High-power inter-miniband lasing in intrinsic superlattices

We report the realization of a mid-infrared (λ≃7μm) quantum-cascade laser, in which the emission process takes place between the two lowest minibands of an intrinsic superlattice. Contrary to previous lasers based on doped superlattices, here the dopants are located only inside suitably designed injector regions, where positive ionized donors and negative electrons are arranged to compensate the applied external field across the superlattices. This reduces impurity scattering and translates into low threshold currents (4.2kA/cm² at 10 K) and into room temperature operation, without compromising the large current-carrying capabilities of the minibands. Peak powers of ∼1.3W per facet have been obtained from broad-area devices at 10 K, with still more than 1 W at 120 K and 400 mW at 200 K. Effects related to the finite size of the superlattices become visible in the spectral properties, owing to the reduced broadening, and have to be taken into account to accurately describe the laser's behavior.