Design and Realization of Novel GaAs Based Laser Concepts

Abstract

ZusammenfassungHalbleiterlaser stellen die Grundlage für eine zunehmende Vielzahl von Anwendungen dar, die von der Informationsspeicherung und digitalen Kommunikation bis hin zur Materialbearbeitung reichen. Neuartige Konzepte überwinden bisherige Limitierungen und erschließen neue Anwendungsgebiete. Viele dieser Anwendungsgebiete verlangen nach kostengünstigen Bauelementen, die maximale Brillanz und hohe Ausgangsleistungen oder höchste Geschwindigkeiten erreichen.Diese Arbeit stellt dar, wie essentielle Leistungsmerkmale von Halbleiterlasern durch das Design von Nanostrukturen und epitaktischen Wachstumsprozessen maßgeschneidert werden können. Hierbei wird auf alle Schritte der Laserherstellung eingegangen, vom Design über das Wachstum der Nanostrukturen mittels metallorganischer Gasphasenepitaxie (MOVPE), bis hin zur Herstellung und Charakterisierung kompletter Bauelemente. AbstractSemiconductor lasers represent the backbone for an increasing variety of applications ranging from information storage and communication, to material treatment. Novel concepts are pushing the limits and are enabling new application areas. Many of these areas demand low-cost laser devices with high-brilliance and high-power light output or high-speed performance.This thesis demonstrates how key performance characteristics of semiconductor lasers can be tailored using nanostructure design and epitaxial growth. All aspects of laser fabrication are discussed, from design to growth of nanostructures using metal-organic vapor-phase epitaxy (MOVPE), to fabrication and characterization of complete devices. By employing industrial tools, all developed processes are compatible with mass production.Pulsed high power laser operation up to 8 W and a ultra-low lasing threshold of 66 A/cm 2 is achieved with electrically pumped quantum dots (QD)-based edge emitters at 1.25 µm due to an improved understanding of the QD growth process. This novel process enables 1.3 µm edge emitters for telecom applications in the established InGaAs/GaAs system. At the heart of these achievements is the careful investigation and optimization of nearly all layers of the laser device structure. Designs are altered and precisely tuned by employing AlGaAs or InGaP claddings and varied doping schemes in order to develop new waveguides to meet different requirements.High-power vertical external-cavity surface-emitting lasers (VECSELs) promise continuous-wave (CW) lasing with perfect circular beam quality, plus direct access to the cavity. While the concept is ideal for a multitude of applications, conventional quantumwell based systems exhibit problematic temperature sensitivity during operation. Here, for the first time, VECSELs with sub-monolayer structures and QDs as active layers are realized by MOVPE. These optically pumped devices cover a wide spectral range from 950 nm to 1210 nm, and achieve excellent temperature-stable CW lasing due to the use of QDs and CW output powers of up to 1.4 W.In order to overcome the physical limitations of directly modulated vertical-c...