Bradby, J. E.Kucheyev, S. O.Williams, J. S.Wong-Leung, JenniferSwain, M. V.Munroe, P.Li, G.Phillips, M. R.2015-10-202015-10-200003-6951http://hdl.handle.net/1885/15983The mechanical deformation of wurtzite GaN epilayers grown on sapphire substrates is studied by spherical indentation, cross-sectional transmission electron microscopy (XTEM), and scanning cathodoluminescence(CL) monochromatic imaging. CL imaging of indents which exhibit plastic deformation (based on indentation data) shows an observable “footprint” of deformation-produced defects that result in a strong reduction in the intensity of CL emission. Multiple discontinuities are observed during loading when the maximum load is above the elastic-plastic threshold, and such a behavior can be correlated with multiple slip bands revealed by XTEM. No evidence of pressure-induced phase transformations is found from within the mechanically damaged regions using selected-area diffraction patterns. The main deformation mechanism appears to be the nucleation of slip on the basal planes, with dislocations being nucleated on additional planes on further loading. XTEM reveals no cracking or delamination in any of the samples studied for loads of up to 250 mN.http://www.sherpa.ac.uk/romeo/issn/0003-6951..."Publishers version/PDF may be used on author's personal website, institutional website or institutional repository" from SHERPA/RoMEO site (as at 20/10/15). Copyright 2002 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Applied Physics Letters and may be found at https://doi.org/10.1063/1.1436280Keywords: Basal planes; Cross-sectional transmission electron microscopy; Damaged region; Deformation mechanism; Elastic-Plastic; GaN epilayers; Maximum load; Mechanical deformation; Monochromatic imaging; Multiple slips; Pressure-induced phase transformations; Sap2002-01-2110.1063/1.14362802016-02-24