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Title: Structural anisotropic properties of a-plane GaN epilayers grown on r-plane sapphire by molecular beam epitaxy

Heteroepitaxial non-polar III-Nitride layers may exhibit extensive anisotropy in the surface morphology and the epilayer microstructure along distinct in-plane directions. The structural anisotropy, evidenced by the “M”-shape dependence of the (112{sup ¯}0) x-ray rocking curve widths on the beam azimuth angle, was studied by combining transmission electron microscopy observations, Raman spectroscopy, high resolution x-ray diffraction, and atomic force microscopy in a-plane GaN epilayers grown on r-plane sapphire substrates by plasma-assisted molecular beam epitaxy (PAMBE). The structural anisotropic behavior was attributed quantitatively to the high dislocation densities, particularly the Frank-Shockley partial dislocations that delimit the I{sub 1} intrinsic basal stacking faults, and to the concomitant plastic strain relaxation. On the other hand, isotropic samples exhibited lower dislocation densities and a biaxial residual stress state. For PAMBE growth, the anisotropy was correlated to N-rich (or Ga-poor) conditions on the surface during growth, that result in formation of asymmetric a-plane GaN grains elongated along the c-axis. Such conditions enhance the anisotropy of gallium diffusion on the surface and reduce the GaN nucleation rate.
Authors:
; ; ; ; ; ;  [1] ; ; ;  [2] ;  [3]
  1. Physics Department, Aristotle University of Thessaloniki, 54124 Thessaloniki (Greece)
  2. Department of Physics, Microelectronics Research Group, University of Crete, P.O. Box 2208, GR 71003, Greece and IESL, FORTH, P.O. Box 1385, GR71110 Heraklion (Greece)
  3. Physics Division, School of Technology, Aristotle University of Thessaloniki, GR54124 Thessaloniki (Greece)
Publication Date:
OSTI Identifier:
22304248
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 115; Journal Issue: 21; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; ANISOTROPY; ASYMMETRY; ATOMIC FORCE MICROSCOPY; DIFFUSION; DISLOCATIONS; GALLIUM NITRIDES; MICROSTRUCTURE; MOLECULAR BEAM EPITAXY; RAMAN SPECTROSCOPY; RELAXATION; RESIDUAL STRESSES; RESOLUTION; SAPPHIRE; SPACE DEPENDENCE; SUBSTRATES; SURFACES; TRANSMISSION ELECTRON MICROSCOPY; X-RAY DIFFRACTION