The deformation processes in 4H-SiC crystals are of particular interest because they generate mostly basal plane dislocations (BPDs) which are implicated in the degradation or premature breakdown of SiC power devices [1]. Fundamental understanding of the generation and multiplication of BPDs is critical for design of growth strategies to control the density of BPDs during PVT growth of 4H-SiC crystals. Recently, we reported on the direct observation of thermal gradient induced motion of BPDs through in-situ synchrotron X-ray topography imaging of PVT-grown 4H-SiC wafers subject to high temperature treatment [2]. The multiplication of BPDs by the operation and interactions of multiple Frank-Read sources leading to formation of complex configurations was reported. We have analyzed the series of images recorded during the in-situ experiment in detail to deduce the Burgers vectors and core structures of the moving dislocation segments and measure their individual velocities. Dislocations with Burgers vector along the off-cut 11-20 direction were found to be the only dislocations undergoing deformation during heat treatment. Sample was imaged after heat treatment and the segments of dislocations used for velocity measurements were found to be either pure screw or 60° dislocations comprised of Si cores. Using the kink-diffusion model, the activation energies for dislocation motion have been estimated from the velocity data for each of these dislocation types and found to be 2.21 eV for 60° and 3.28eV for pure screw segments respectively. These values are in good agreement with the macroscopic studies of yielding of semiconductor crystals during high temperature compression and indentation experiments [3,4]. Quantitative expression of the temperature dependent critical resolved shear stress required for dislocation motion has been derived from this analysis.

References:

[1] Lendenmann, F. Dahlquist, N. Johansson, R. Soderholm, P. A. Nilsson, J. P. Bergman, and P. Skytt, Mater. Sci. Forum 353-356, 727 (2001)

[2] Yu Yang, Jianqiu Guo, Balaji Raghothamachar, Michael Dudley, Swetlana Weit, Andreas N. Danilewsky, Patrick J. McNally, Brian K. Tanner, Mater. Sci. Forum, 924, 172-175 (2018)

[3] V. Samant, P. Pirouz, Int. J. Refractory Metals and Hard Materials 16.4-6 (1998).

[4] J-L. Demenet, M. H. Hong, P. Pirouz, Scr. Mater., 43, 865-870 (2000).