Built-in electric field minimization in (In, Ga)N nanoheterostructures.

(In, Ga)N nanostructures show great promise as the basis for next generation LED lighting technology, for they offer the possibility of directly converting electrical energy into light of any visible wavelength without the use of down-converting phosphors. In this paper, three-dimensional computation of the spatial distribution of the mechanical and electrical equilibrium in nanoheterostructures of arbitrary topologies is used to elucidate the complex interactions between geometry, epitaxial strain, remnant polarization, and piezoelectric and dielectric contributions to the self-induced internal electric fields. For a specific geometry-nanorods with pyramidal caps-we demonstrate that by tuning the quantum well to cladding layer thickness ratio, h(w)/h(c), a minimal built-in electric field can be experimentally realized and canceled, in the limit of h(w)/h(c) = 1.28, for large h(c) values.

Controlled growth of ordered nanopore arrays in GaN.

High-quality, ordered nanopores in semiconductors are attractive for numerous biological, electrical, and optical applications. Here, GaN nanorods with continuous pores running axially through their centers were grown by organometallic vapor phase epitaxy. The porous nanorods nucleate on an underlying (0001)-oriented GaN film through openings in a SiN(x) template that are milled by a focused ion beam, allowing direct placement of porous nanorods. Nanopores with diameters ranging from 20-155 nm were synthesized with crystalline sidewalls.

Dislocation filtering in GaN nanostructures.

Dislocation filtering in GaN by selective area growth through a nanoporous template is examined both by transmission electron microscopy and numerical modeling. These nanorods grow epitaxially from the (0001)-oriented GaN underlayer through the approximately 100 nm thick template and naturally terminate with hexagonal pyramid-shaped caps. It is demonstrated 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. Approximately 3000 nanorods were examined in cross-section, including growth through 50 and 80 nm diameter pores. The very few threading dislocations not filtered by the template turn toward a free surface within the nanorod, exiting less than 50 nm past the base of the template. The potential active region for light-emitting diode devices based on these nanorods would have been entirely free of threading dislocations for all samples examined. A greater than 2 orders of magnitude reduction in threading dislocation density can be surmised from a data set of this size. A finite element-based implementation of the eigenstrain model was employed to corroborate the experimentally observed data and examine a larger range of potential nanorod geometries, providing a simple map of the different regimes of dislocation filtering for this class of GaN nanorods. These results indicate that nanostructured semiconductor materials are effective at eliminating deleterious extended defects, as necessary to enhance the optoelectronic performance and device lifetimes compared to conventional planar heterostructures.