Optical gain and saturation in nitride-based laser structures

We have performed systematic studies of the optical gain and its saturation in (In, Ga)N/GaN/(Al, Ga)N laser structures that depend on the excitation density and number of quantum wells. The unsaturated gain factor which was obtained by the variable stripe-length method increases with excitation pow er, i.e., increasing modal gain. The gain factor also increases with a decr easing number of quantum wells, as is shown by the investigation of a serie s of laser structures with 3, 4, 5, and 10 quantum wells for fixed modal ga in. Values up to 40 dB at 300 K were measured. Thermal activation energies obtained by temperature dependent photoluminescence measurements yield info rmation on the influence of nonradiative recombination processes on optical gain saturation. (C) 2001 American Institute of Physics.