Some considerations on energy levels of quantum cascade lasers

Conduction band non-parabolicity is taken into account and a numerical method is proposed to calculate the electron subband energy levels and corresponding wave functions in the active region of quantum cascade lasers. For a coupled double-well vertical transition mode active region, the calculated Delta E-21 = 32 meV, Delta E-32 = 270 meV correspond, respectively, to the energy of an optical phonon and that of a photon at wavelength lambda = 4.5 mu m. For a coupled triple-well vertical transition active region, the calculated Delta E-21 = 32.4 meV, Delta E-32 = 250 meV correspond to the energy of an optical phonon and the photon energy at wavelength lambda = 5.0 mu m.