Nano-indentation studies were carried out on epitaxial GaN thin films on (0001) Si substrates. A single pop-in (discontinuity) in the load–indentation depth curve was observed for GaN films at depths of 23 to 26. The physical mechanism responsible for the so-calld pop-in event in these epitaxial films could be due to the interaction behavior of the indenter tip with the pre-existing threading dislocations present in the films during mechanical deformation. It was observed that the pop-in depth was dependent upon the lattice mismatch of the epitaxial thin film with the substrate: the higher the lattice mismatch, the shallower was the critical pop-in depth.

A Nanoindentation Analysis of the Influence of Lattice Mismatch on Some Wide Band Gap Semiconductor Films. R.Navamathavan, S.J.Park, J.H.Hahn, C.K.Choi: Physica B, 2008, 403[4], 675-8