The impact of interface roughness (IFR)-scattering on the quantum efficiency of quantum-cascade lasers (QCLs) is demonstrated and analyzed both experimentally and theoretically. An InGaAs/InAlAs strain-compensated QCL emitting at λ ∼ 5.4 μm is analyzed in pulsed mode at liquid nitrogen temperatures. Measurements of the differential slope efficiency as a function of laser resonator length allow the pumping efficiency to be measured as a function of electron temperature. Excellent agreement is obtained when comparing the data to a calculation of the leakage current into higher-lying states via IFR-scattering, providing evidence of the importance of IFR-scattering on the QCLs quantum efficiency.

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25.

The values mc=0.043me, Λ = 6.0 nm, and Δ = 0.1 nm are used for calculations. The value for mc is calculated for the QCL structure presented in this work. The value for Λ is a typical one QCLs grown by molecular-beamy epitaxy (MBE).24 The value for Δ is then extracted from the measured value ΛΔ=0.6nm2.14 

26.

This can be estimated evaluating the limit τij0/τijIFR(ΔE)(1.64)γij, with γij=mcΛ2Eij/2. This results in τij0/τ(ΔE)2.72 for Eij= 100 meV. This value for Eij is a typical separation energy between the upper laser state and the excited miniband.

27.

The integral Iij(x0) varies weakly with electronic temperature. For example, between 200 and 400 K, the values of Iij(x0) range between 1.58 and 1.71 for Eij = 100 meV. Further, the variation of this integral with Eij is relatively weak. For a fixed temperature, a variation of Eij of 50% induces a variation of the integral Iij(x0) of ∼15%.

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