Short-wavelength quantum cascade lasers

Abstract

We report the first realization of short wavelength (λ ~ 3.05 - 3.6 μm) lattice matched In 0.53 Ga 0.47 As/AlAs 0.56 Sb 0.44 /InP quantum cascade lasers (QCLs). The highest-performance device (λ ~ 3.6μm) displays pulsed laser action for temperatures up to 300 K. The shortest wavelength QCL (λ ≈ 3.05 μm) operates in pulsed mode at temperatures only up to 110 K. The first feasibility study of the strain compensated InGaAs/AlAsSb/InP QCLs (λ ~ 4.1 μm) proves that the lasers with increased indium fractions in the InGaAs quantum wells of 60 and 70% display no degradation compared with the lattice matched devices having identical design. This strain compensated system, being of particular interest for QCLs at λ <~ 3.5μm, provides increased energy separation between the Γ and X conduction band minima in the quantum wells, thus decreasing possible carrier leakage from the upper laser levels by intervalley scattering. We also demonstrate that the performance of strain compensated InGaAs/AlAsSb QCLs can be improved if AlAsSb barriers in the QCL active region are replaced by AlAs layers. The introduction of AlAs is intended to help suppress compositional fluctuations due to inter diffusion at the quantum well/barrier interfaces.