When conventionally calculating carrier leakage for state-of-the-art quantum cascade lasers (QCLs), that is, LO-phonon-assisted leakage from the upper laser level via electron thermal excitation to high-energy active-region (AR) states, followed by relaxation to low-energy AR states, ∼18%-wide gaps were recently found between calculated and experimentally measured internal efficiency values. We incorporate elastic scattering [i.e., interface-roughness (IFR) and alloy-disorder scattering] into the carrier-leakage process and consider carrier leakage from key injector states as well. In addition, the expressions for LO-phonon and IFR-triggered carrier-leakage currents take into account the large percentage of thermally excited electrons that return back to initial states via both inelastic and elastic scattering. As a result, we find that the gaps between theoretical and experimental internal efficiency values are essentially bridged. Another finding is that, for the investigated state-of-the-art structures, IFR scattering causes the total carrier leakage to reach values as much as an order of magnitude higher than conventional inelastic scattering-only leakage. The developed formalism opens the way to significantly increase the internal efficiency (i.e., to more than 80%) via IFR-scattering engineering, such that maximum wall-plug efficiencies close to projected fundamental, both-facets values (e.g., 42% at λ = 4.6 μm) can be achieved. By employing this formalism, we reached a 4.6 μm-emitting-QCL preliminary design for suppressing IFR-triggered carrier leakage, which provides an internal efficiency of 86% as well as a projected single-facet wall-plug efficiency value of 36% at a heatsink temperature of 300 K.

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Metalorganic chemical vapor deposition (MOCVD) growth of InP-based quantum cascade laser (QCL) structures on a Si (001) substrate is demonstrated by employing a metamorphic InP buffer layer with InAs/InP quantum dots as dislocation filters. Calibration samples consist of a strain-compensated 11.98 nm In 0.365 Al 0.635 As/14.8 nm In 0.64 Ga 0.36 As superlattice (SL) structure as well as 5-stages of the λ % 4.8 mm QCL active region, which are grown atop the metamorphic buffer and are used to assess the structural properties of the SL through high-resolution X-ray diffraction and high-resolution transmission electron microscopy. Full QCL structures with 40-stage active region are fabricated into edge-emitting ridge-waveguide structures and demonstrate low temperature electroluminescence with a FWHM of 48.6 meV.

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