High performance materials and processing technology for uncooled 1.3 μm laser diodes

Abstract: This thesis investigates different material systems and processing technology for high temperature compatible laser diodes used in volume applications within the 1.3-μm telecom wavelength window. Laser diodes built from such materials are much desired in order to eleminate the need for active temperature control needed in current systems, which significantly increases both complexity, size and cost.The structures were grown by Metal-Organic Chemical Vapor Deposition (MOCVD) and the evaluation of materials was performed using different characterization methods such as High-Resolution X-Ray Diffraction (HR-XRD), Photoluminescence (PL), Time-Resolved Photoluminescence (TR-PL). Fabrication and evaluation of Fabry-Perot lasers with different geometries was used to check the material quality and temperature performance. A novel in-situ etching technique was developed for the use i future more advanced, buried hetrostructure lasers.The first studied materials system was AlGaInAsP/InGaAsP/InP. To handle a 5-element material with the precision required, modelling of the materials and heterostructure properties was performed. The addition of Al to the InGaAsP barrier allows better electron confinement with little change in valence band properties. The optimum aluminium content was found to be about 12%. Although the effect of Al could be identified, it was not sufficient with T0 of only 90 K only up to 60 °C. A second materials system InGaP/InAsP/ InP initially looked quite promising from a materials and quantum well design point of view but encountered severe problems with the device integration and further work was discontinued.The main effort was therefore was devoted to a third materials system: AlGaInAs/AlGaInAs/InP. This material system is not unknown but has hitherto not found a widespread application for fibre optic applications. In this work, the MOCVD growth of 1.3 μ;m quantum well laser structures was optimized and ridge waveguide laser devices with excellent temperature performance was fabricated (T0 = 97 K at 85 °C). A ridge waveguide laser was identified as suitable structure since it requires only a single epitaxial growth, thus avoiding the main problem of oxidation of Al based buried structures. The dynamic performance was excellent up to 110 °C and the device fabrication is highly reliable (lifetime >7000 h). This high yield uncooled ridge Fabry-Perot laser process has now been transferred to production and is applied in short length 10 Gb/s multimode links.In order to further improve the usefulness of the Al-containing materials in even higher performance devices needed in future applications developments towards fully buried heterostructure device geometry were also pursued. To overcome difficulty of oxidation of Al containing layers at the mesa walls an in-situ etching technique was implemented. Different chemistry approaches were investigated and the first results of lasers devices were reported.