The mechanical deformation of wurtzite-phase epilayers, grown onto sapphire substrates, was studied by spherical indentation, cross-sectional transmission electron microscopy, and scanning cathodoluminescence monochromatic imaging. The cathodoluminescence imaging of indentations which exhibited plastic deformation (on the basis of indentation data) exhibited a so-called footprint of deformation-produced defects that resulted in a strong reduction in the intensity of cathodoluminescence emissions. Multiple discontinuities were observed, during loading, when the maximum load was above the elastic-plastic threshold. This behavior could be correlated with multiple slip bands, as revealed by cross-sectional transmission electron microscopy. No sign of pressure-induced phase transformations was found from within the mechanically damaged regions by using selected-area diffraction patterns. The main deformation mechanism appeared to be the nucleation of slip on the basal planes, with dislocations being nucleated on additional planes during further loading. Cross-sectional transmission electron microscopy revealed no cracking or delamination for loads of up to 250mN.

Indentation-Induced Damage in GaN Epilayers. J.E.Bradby, S.O.Kucheyev, J.S.Williams, J.Wong-Leung, M.V.Swain, P.Munroe, G.Li, M.R.Phillips: Applied Physics Letters, 2002, 80[3], 383-5