Mechanical deformation induced in Si and GaN under Berkovich nanoindentation

Details of Berkovich nanoindentation-induced mechanical deformation mechanisms of single-crystal Si( 100) and the metal-organic chemical-vapor deposition ( MOCVD) derived GaN thin films have been systematic investigated by means of micro-Raman spectroscopy and cross-sectional transmission electron microscopy ( XTEM) techniques. The XTEM samples were prepared by using focused ion beam ( FIB) milling to accurately position the cross-section of the nanoindented area. The behaviors of the discontinuities displayed in the loading and unloading segments of the load-displacement curves of Si and GaN thin films performed with a Berkovich diamond indenter tip were explained by the observed microstructure features obtained from XTEM analyses. According to the observations of micro-Raman and XTEM, the nanoindentation-induced mechanical deformation is due primarily to the generation and propagation of dislocations gliding along the pyramidal and basal planes specific to the hexagonal structure of GaN thin films rather than by indentation-induced phase transformations displayed in Si.