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Freeing Gallium Nitride Nanorods from Dislocations

posted Nov 12, 2012, 12:50 PM by R. Edwin García

Wide band gap III-nitride semiconductors used in light emitting diodes (LEDs), such as GaN, have the potential to deliver high quality illumination at an unprecedented performances. However, current epitaxial growth methods and device designs lead to technologies with relatively low efficiencies, particularly in the green wavelength portion of the spectrum. Here, a research team that includes graduate students Robert Colby, Zhiwen Liang, Isaac H. Wildeson, and David A. Ewoldt and as well as Professors Eric A. Stach, R. Edwin Garcia, and Timothy D. Sands has developed a GaN-based nanostructure design that favors dislocation filtering by selective area growth through a nanoporous template. These nanorods grow epitaxially from the (0001)-oriented GaN underlayer through the ~100 nm thick template and naturally terminate with hexagonal pyramid-shaped caps. The work demonstrates that for a certain window of geometric parameters a threading dislocation growing within a GaN nanorod is likely to be excluded by the strong image forces of the nearby free surfaces. The developed LED structures constitute a promising technology to enhance the efficacy and device lifetimes of residential and portable lighting diodes as compared to conventional planar heterostructures.

Researchers on this work include Professors R. Edwin Garcia, Timothy D. Sands and Eric A. Stach and graduate students

Robert Colby, Zhiwen Liang, Isaac H. Wildeson, David A. Ewoldt

(a) Schematic of  nanorods.  Bright field (b) and weak beam dark field (c) TEM images.

(a) Schematic of fabricated nanorods, illustrating filtering by the template within the nanorod. Bright field (b) and weak beam dark field (c) TEM images show a typical dislocation terminating near the base of a 50 nm diameter nanorod. With similar filtering observed for all dislocations intersecting 50 nm pores, these nanorods can be said to be essentially threading dislocation free.