CBED study of grain misorientations in AlGaN epilayers

Abstract: Large angle convergent beam electron diffraction (LACBED) has been used to examine AlGaN epilayers grown by facet-controlled epitaxial lateral overgrowth on GaN/(0001) sapphire substrates in prototype UV laser structures. The substrates, defined by masks with seed openings along a stripe direction, had GaN seed columns with surfaces. Studies were carried out on cross-sectional samples cut perpendicular to the stripe axis. An LACBED analysis of the orientation of (000 2) planes, and of the planes parallel to the stripe axis, revealed that the AlGaN wings were both rotated by angles of 1–2×10−2 radians about the stripe axis with respect to the underlying GaN, and distorted due to misfit strains. It is shown that the results are consistent with the observed structure of the AlGaN/GaN and the wing/wing boundaries, and with a new model for the generation of a-type misfit dislocations at the AlGaN/GaN interface. [Copyright &y& Elsevier]