A major challenge in understanding commercial MOCVD reactors is to simultaneously model both the complex chemistry and the complex fluid flow. Sandia scientists have developed research MOCVD reactors to expedite model development. The use of simple geometries facilitates the task of separating the effects of heat and mass transfer from the effects of chemical reactions. Our rotating disk reactors are specifically designed to provide good optical access.
Flow visualization of gas-flow patterns in CVD systems is useful for studying recirculation patterns, gas injection and gas mixing, and for confirmation of fluid-mechanical models. CVD scientists have used laser-light scattering from particles seeded in the gas flow to study flow patterns in a rotating disk reactor, UV absorption of non-fluorescing reactants in a channel-flow reactor, and imaging of laser-induced fluorescence to examining gas-mixing for a concentric injector. Scattering of laser light is also useful as a detector of particulates in process gas.
Optical diagnostics are ideally suited to probing the hostile environment of a MOCVD system. They are non-intrusive, selective, sensitive, and can provide the high spatial resolution needed in the strong temperature and concentration gradients present in MOCVD processes. Sandia researchers have extensive experience in developing and applying such techniques to reacting flows, including MOCVD and combustion systems.
Advanced Materials Sciences has a complete set of modern surface-sensitive analytical techniques for elucidating mechanisms and kinetics of surface chemistry. The available techniques include LEED, Auger, XPS, static-SIMS, TPD, FTIR and molecular beam scattering. These techniques are available in multi-chambered systems that integrate high-pressure processing chambers with UHV environments. This approach enables the isolation and study of key reactions in MOCVD systems as well as the in-situ characterization of nanostructures grown by MOCVD or Molecular Beam Epitaxy (MBE). Ongoing programs are investigating the chemistry of GaInAlN materials, devices, and nanostructures.
Sandia maintains state-of-the-art materials growth and characterization facilities, particularly in Metal-Organic Chemical Vapor Deposition (MOCVD). MOCVD is used for commercial production of compound semiconductor materials because of its ability to grow compositionally tailored and artificially structured materials (e.g., monolayer superlattices), its capacity for high through-put, and its relatively low cost. Sandia's facilities include six commercial MOCVD reactors that are used to grow device-quality epitaxial films and superlattices of aluminum, gallium and indium nitride, arsenide, phosphide, and antimonide materials. The newest of these reactors, a Veeco P125 Rotating Disk Reactor, is specifically targeted for the development of a variety of AlGaN devices for National Security needs as well as Solid State Lighting. A variety of techniques are used for materials characterization, including optical microscopy, electron microscopy (scanning or transmission), x-ray diffraction, Hall measurements, and photoluminescence.