Analyses of Optical Gains and Oscillation Wavelengths for Quantum Cascade Lasers Using the Nonequilibrium Green’s Function Method

Abstract

We have succeeded in improving the gain of the base quantum cascade laser (QCL) through experiments and device simulations using the nonequilibrium Green’s function (NEGF) method, and we investigate the factor that increases the gain by reducing the thickness of the barrier by 10%. Specifically, we analyzed the minibands (Wannier–Stark states), density of states (DOS), and electron density that contribute to the emission. The results show that the gain enhancement is due to the increase in the electron density of the quantum wells in the active region and the increase in the oscillator strength between the minibands that contribute to the emission. Quantum mechanical calculation like the NEGF method is very effective for mesoscopic systems such as the active layer of QCL.

GA