Defects Self-Organization in a Free Standing Buckled GaN Film From 3D Laue X-ray Microdiffraction

A novel white-beam microdiffraction analysis of defects, strains and tilts in a free standing $m$-plane GaN film grown via hydride vapor phase epitaxy is presented. Depth-resolved measurements reveal dilatational strain gradient along the film normal and formation of large 3D stress fields. It is shown that misfit dislocations self-organize within cell boundaries creating local lattice rotations between the growing cells. Growth cells are highly misoriented relative to each other. Misorientation angle fluctuates in the range of 1.5 - 4.5 degrees. Distribution of lattice rotations in the film is not homogeneous. Regions of large rotations are separated by low rotations regions. The dominating rotation axis is parallel [11-20] direction. There is little overall lattice rotation around the [0001] axis. In contrast the maximal in plane shear stress component is observed along [0001]. Research supported by the Division of Materials Sciences and Engineering, U.S. Department of Energy. Use of the APS supported by Division of Scientific Users Facilities, U.S. D.O. E.