Nonlinear effects of the optical gain in the quantum well laser diodes

Abstract

The basic equations for modeling the dynamic characteristics of semiconductor lasers are the rate equations. One of their main parameters is the gain, which is defined by the optical gain coefficient. The linear form of this coefficient describes correctly the real behaviour of the laser under small pumping currents, however as the present research has shown, for a large electron density the gain is saturated and the dependence becomes nonlinear and that should be taken into account in the dynamic model. To determine the acceptable form of the gain in the set of the rate equations, we carry out an analysis of the carrier density influence on the optical gain taking into account the carriers density influence on the quasi-Fermi-level for the conduction and valence bands. We consider the differences in characteristics of lasers with bulk and quantum well (QW) active layers. The original function of the total density of the state dependence on the energy for QW lasers is proposed and used to reduce the computation time.