Quantum Cascade Lasers On Algaas Gaas For The Mid Infrared Regime

This book describes the physics, fabrication technology, and applications of the quantum cascade laser.

This thesis presents the first comprehensive analysis of quantum cascade laser nonlinear dynamics and includes the first observation of a temporal chaotic behavior in quantum cascade lasers. It also provides the first analysis of optical instabilities in the mid-infrared range. Mid-infrared quantum cascade lasers are unipolar semiconductor lasers, which have become widely used in applications such as gas spectroscopy, free-space communications or optical countermeasures. Applying external perturbations such as optical feedback or optical injection leads to a strong modification of the quantum cascade laser properties. Optical feedback impacts the static properties of mid-infrared Fabry–Perot and distributed feedback quantum cascade lasers, inducing power increase; threshold reduction; modification of the optical spectrum, which can become either single- or multimode; and enhanced beam quality in broad-area transverse multimode lasers. It also leads to a different dynamical behavior, and a quantum cascade laser subject to optical feedback can oscillate periodically or even become chaotic. A quantum cascade laser under external control could therefore be a source with enhanced properties for the usual mid-infrared applications, but could also address new applications such as tunable photonic oscillators, extreme events generators, chaotic Light Detection and Ranging (LIDAR), chaos-based secured communications or unpredictable countermeasures.

A state-of-the-art overview of this rapidly expanding field, featuring fundamental theory, practical applications, and real-life examples.

When using conventional substrates, such as InP and GaAs, the materials constituting the superlattice (SL) core region of the quantum cascade laser (QCL) are constrained by strain-induced critical-thickness limitations. Metamorphic buffer layers (MBLs) can serve as "virtual substrates" with a designer-chosen surface lattice constant, thus expanding the compositional-design space for a variety of device structures, including short-wavelength QCLs. An optimized short-wavelength (3.4 [mu]m) single-phonon-resonant (SPR)+ miniband extraction QCL design, grown on an [InxGa1-xAs] MBL, is presented along with the optical and thermal device considerations in play. MBLs can be grown with a variety of graded regions such as linear composition grade from GaAs to [InxGa1-xAs] or by employing dislocation filters between Si substrate and InP. QCL and test superlattices' regrowth on these MBLs with the corresponding materials and device analysis, is presented in this work. In addition to the materials limitation for the design of QCL devices, the requirement to have the constituent layers (1-5 nm) to be precisely controlled in the various compositions and thicknesses, is a challenge. Interfacial grading in strained SLs is studied via atom probe tomography for SLs with various layer thicknesses and relative lattice strains. The tip reconstructions are analyzed by fitting the interfaces to diffusion profiles. Mechanisms possible for the observed interdiffusion profile, such as surface segregation and/or bulk diffusion, are discussed. With an understanding of the compositional gradient at the interfaces, together with optimized QCL designs and regrowth on the MBLs, short-wavelength QCLs with high performances can be achieved

The objectives of this program were threefold: to reproduce the quantum cascade laser results from Bell Labs in a production environment, to demonstrate the quantum cascade laser at longer wavelengths, and to extend the technology to the GaAs/AlGaAs material system in order to make the lasers easier to produce. After characterization with 5-crystal x-ray diffraction and photoluminescence to verify the material quality three laser wafers, with anticipated operating wavelengths near 4.5 microns and 8.5 microns, were grown, processed, and tested for this program. Although we were able to successfully grow the very thick lattice matched layers necessary for these devices, no lasing or electroluminescence was observed from any of the samples. Another laser design was produced based on the reported quantum cascade laser structures, but utilizing GaAs and AlGaAs materials instead of InGaAs and InAlAs; however, because of the negative results with the InGaAs/InAlAs structure and additional design uncertainties for the AlGaAs materials, this structure was not grown. This report will discuss in detail the work that was performed on the contract, possible cause for the negative results, and conclusions drawn from the work.