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

Abstract

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.