Materials Science Forum Vols. 433-436 (2003) pp. 297-300 online at http://www.scientific.net © 2003 Trans Tech Publications, Switzerland Dynamics of 4H-SiC Plasticity S.Yu. Karpov 1 , A.V. Kulik 1 , M.S. Ramm 1 , and Yu.N. Makarov 2 1 Soft-Impact, Ltd., P.O. Box 33, 194156 St.Petersburg, Russia; e-mail: ramm@softimpact.ru 2 STR, Inc., P.O.Box 70604, Richmond, VA 23255-0604, USA; e-mail: yuri.makarov@pp.kolumbus.fi Keywords : 4H-SiC, plasticity, dislocations, yield stress, loading tests Abstract. We suggest a simplified analytical model of SiC plasticity involving both multiplication of gliding dislocations and their generation in the crystal bulk. A unified set of model parameters is determined for 4H-SiC and a correlation between the multiplication factor and the critical resolved shear stress is found by comparing the theoretical predictions with the reported data on uniaxial loading of the bulk crystals. The model is workable in a wide range of temperature and strain rate variation. Introduction Silicon carbide (SiC) is an advanced semiconductor material widely used in high-power, high- temperature electronics and as a substrate for nitride-based opto- and microelectronic devices. Up to now, the quality of the material is limited by structure defects – dislocations, micropipes, stacking faults, etc., most of which are due to plastic relaxation of the thermoelastic stress, arising during SiC crystal growth [1]. At the moment, the mechanisms of SiC plasticity are poorly understood [2- 6]. The experiments on constant-strain-rate uniaxial compression of both 6H- and 4H-SiC [3,4] have shown that a Hookian linear dependence of the resolved shear stress upon strain is sharply changed by a close-to-linear behavior when a critical resolved shear stress (hereafter, yield stress) is approached. Such a tendency implies an avalanche generation of gliding dislocation near the critical stress followed by gradual hardening of the crystal due to multiplication of the dislocations. Conventionally, the dislocation dynamics in the covalent semiconductors is considered in terms of the Alexander-Haasen (AH) model [7,8]. The only AH parameter reported for SiC to date, the activation energy of plasticity, exhibits a complex dependence upon experimental conditions. In particular, to fit the dependence of the yield stress on the strain rate and temperature, the authors of [3,4] suggested that the activation enthalpy of dislocation gliding is a function of the applied stress either directl or via activation volume. Our attempts to find the AH parameters consistent with the reported observations were failed indicating that additional mechanisms are involved in the dislocation dynamics compared to those accounted for in the conventional AH model. In this paper, we suggest a simplified analytical approach capable of describing the 4H-SiC plasticity within a unified set of parameters valid in a wide range of temperatures and strain rates. In contrast to [4], we do not distinguish here between low-temperature and high-temperature conditions. The underlying mechanisms and still open questions are also discussed, aimed at stimulating further experimental studies of SiC dislocation dynamics. Model and results Consider a uniform dislocation-mediated plastic deformation of a SiC crystal initiated by constant- strain-rate uniaxial loading, in accordance with the experimental conditions of Ref.[4]. The