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Journal of Electron Microscopy Advance Access published online on August 25, 2005
Journal of Electron Microscopy, doi:10.1093/jmicro/dfi033
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© The Author 2005. Published by Oxford University Press on behalf of Japanese Society of Microscopy. All rights reserved. For Permissions, please email: journals.permissions@oupjournals.org
Received January 7, 2005
Accepted March 16, 2005

Article

Compositional modulation in InxGa1-xN: TEM and X-ray studies

Zuzanna Liliental-Weber 1*, Dmitri N. Zakharov 1, Kin M. Yu 1, Joel W. Ager III1, Wladyslaw Walukiewicz 1, Eugene E. Haller 2, Hai Lu 3, and William J. Schaff 3

1 Materials Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron road, Berkeley, CA 94720, USA
2 Materials Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron road, Berkeley, CA 94720, USA; Materials Science and Engineering, University of California, Berkeley, Berkeley, CA 94720, USA
3 Department of Electrical and Computer Engineering, Cornell University, Ithaca, NY 14853, USA

* To whom correspondence should be addressed.
Zuzanna Liliental-Weber, E-mail: z_liliental-weber{at}lbl.gov


  Abstract

Transmission Electron Microscopy (TEM) and X-ray diffraction (XRD) have been used to study compositional modulation in InxGa1-x N layers grown with compositions close to miscibility gap. The samples (0.34 < x < 0.8) were deposited by molecular beam epitaxy using either a 200 nm thick AlN or GaN buffer layer grown on a sapphire substrate. Periodic compositional modulation leads to extra electron diffraction spots and satellite reflections in XRD in the {theta}-2{theta} coupled geometry. The ordering period {Delta} measured along c-axis was about {Delta} = 45 Å for x = 0.5 and {Delta} = 66 Å for x = 0.78 for samples grown on AlN buffer layer. TEM and XRD determinations of {Delta} were in good agreement. Compositional modulation was not observed for the sample with x = 0.34 grown on a GaN buffer layer. Larger values of {Delta} were observed for layers with higher In content and for those having larger mismatch with the underlying AlN buffer layer. The possibility that the roughness of the AlN growth surface promotes strong In segregation on particular crystallographic planes leading to compositional modulation is considered.

Keywords: compositional modulation; modulation period; InGaN; TEM; electron diffraction; X-ray; Z-contrast.
Dedicated to the memory of the late John M. Cowley.
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