Space charge and many-body effects on the optical gain in semiconductor quantum wells for advanced laser design

Abstract

A sophisticated design on quantum well active layers is required to meet the recent demands for functional optoelectronic devices and high performance laser diodes. Conventional studies on optical gain in quantum wells have been devoted to ideal quasi-two-dimensional systems, so that only a little attention has been paid for the spatial distribution of carriers. In GaInP/AlGaInP or InGaAs/InGaAsP quantum wells, which are widely used in current applications, electrons are less confined to the wells than holes and result in a strong spatial charge effect. We have developed a density functional theory to study the effects of the valence band mixing, space charge potential, and the exchange-correlation potential on the sub-band structures and the optical gain in quantum wells. The energy levels and wave functions for electrons and holes were calculated self-consistently. Non-Markovian intraband relaxation is also included in the gain calculation. Numerical calculation shows the necessity of both the space charge potential and the exchange-correlation potential to obtain accurate sub-band energies and optical gain. We will show the advantages of the present method and discuss further improvement.