Study of ELOG GaN for Application in the Fabrication of Micro-channels for Optoelectronic Devices
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Study of ELOG GaN for Application in the Fabrication of Micro-channels for Optoelectronic Devices L. E. Rodak, N. J. Berry Ann, Kalyan Reddy Kasarla, Nanying Yang, D. Korakakis Lane Department of Computer Science and Electrical Engineering West Virginia University PO Box 6109, Morgantown, WV 26506-6109 ABSTRACT Gallium Nitride (GaN) is a promising wide band gap semiconductor material for many optoelectronic applications, especially in the near UV range. Over the past several years, an extensive technical effort has been focused on improving the quality of GaN films through various overgrowth techniques such as epitaxial lateral overgrowth (ELOG), facet controlled epitaxial lateral overgrowth (FACELO), and Pendeoepitaxy. ELOG has been shown to reduce the density of threading dislocations by up to five orders of magnitude [1], however a complete physical model describing lateral overgrowth is needed in order to take full advantage of the process. A lateral overgrowth model will allow for the design and fabrication of three dimensional structures that can lead to novel devices and also to efficient biosensors by integrating micro and nano channels on the same chip as the optoelectronic components. A two-step process has been used to successfully control the geometry of overgrown GaN. Conditions have been identified which give a reduced lateral growth rate, in order to allow expansion of the {112n} plane to form vertical sidewalls and for the design of channel width. These geometries are being examined for possible application in laser diode and micro-channel fabrication for integrating bio-agent detection modules. INTRODUCTION
Gallium Nitride (GaN) is a promising semiconductor for use in many electronic and optoelectronic applications due to its temperature stability and wide band gap. Electronic implementations include, but are not limited to, high power and high temperature applications such as in automobiles, aircrafts, and space shuttles. Furthermore, the bandgap of GaN makes it ideal for emission in blue region while the band gap of the binary and ternary alloys in (Al, In, Ga)N can be adjusted for emission over the entire visible spectrum and into the ultra violet (UV) region. This is useful for the fabrication of light emitting diodes (LEDs), laser diodes (LDs), and UV detectors. Applications include solid state lighting, solar blind detectors, and bio-agent detection [1]. Because GaN is not available in bulk, it is typically grown by heteroepitaxy using Metal Organic Chemical Vapor Deposition (MOCVD), Molecular Beam Epitaxy (MBE), or Hydride Vapor Phase Epitaxy (HVPE). Typical substrates include sapphire, silicon carbide, and silicon. The lattice mismatch between the substrate and GaN causes a high density of threading dislocations to propagate through the material and reduce the lifetime and efficiency of devices fabricated from this material.
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b Figure 1 – (a) Prepared ELOG Sample (b) Initial ELOG Growth (c) Fully Coalesced ELOG Growth
One common method used to reduce
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