Cyclic nanoindentation and Raman microspectroscopy study of phase transformations in semiconductors

This paper supplies new interpretation of nanoindentation data for silicon, germanium, and gallium arsenide based on Raman microanalysis of indentations. For the first time, Raman microspectroscopy analysis of semiconductors within nanoindentations is reported. The given analysis of the load-displacement curves shows that depth-sensing indentation can be used as a tool for identification of pressure-induced phase transformations. Volume change upon reverse phase transformation of metallic phases results either in a pop-out (or a kink-back) or in a slope change (elbow) of the unloading part of the load-displacement curve. Broad and asymmetric hysteresis loops of changing width, as well as changing slope of the elastic part of the loading curve in cyclic indentation can be used for confirmation of a phase transformation during indentation. Metallization pressure can be determined as average contact pressure (Meyer's hardness) for the yield point on the loading part of the load-displacement curve. The pressure of the reverse transformation of the metallic phase can be measured from pop-out or elbow on the unloading part of the diagram. For materials with phase transformations less pronounced than in Si, replotting of the load-displacement curves as average contact pressure versus relative indentation depth is required to determine the transformation pressures and/or improve the accuracy of data interpretation.