Journal of Electron Microscopy Advance Access originally published online on August 25, 2005
Journal of Electron Microscopy 2005 54(3):243-250; doi:10.1093/jmicro/dfi033
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Compositional modulation in InxGa1xN: TEM and X-ray studies
1 Materials Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron road, Berkeley, CA 94720, USA, 2 Materials Science and Engineering, University of California, Berkeley, Berkeley, CA 94720, USA and 3 Department of Electrical and Computer Engineering, Cornell University, Ithaca, NY 14853, USA
* To whom correspondence should be addressed. E-mail: z_liliental-weber@lbl.gov
Transmission Electron Microscopy (TEM) and X-ray diffraction (XRD) have been used to study compositional modulation in InxGa1x 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
2
coupled geometry. The ordering period
measured along c-axis was about
= 45 Å for x = 0.5 and
= 66 Å for x = 0.78 for samples grown on AlN buffer layer. TEM and XRD determinations of
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
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
Received 7 January 2005, accepted 16 March 2005