thickness of exit barrier and the proper design of the miniband between the active regions.