Nanoindentation of laterally overgrown epitaxial gallium nitride

Nanoindentation has been used to investigate and compare the mechanical properties of GaN grown by the lateral epitaxial overgrowth (LEO) method and the defective seed region prepared by metalorganic chemical vapour deposition. Common modulus of elasticity values (∼230 GPa) and hardness values (∼19 GPa) were found for both materials. The GaN response to nanoindentation was found to be purely elastic for low indentation loads with the onset of plasticity being marked by discontinuities or “pop-in” events in the indenter load-penetration curves. The maximum shear stress under the indenter at pop-in events for LEO GaN corresponds well with the critical shear stress necessary for homogeneous dislocation nucleation, indicating that the defects in this region are too sparse and do not aid in dislocation nucleation.