Differential-gain damping in quantum dot lasers due to wetting layer states

Summary form only given. The laser must be considered as a coupled system in which the charge carrier distribution within the dots is mediated by the 2-D wetting layer. In this paper, we concentrate on the effect of the wetting layer on the differential gain. The wetting layer degeneracy is typically two orders of magnitude greater than the dots and so there is a large density of states at energies close to those of the dot states. This acts as a source of inertia, slowing the movement of the Fermi levels as charge is injected, and thus damping the differential gain. To investigate this effect experimentally, we have measured the modal gain as a function of injection current on a set of InGaAs quantum dot lasers emitting at a wavelength of 1 μm.