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Defense University Research Initiative on Nanotechnology
(DURINT) 2001
Nanoporous Templates for Large Defect
Reduction in SiC and GaN, Nanocatalysis,
Magnetic Clusters, and Biotechnology
Administered by the Office of Naval Research,
Program Manager: Colin Wood (woodce@onr.navy.mil)
Principal Investigator: Randall Feenstra (feenstra@cmu.edu)
Project Description
Nanoporous silicon carbide and gallium nitride templates will be exploited for wide bandgap semiconductor epitaxy and applications in magnetism, catalysis, and biotechnology. Dislocations in SiC and GaN films and substrates are electrically active, causing poor electronic and optoelectronic performance. We intend to reduce the density of defects by at least an order of magnitude in epitaxial SiC and some two orders of magnitude in epitaxial GaN by deposition on nanoporous SiC and GaN templates, and we will investigate the mechanisms of growth and defect (structural and point) reduction processes. Our porous templates will be the basis for nanocatalysis, biomedical applications in tissue engineering and microdialysis, and nano GaN:Mn clusters for high-density memory.
Our goal is to reduce the density of screw dislocations in epitaxial SiC layers to the 102-103 cm-2 range or below. We anticipate that reproducible GaN epitaxial device layers with mid 1015 cm-3 impurities and point defects, and structural defects in the range of 105 cm-2 or lower should be possible by our approach. Although the extended defect density has recently been significantly reduced with lateral epitaxial overgrowth (LEO), its complexity, together with the inhomogeneous nature of the resulting films, argues in favor of finding a simpler method for defect reduction. A type of nano-LEO process is expected to occur through suitable selective growth on porous SiC or porous GaN substrates. Because of the small length scale of the lateral growth region, coalescence of the films will be achieved without the misalignment found in conventional LEO.
Increased surface area provided by porous SiC and its inertness will be exploited in nano-surface catalysis. Nanoporous SiC/GaN systems are expected to be useful as active catalytic supports due to their high number of low-coordinated edge and corner sites, their high chemical and thermal stability, and the possibility for electrocatalysis reactions because of the semiconducting nature of the substrate. Research in this area will lead to improved methanol and related fuel cells as well as other heterogeneous catalytic systems.
SiC is biocompatible and porous SiC could make an excellent medium for semi-permeable membranes for microdialysis. Porous SiC membranes would be robust, thus enabling long term continuous monitoring of tissue, for early disease detection and other biosenor applications. It is also expected that porous SiC will make an ideal substrate on which a hydroxyapatite coating will adhere, which will then be employed for tissue growth. An effective means of interfacing biological systems with solid state devices will result, leading to better biological sensors e.g. which are needed to improve national readiness in the area of biochemical defense. Another application is devices such as strain gauges which could be mounted directly onto bone tissue thus providing a unique opportunity to monitor in situ the influence of strain-rate on the formation and growth of bone. This could have a potential impact on engineering the growth of new bone in tissue engineered bone grafts.
Exploiting SiC porous templates, we will deposit Mn doped GaN clusters for high-density robust storage applications. It has been predicted that wide bandgap semiconductors such as GaN potentially could have Curie temperatures above room temperature if they can be doped with magnetic ions such as Mn in sufficiently large quantity that will also produce holes (p-type conductivity). Employing porous SiC and porous GaN templates, together with AlN interlayers and selective growth schemes, we will investigate the formation of small GaN clusters and the incorporation of Mn or other magnetic ions in those clusters.