Transition Temperatures in Plastic Yielding and Fracture of Semiconductors
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P. PIROUZ
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L. P. KUBIN , J. L. DEMENET , M. H. HONG
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A. V. SAMANT
IDepartment of Materials Science and Engineering, Case Western Reserve University, Cleveland, OH, 44106-7204, U.S.A.. I LEM, CNRS-ONERA, B.P. 72, Av. de la Division Leclerc, 92322 Chatillon Cedex, France. 3 LMP, CNRS, SP2MI, Bd 3, Teleport 2, BP 179, 86960 Futuroscope Cedex, France ABSTRACT Recent experiments on deformation of semiconductors show an abrupt change in the variation of the critical resolved shear stress, zT, with temperature, T. This implies a change in the deformation mechanism at a critical temperature T,. In the cases examined so far in our laboratory and elsewhere, this critical temperature appears to coincide approximately with the brittle-ductile transition temperature, TBDT. In this paper, the deformation experiments performed on the wide bandgap semiconductor, 4H-SiC, over a range of temperatures and strain rates are described together with the characterization of induced dislocations below and above T by transmission electron microscopy. Based on these results, and those of Suzuki and coworkers on other compound semiconductors, some understanding of the different mechanisms operating at low and high temperatures in tetrahedrally coordinated materials has been gained, and a new model for their brittle-ductile transition has been proposed. INTRODUCTION Recently, it has been possible to perform deformation experiments on a few (six) different compound semiconductors extending the deformation temperature to regions in which they are brittle. Specifically, Suzuki and coworkers have deformed InP, InSb, GaAs, and GaP using compression tests under hydrostatic pressure in order to prevent fracture of the deformation samples before they plastically yield [1-41. Some low-temperature tests on GaAs under roughly the same conditions were actually performed some years ago by Rabier and coworkers [5,6J. In our deformation tests, Samant [7] investigated the plastic behavior of two wide bandgap semiconductors, 4H-SiC and 6H-SiC, by compression over a wide range of temperature', and strain rates. It should be mentioned that because single crystals of these two semiconductors were not available until recently, prior to the work of Samant, there were only a few reports of deformation tests on single crystal 6H-SiC and practically none on 4H-SiC. Some significant works that existed were reports by Fujita et al. [8] on compression experiments on Achesongrown crystals over the temperature range 1300-1600'C, and creep tests on Cree-grown 6H-SiC by Corman [9]. In Samant's experiments, the rather high initial density of dislocations in the samples (-103-1 0 cm-2 ), careful alignment of the sample in the deformation jig, together with the use of very low strain rates, made it possible to deform the materials at temperatures hundreds of degrees below their usual range of BDT. The results of these experiments have been reported in Refs. [7,10,11]. More recently, Demenet repeated Samant's experiments on 4H-SiC (grown at Cree Research, Inc.) obta
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