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Effect of interfacial strain on shape and composition of MOCVD grown III-Nitride nanostructures

Published online by Cambridge University Press:  01 February 2011

Vibhu Jindal
Affiliation:
[email protected], College of Nanoscale Science and ENgineering, Nanotechnology, 255 Fuller Road, University at Albany, Albany, NY, 12203, United States
James Grandusky
Affiliation:
[email protected], College of Nanoscale Science and Engineering, 255 Fuller Road, University at Albany, Albany, NY, 12203, United States
Neeraj Tripathi
Affiliation:
[email protected], College of Nanoscale Science and Engineering, 255 Fuller Road, University at Albany, Albany, NY, 12203, United States
Mihir Tungare
Affiliation:
[email protected], College of Nanoscale Science and Engineering, 255 Fuller Road, University at Albany, Albany, NY, 12203, United States
Fatemeh Shahedipour-Sandvik
Affiliation:
[email protected], College of Nanoscale Science and Engineering, 255 Fuller Road, University at Albany,, Albany, NY, 12203, United States
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Abstract

It is determined that the interfacial strain due to lattice mismatch between the substrate (template) and the overgrown nanostructure has substantial influence on the final morphology and faceting of nanostructures. AlGaN and GaN nanostructures were grown on different substrates/templates, namely Sapphire, AlN/Sapphire, Al0.5Ga0.5N/Sapphire and GaN/Sapphire, where interfacial strain for overgrown nanostructures changes from compressive to tensile respectively. GaN nanostructures grown by metalorganic chemical vapor deposition (MOCVD) using identical growth parameters exhibit pyramidal morphologies under low or no mismatch strain, while highly strained structures with compressive strain evolve into prismatic shapes when grown in the c-crystallographic direction. In addition, it is shown that interfacial strain also affects the growth rate and alloy composition of ternary AlGaN nanostructures produced under identical conditions on different templates/substrates. AlGaN nanostructures grown under compressive strain show higher vertical and lower lateral growth rates when compared to those under tensile strain. Scanning electron microscopy, transmission electron microscopy and cathodoluminescene were used to characterize growth rates, shape and composition of the nanostructures. Observed variation in morphologies, growth rates and compositions are explained in terms of the strain dependency of adatom diffusion barriers on strained surfaces and Ehrlich-Schwoebel barriers across different crystallographic planes. Density functional (DFT) calculations were performed to determine the dependency of adatom diffusion on strained GaN and AlN surfaces.

Type
Research Article
Copyright
Copyright © Materials Research Society 2008

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