Investigation of non-equilibrium steady-state gain in semiconductor quantum wells

A dynamic quantum well (QW) gain model is presented, which is used to investigate non-equilibrium steady-state gain in a QW, under CW electrical and optical excitations. Intrasubband, intersubband and interband carrier-carrier and carrier-phonon scattering processes are distinguished. Carrier capture/escape is modelled as a carrier-carrier scattering process and includes the solution of Poisson's equation, such that deviations from QW charge neutrality lead to a modification of the capture rate through band bending. Radiative transitions are modelled using a Fermi's Golden Rule approach. Carrier-carrier scattering is described using the standard relaxation rate approximation. A different approach is adopted for carrier-phonon interactions to account for the carrier kinetic energy thresholds, which exist for intrasubband and intersubband carrier-phonon scattering by phonon emission and absorption. Results show that significant non-equilibrium conditions exist, even in the absence of stimulated emission, and have implications for the use of thermal equilibrium carrier distributions in full laser diode simulation tools.