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GaN Quantum Dots Grown at High Temperatures by Molecular Beam Epitaxy

Published online by Cambridge University Press:  01 February 2011

Tao Xu ,
Adrian Williams ,
Christos Thomidis ,
Theodore D. Moustakas ,
Lin Zhou  and
David J. Smith
Tao Xu
Affiliation:
Dept. of Electrical and Computer Engineering, Boston University, Boston, MA
Adrian Williams
Affiliation:
Dept. of Electrical and Computer Engineering, Boston University, Boston, MA
Christos Thomidis
Affiliation:
Dept. of Electrical and Computer Engineering, Boston University, Boston, MA
Theodore D. Moustakas
Affiliation:
Dept. of Electrical and Computer Engineering, Boston University, Boston, MA
Lin Zhou
Affiliation:
Dept. of Physics and Astronomy and Center for Solid State Science, Arizona State University, Tempe, AZ
David J. Smith
Affiliation:
Dept. of Physics and Astronomy and Center for Solid State Science, Arizona State University, Tempe, AZ
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Abstract

In this paper we report the growth by MBE of GaN quantum dot superlattices (QDSLs) with AlN barriers on (0001) sapphire substrates at relatively high temperatures (770 °C) by the modified Stranski-Krastanov method. TEM studies indicate that the GaN QDs are truncated pyramids. We find that the height distribution of the dots depends strongly on the number of GaN monolayer coverage on the top of AlN. Specifically, we find that the height distribution consists of two Gaussian distributions (bimodal) for coverage of 3 and 4 MLs, and becomes single Gaussian distribution for 5 and 6 MLs of coverage. Furthermore, we find that the density of quantum dots increases with the degree of coverage and saturates at 2×1011 dots/cm2. The number of stacks in the superlattice structure was also found to lead to bimodal height distribution of the QDs. Ordering of the quantum dots was accomplished by thermal annealing of the sapphire substrates at 1400 °C prior to the growth of GaN QDs. The annealing process reveals the vicinal steps due to the miscut of the substrates and the GaN QDs were found to line up along those steps. Photoluminescence studies show a broad luminescence spectrum centered at 3 eV which is red shifted with respect to that of bulk GaN and is consistent with internal fields due to polarization (Quantum Confined Stark Effect). Furthermore, we find that the luminescence intensity increases with the number of stacks in the superlattice structure due to higher spatial density of QDs.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 831: Symposium E – GaN, AlN, InN, and Their Alloys , 2004 , E2.4
Copyright
Copyright © Materials Research Society 2005

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References

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