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.

We report on detailed experimental investigation of thermal properties of AlGaAs/GaAs quantum cascade lasers (QCLs) emitting at wavelength of 9.4 μm. Different mounting options and device geometries are compared in terms of their influence on the relative increase of the active region temperature. High resolution, spatially resolved thermoreflectance is used for mapping temperature distribution over the facet of pulse operated QCLs. The devices’ thermal resistances are derived from experimental data. We also develop a numerical thermal model of QC lasers, solving heat transport equation in 2D and 3D, which includes anisotropy of thermal conductivity. By combining experimental and numerical results, an insight into thermal management in QCLs is gained. Thermal optimization of the design focuses on improving heat dissipation in the device, which is essential to increase the maximal operation temperature of the devices.

A methodological approach for advanced facet temperature characterization of operating diode lasers is presented. It relies on the concerted application of micro-Raman spectroscopy and thermoreflectance mapping. The latter technique allows for fast facet mapping, whereas the Raman data provide the temperature calibration. Residual effects, e.g., caused by the different reflectances of the materials involved into the laser structure, are discussed. Since both techniques provide rather complementary information, their concerted application appears as an effective tool for advanced device inspection.

This review focuses on theoretical foundations, experimental implementation and an overview of experimental results of the thermoreflectance spectroscopy as a powerful technique for temperature monitoring and analysis of thermal processes in semiconductor lasers. This is an optical, non-contact, high spatial resolution technique providing high temperature resolution and mapping capabilities. Thermoreflectance is a thermometric technique based on measuring of relative change of reflectivity of the surface of laser facet, which provides thermal images useful in hot spot detection and reliability studies. In this paper, principles and experimental implementation of the technique as a thermography tool is discussed. Some exemplary applications of TR to various types of lasers are presented, proving that thermoreflectance technique provides new insight into heat management problems in semiconductor lasers and in particular, that it allows studying thermal degradation processes occurring at laser facets. Additionally, thermal processes and basic mechanisms of degradation of the semiconductor laser are discussed.

A comprehensive investigation of the interfacial misfit (IMF) array formation has been carried out. The studies were based on the static phase diagram for GaAs (001) surface and As 2 dimers on the surface. Prior to the initiation of the GaSb growth two attempts of the temperature decreasing were performed: before and after the GaAs termination. The GaAs was grown in the optimal conditions for GaSb material. The influence of the interruption time on GaSb/GaAs heterostructure parameters was examined. Two cases were investigated: with and without Sb-soaking of the GaAs surface. The periodic array of edge dislocations at GaSb/GaAs interface was confirmed using Burger's circuit theory. Careful examination of misfit surroundings revealed one uncompleted Burger's vector that indicated one dislocation of mixed type among eight of the edge type. The distance between lattice sites of dislocations was 5.51 nm on average. The crystal quality of 5.0 µm GaSb layer was characterized by FWHM 2θ/ω = 42 arcsec, FWHM RC = 125 arcsec. The EPD = 4 × 10 6 cm − 2 was estimated after etching in FeCl 3 :HCl solution. The Δq z /Δq x ratio of 0.60 for 5.0 µm GaSb layer was higher than for 2.5 µm GaSb layer of 0.59. The probable reason was the thickness-dependent 60° dislocation density. The electrical parameters measured for 2.5 µm GaSb were: p = 4.0 × 10 16 cm −3 (2.0 × 10 16 cm −3 ) and µ = 599 cm 2 /V s (3420 cm 2 /V s) at 300 K (77 K).

The development of charge coupled device thermoreflectance (CCD TR) instrumentation for accurate and rapid evaluation of the thermal characteristics of quantum cascade lasers is demonstrated. The thermal characterization of such devices provides a mode for comparing different operating conditions, geometries and device designs. The method allows for registration of the high-resolution maps of the temperature distribution in a time not exceeding several seconds. The capabilities of the CCD TR are compared with standard TR spectroscopy.

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