Dislocation Filtering in GaN Nanostructures

School of Materials Engineering, Purdue University, West Lafayette, IN 47907, USA.
Nano Letters (Impact Factor: 13.59). 05/2010; 10(5):1568-73. DOI: 10.1021/nl9037455
Source: PubMed


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.

24 Reads
  • Source
    • "The small lateral dimensions of the NRs enable the growth of high quality GaN on lattice mismatched substrates like sapphire or silicon [1] [2]. The bending of defects towards the NR surface was identified to be one major pathway of defect reduction during the growth of nanostructures [3] [4] [5]. NRs are used for fabrication of defect reduced templates. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Nano Imprint Lithography (NIL) is a promising technology that combines low costs with high throughput for fabrication of sub 100 nm scale features. One of the first application areas in which NIL is used is manufacturing of various types of LED's. The wafers used for producing LED's are typically III/V semiconductor materials grown with epitaxial processes. These types of substrates suffer from growth defects like hexagonal spikes, vpits, waferbowing, atomic steps and surface corrugations on a scale of few 10 mum or even large islands of irregularities. The mentioned irregularities are particularly disturbing when NIL based processes are utilized to create patterns onto the wafer surface. The nanopatterns created by NIL can be applied to control metal organic vapour phase epitaxy (MOVPE) growth of GaN nanorods. This paper will show that NIL is an excellent technology to produce nanopatterned GaN substrates highly suitable to grow defect free arrays of positioncontrolled nanorods for ultrahigh brightness LED applications.
    Proceedings of SPIE - The International Society for Optical Engineering 03/2011; 7970. DOI:10.1117/12.879368 · 0.20 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Nanopyramid light emitting diodes (LEDs) have been synthesized by selective area organometallic vapor phase epitaxy. Self-organized porous anodic alumina is used to pattern the dielectric growth e templates via reactive ion etching, eliminating the need for lithographic processes. (In,Ga)N quantum well growth occurs primarily on the six {1 (1) over bar 01} semipolar facets of each of the nanopyramids, while coherent (In,Ga)N quantum dots with heights of up to similar to 20 nm are incorporated at the apex by controlling growth conditions. Transmission electron microscopy (TEM) indicates that the (In,Ga)N active regions of the nanopyramid heterostructures are completely dislocation-free. Temperature-dependent continuous-wave photoluminescence of nanopyramid heterostructures yields a peak emission wavelength of 617 nm and 605 nm at 300 K and 4 K respectively. The peak emission energy varies with increasing temperature with a double S-shaped profile, which is attributed to either the presence of two types of InN-rich features within the nanopyramids or a contribution from the commonly observed yellow defect luminescence close to 300 K. TEM cross-sections reveal continuous planar defects in the (In,Ga)N quantum wells and GaN cladding layers grown at 650-780 degrees C, present in 38% of the nanopyramid heterostructures. Plan-view TEM of the planar defects confirms that these defects do not terminate within the nanopyramids. During the growth of p-GaN, the structure of the nanopyramid LEDs changed from pyramidal to a partially coalesced film as the thickness requirements for an undepleted p-GaN layer result in nanopyramid impingement. Continuous-wave electroluminescence of nanopyramid LEDs reveals a 45 nm redshift in comparison to a thin-film LED, suggesting higher InN incorporation in the nanopyramid LEDs. These results strongly encourage future investigations of III-nitride nanoheteroepitaxy as an approach for creating efficient long wavelength LEDs.
    Journal of Applied Physics 08/2010; 108(4). DOI:10.1063/1.3466998 · 2.18 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The effect of image forces in GaN pyramidal nanorod structures is investigated to develop dislocation-free light emitting diodes (LEDs). A model based on the eigenstrain method and nonlocal stress is developed to demonstrate that the pyramidal nanorod efficiently ejects dislocations out of the structure. Two possible regimes of filtering behavior are found: (1) cap-dominated and (2) base-dominated. The cap-dominated regime is shown to be the more effective filtering mechanism. Optimal ranges of fabrication parameters that favor a dislocation-free LED are predicted and corroborated by resorting to available experimental evidence. The filtering probability is summarized as a function of practical processing parameters: the nanorod radius and height. The results suggest an optimal nanorod geometry with a radius of ∼50b (26 nm) and a height of ∼125b (65 nm), in which b is the magnitude of the Burgers vector for the GaN system studied. A filtering probability of greater than 95% is predicted for the optimal geometry.
    Journal of Applied Physics 11/2010; 108(7-108):074313 - 074313-8. DOI:10.1063/1.3491024 · 2.18 Impact Factor
Show more

Similar Publications