Plasticity and optical properties of GaN under highly localized nanoindentation stress fields

Nanoscale plasticity has been studied on (0001) GaN thin films, using tips with very small radius of curvature. Cross-section transmission electron microscopy images of the nanoindentations indicate that the primary slip systems are the pyramidal {1 (1) over bar 01] < 11 (2) over bar3 > and {11 (2) over bar1] < 11 (2) over bar3 >, followed by the basal {000 (2) over bar] < 11 (2) over bar0 >. Incipient plasticity was observed to be initiated by metastable atomicscale slip events that occur as the crystal conforms to the shape of the tip. Large volumetric material displacements along the {1 (1) over bar 01] < 11 (2) over bar3 > and {11 (2) over bar2] < 11 (2) over bar3 > slip systems were observed at an average shear stress of 11 GPa. Hexagonal shaped nanoindentation impressions following the symmetry of GaN were observed, with material pile-up in the < 11 (2) over bar0 > directions. Spatially resolved cathodoluminescence images were used to correlate the microstructure with the optical properties. A large number of non-radiative defects were observed directly below the indentation. Regions under tensile stress extending from the nanoindentation along < 11 (2) over bar0 > directions were associated with the {000 (2) over bar] < 11 (2) over bar0 > slip. Published by AIP Publishing.