Templated and 3D growth
In addition to nanowires, we are also interested in using nano and microstructures as templates for improving material quality and creating novel structures & new functionalities. We have developed a patented technique that uses vertically aligned GaN nanowire arrays as a high quality template for the growth of high quality GaN films on inexpensive, lattice-mismatched substrates, as shown in the accompanying figure. The nanowires serve as strain compliant "bridges" between the coalesced GaN film and the underlying, lattice-mismatched sapphire substrate, which helps to minimize formation of extended defects in the GaN film which are detrimental to LED and laser diode lifetimes and efficiencies.
We have also developed another technology that uses self-assembled monolayers of silica nano-to-microspheres as defect-filtering growth templates. By selectively growing GaN through the voids of the sphere layers, threading dislocation densities can be reduced to the mid 107 cm-2 range without the use of costly lithographic templates or thick bulk-like layers. The spheres also provide a route for chemical lift-off of the III-nitride layers, rather than more expensive laser lift-off methods currently used.
Q. Li, J. J. Figiel, and G. T. Wang, “Dislocation density reduction in GaN by dislocation filtering through a self-assembled monolayer of silica microspheres,” Applied Physics Letters 94(23), (2009). [link]
Q. Li, Y. Lin, J. R. Creighton et al., “Nanowire-templated lateral epitaxial growth of low-dislocation density nonpolar a-plane GaN on r-plane sapphire,” Advanced Materials 21(23), 2416-2420 (2009). [link]
Nanowire templated GaN growth
Sphere templated GaN growth