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

Abstract

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 {11¯01}⟨112¯3⟩ and {112¯2}⟨112¯3⟩, followed by the basal {0002}⟨112¯0⟩. Incipient plasticity was observed to be initiated by metastable atomic-scale slip events that occur as the crystal conforms to the shape of the tip. Large volumetric material displacements along the {11¯01}⟨112¯3⟩ and {112¯2}⟨112¯3⟩ 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 ⟨112¯0⟩ 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 ⟨112¯0⟩ directions were associated with the {0002}⟨112¯0⟩ slip.

Estimations of Low Temperature Dislocation Mobility in GaN

“…These half‐loops expand in the slip planes intersecting the surface. Although CL experiments do not allow to determine directly the acting slip system, the most of transmission electron microscopy investigations led to conclusion that the dislocations glide in the {1 01} and {11 2} pyramidal planes . Dislocation glide in the basal plane was also revealed in the previous investigations, however, as seen in Figure , the basal dislocation loops are not revealed in the studied films due probably to rather high density of threading dislocations, which can pin the basal dislocation propagation …”

“…Thus, the detailed knowledge of the dislocation dynamic properties is essentially important for the control of dislocation generation and multiplication during crystal growth and device processing. The mechanical properties of GaN were mainly studied by the nanoindentation measurements that allowed estimation of Young's modulus and hardness values . On the load‐penetration curves measured at room temperature, the pop‐in events were revealed practically in all measurements and they were explained by the plastic deformation under the indentation.…”

“…On the load‐penetration curves measured at room temperature, the pop‐in events were revealed practically in all measurements and they were explained by the plastic deformation under the indentation. The dislocations introduced by indentation at room temperature were directly revealed by chemical etching, cathodoluminescence (CL), and electron beam induced current (EBIC) methods …”

Estimate of theoretical shear strength of C60 single crystal by nanoindentation

“…The phenomenon of pop-in is well studied for fcc [16,17], bcc [18] and hcp [19] metals, refractory materials (oxides [20,21], borides [22,23], nitrides [9,24], carbides [25]), semiconductors [26] and ionic crystals [27]. However, the pop-in response of molecular single crystals remains poorly investigated [28].…”

The Indentation-Induced Pop-in Phenomenon and Fracture Behaviors of GaP(100) Single-Crystal

“…In some cases, it has been also interpreted as the manifestations of the dislocation activity [18,19,20] depending strongly on the crystal structure of the test materials [25], temperature [26], the shape of indenter tip [27] and indenter angle [28]. Furthermore, the correlations between pop-in behaviors and dislocation activities of materials have been widely studied by combining microstructural observations with the cross-sectional transmission electron microscopy in recent years [29,30,31].…”