Cyclic nanoindentation and Raman microspectroscopy study of phase transformations in semiconductors
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Sergey N. Dub Institute for Superhard Materials, 2 Avtozavodskaya St., Kiev 254074, Ukraine
Andreas Kailer a) and Klaus G. Nickel Universita¨t Tu¨bingen, Institut fu¨r Mineralogie, Petrologie und Geochemie, Wilhelmstr. 56, D-72074 Tu¨bingen, Germany (Received 7 December 1998; accepted 1 February 2000)
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 loaddisplacement curves as average contact pressure versus relative indentation depth is required to determine the transformation pressures and/or improve the accuracy of data interpretation. I. INTRODUCTION
It is known that the indentation of materials creates high stresses (hydrostatic and deviatoric) under diamond indenters that can cause pressure-induced phase transformations.1–6 It has also been shown that the hardness correlates with metallization pressures for a number of semiconductors.7 The conditions for phase transformation are complex, involving numerous parameters such as the shape of indenter, maximum load, loading rate, and temperature. Understanding of the mechanism of the processes under sharp indenters is of tremendous importance for interpretation of indentation data. All previous depth-sensing indentation studies conducted on Si, Ge, and GaAs showed that only silicon displays a characteristic pop-out event on pressure re-
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Present address: Fraunhofer-Institut fu¨r Werkstoffmechanik (Fh-IWM), Wo¨hlerstr. 11, D-79108 Freiburg, Germany. J. Mater. Res., Vol. 15, No. 4, Apr 2000
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lease.8 Metallization of Si and Ge during nanoindentation has been confirmed from conductivity measurements.5 Scanning electron microscope (SEM) images of nanoindentations in Si4 and Ge8 revealed an extruded layer within the contact area after indentation and provided evidence of similarity of the metallization processes in indentation of Si and Ge.9 T
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