| About this Abstract |
| Meeting |
2010 Electronic Materials Conference
|
| Symposium
|
TMS 2010 Electronic Materials Conference
|
| Presentation Title |
Y2, Threading Defect Elimination in GaN Nanostructures |
| Author(s) |
Ashwin Krishnan Rishinaramangalam, Stephen D Hersee, Michael Fairchild, Lei Zhang, Petros Varangis |
| On-Site Speaker (Planned) |
Ashwin Krishnan Rishinaramangalam |
| Abstract Scope |
This paper describes the elimination of threading dislocations (TDs) in GaN nanowire and nanowall structures grown by Metal Organic Chemical Vapor deposition (MOCVD). The templated nanostructure growth process uses high-purity metal organic and ammonia precursors as in regular MOCVD growth, and avoids the use of metal catalysts. The nanostructures were grown selectively onto underlying planar (0001) GaN films using nano-patterned templates. The threading defect density in the underlying planar GaN film was in the range 10<SUP>8</SUP> to 10<SUP>9</SUP> cm<SUP>-2</SUP>. TDs were imaged using bright-field cross-sectional transmission electron microscopy (XTEM) analysis of thinned nanowire and nanowall samples.
The density of threading defects in [0001] GaN nanowires approaches zero even though these nanostructures are epitaxially connected to an underlying planar GaN film that has a defect density in the range 10<SUP>8</SUP> to 10<SUP>9</SUP> cm<SUP>-2</SUP>. XTEM reveals that the nominal [0001] line direction of a TD changes when that TD enters a GaN nanostructure. The line direction of the TDs bends towards the (0001) plane, and the dislocation rapidly terminates at a {1-100} sidewall facet of the nanostructure. We propose that the driving force for this elimination process is the reduction of the dislocation line energy. This line energy is reduced for a TD that bends and terminates at a sidewall compared to a TD that continues to propagate along the nanowire. A simple model is also proposed, where in the TDs are shown to bend and terminate at a sidewall simply by climb. A conversion to another defect-type does not appear to be required and furthermore, conversion to a different defect is expected to be energetically unfavorable. This TD elimination mechanism is expected to be active in any [0001] GaN nanostructure, where a surface is in close proximity to the threading defect.
Nanostructures clearly offer a unique opportunity to fabricated defect-free GaN-based devices.
Acknowledgment: This work was supported in part by the Engineering Research Centers Program of the National Science Foundation under NSF Cooperative Agreement No. EEC-0812056. Any Opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect those of the National Science Foundation. |
| Proceedings Inclusion? |
Undecided |