Mid-IR quantum cascade lasers: Device technology and non-equilibrium Green's function modeling of electro-optical characteristics

In this paper, we report the results of investigation of 9.5 µm AlGaAs/GaAs and strain compensated 4.7 µm AlInAs/InGaAs/InP QCLs. We also show the results for 9.5 µm lasers based on lattice matched AlInAs/InGaAs/InP structures. The developed GaAs/AlGaAs lasers show the record pulse powers of 6 W at 77 K and up to 50 mW at 300 K. This has been achieved by careful optimization of the MBE growth process and by applying a high reflectivity metallic coating to the back facet of the laser. The 9.5 µm AlInAs/InGaAs/InP lasers utilize AlInAs waveguide and were grown exclusively by MBE without MOCVD regrowth. The short wavelength, strain compensated QCLs were grown by MOCVD. They represent state-of-the-art parameters for the devices of their design. For epitaxial process control, the atomic-force microscopy (AFM), high resolution X-ray diffraction (HR-XRD) and transmission electron microscopy (TEM) were used to characterize the morphological and structural properties of the layers. The basic electro-optical characterization of the lasers is provided. We also present results of Green's function modeling of mid-IR QCLs and demonstrate the capability of non-equilibrium Green's function (NEGF) approach for sophisticated but still computationally effective simulation of laser's characteristics.