Advanced GaAs Based Laser Fabrication (Feasibility Study)

GaAs materials research has extended the operating wavelengths of devices to those used in telecommunications and medical diagnostic applications, and offers a number of advantages over incumbent InP based devices. These revolve around the use of larger substrates leading to cost reductions, and greater band offsets allowing higher temperature (or uncooled) operation of a device through improved carrier confinement. However, GaAs based device fabrication is rather immature, with GaAs lasers typically only available as Fabry-Perot ridge structures, which exhibit highly asymmetric output, surface recombination, and broad emission spectra. Technologies such as distributed feedback (for single mode operation) and buried heterostructure lasers (symmetric output, reduced surface losses) are commonplace in commercial InP devices. The development of GaAs based buried heterostructure devices in this proposal relies upon a novel approach in circumventing deleterious regrowth upon exposed AlGaAs, allowing buried heterostructure technology for GaAs based materials. GaAs based buried heterostructure lasers will be developed and assessed in terms of electrical and optical performance, in particular the spatial profile of the optical emission using far field analysis techniques. Solid source and gaseous epitaxial overgrowth methods will be assesed and compared under various conditions. Buried gratings (distributed feedback) will be developed, initially for use in a single mode ridge laser, before ultimately incorporation in a buried heterostructure distributed feedback laser.