Analysis of onset of dislocation nucleation during nanoindentation and nanoscratching of InP
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Christophe Ballif Ecole Polytechnique Fédérale de Lausanne (EPFL), Institute of Microengineering (IMT), Photovoltaics and Thin Film Electronics Laboratory, CH-2000 Neuchâtel, Switzerland (Received 9 June 2011; accepted 22 August 2011)
Nanoindentation and nanoscratching of an indium phosphide (InP) semiconductor surface was investigated via contact mechanics. Plastic deformation in InP is known to be caused by the nucleation, propagation, and multiplication of dislocations. Using selective electrochemical dissolution, which reveals dislocations at the semiconductor surface, the load needed to create the first dislocations in indentation and scratching can be determined. The experimental results showed that the load threshold to generate the first dislocations is twice lower in scratching compared to indentation. By modeling the elastic stress fields using contact mechanics based on Hertz’s theory, the results during scratching can be related to the friction between the surface and the tip. Moreover, Hertz’s model suggests that dislocations nucleate firstly at the surface and then propagate inside the bulk. The dislocation nucleation process explains the pop-in event which is characterized by a sudden extension of the indenter inside the surface during loading.
I. INTRODUCTION
Indentation testing is a widely recognized method to investigate the fundamental mechanical materials properties, such as the hardness, Young’s modulus, and/or Poisson’s ratio.1 This method has many other potential applications in diverse fields, e.g., investigation of phase transformations,2,3 thin film delamination,4 and/or cleavage of materials.5,6 Thus, indentation mechanics is extensively described in several text books.7,8 Most scientists agree that, in III-V semiconductors, the nucleation of dislocations, also called the elastic–plastic transition, is associated with the pop-in in the load–displacement curve in nanoindentation.9–12 Some authors13,14 found that, for InP, pop-in event is statistical and is related to a low density of native defects. The fact that plastic deformation can occur even without pop-in was explained via the difference in doping that dramatically changes the pathway to plastic deformation.14 In contrast, Almeida et al.15 found that the native oxide on InP epitaxial layer grown on semi-insulating InP (001) wafers leads to an overestimation of the mean contact pressure required for the initial plastic deformation. Mann and Pethica16,17 showed that, for GaAs, the approach velocity and the nanometric-size surface asperities play a vital role on the initial contact stiffness and the yield point. Hence, taking a)
Address all correspondence to this author. e-mail: [email protected] b) These authors have contributed equally to this work. DOI: 10.1557/jmr.2011.305 320
J. Mater. Res., Vol. 27, No. 1, Jan 14, 2012
http://journals.cambridge.org
Downloaded: 04 Apr 2015
into account nanometric surface inhomogeneities and small impact during the initial contact, some dislocation lines may be generated even at loads close to
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