Ultra-micro-indentation of silicon and compound semiconductors with spherical indenters
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Ultra-micro-indentation of silicon and compound semiconductors with spherical indenters J. S. Williams,a) Y. Chen, J. Wong-Leung, and A. Kerr Department of Electronic Materials Engineering, RSPhysSE, Australian National University, Canberra, 0200, Australia
M. V. Swain CSIRO Division of Telecommunications and Industrial Physics, Lindfield, 2070, Australia (Received 9 September 1998; accepted 12 March 1999)
Details of microindentation of silicon, such as the semiconductor-to-metal transformation, which takes place on loading, have been examined using spherical indenters. Various forms of silicon are studied, including heavily boron-doped wafers and silicon damaged and amorphized by ion implantation as well as material containing dislocations. Results indicate that only silicon, which contains high concentrations of point defects or is amorphous, exhibits mechanical properties that differ significantly from undoped, defect-free crystal. Amorphous silicon exhibits plastic flow under low indentation pressures and does not appear to undergo phase transformation on loading and unloading. Indentation of compound semiconductors is also studied and the load/unload behavior at room temperature is quite different from that of silicon. Both gallium arsenide and indium phosphide, for example, undergo slip-induced plasticity above a critical load.
I. INTRODUCTION
It is now widely recognized that silicon undergoes a series of phase transformations when subjected to high pressures, using both conventional high pressure devices, such as diamond anvils or hydrostatic pressure cells, or under indentation. For example, Hu et al.1,2 have measured the hydrostatic pressures under which particular transformations occur: diamond cubic Si, socalled Si-I, transforms to a metallic b –Sn phase at a pressure of 11 –13 GPa (Si-II), involving a 22% increase in density. At higher pressures, Si undergoes further densifications to, for example, primitive hexagonal and then hcp phases, the latter occurring at pressures of .40 GPa and involving a densification of around 35%. During unloading, Si-II undergoes an expansion to a bcc structure (Si-III) which is 8% more dense than Si-I and occurs at a pressure of 8–11 GPa. Similar behavior has been observed under indentation experiments, beginning with the early Russian work3,4 which identified, through a change in electrical resistivity, a likely semiconductorto-metallic transition during loading. More recent work by Clarke and co-workers,5–7 using pointed indenters, illustrated the Si-I to Si-II transformation on loading and a “pop-out” event on unloading, the latter suggestive of the Si-II to Si-III transformation. However, transmission electron micrographs (TEM) of the residual indentation8,9 indicated that a predominantly amorphous phase may form during rapid unloading.
a)
Address all correspondence to this author. e-mail: [email protected]
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http://journals.cambridge.org
J. Mater. Res., Vol. 14, No. 6, Jun 1999
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