Theoretical model for intravalley and intervalley free-carrier absorption in semiconductor lasers: beyond the classical Drude model

Free-carrier absorption is calculated from the second-order perturbation theory of quantum mechanics by considering the interactions between carriers and polar optical phonons, deformation potential optical phonons, deformation potential acoustic phonons, piezoelectric acoustic phonons, and charged impurities in the intravalley transition and the intervalley transition. A formula is derived from our theoretical model for the coefficient of free-carrier absorption by incorporating the state-filling effect and the degenerate carrier distribution. Our results indicate that the classical Drude model is inadequate to describe many features of the free-carrier absorption. Alternatively, our theoretical model may provide an efficient method for investigating the effect of free-carrier absorption on the functionality or performance of the related optoelectronic device.