Nucleation Mechanism of 6H-SiC Polytype Inclusions Inside 15R-SiC Crystals YU ZHANG, 1 HUI CHEN, 1 GLORIA CHOI, 1 BALAJI RAGHOTHAMACHAR, 1 MICHAEL DUDLEY, 1,5 JAMES H. EDGAR, 2 KRZYSZTOF GRASZA, 3 EMIL TYMICKI, 3 LIHUA ZHANG, 4 DONG SU, 4 and YIMEI ZHU 4 1.—Department of Materials Science and Engineering, Stony Brook University, Stony Brook, NY, USA. 2.—Department of Chemical Engineering, Kansas State University, Manhattan, KS, USA. 3.—Institute of Electronic Materials Technology, Warsaw, Poland. 4.—Center for Functional Materials, Brookhaven National Laboratory, Upton, NY, USA. 5.—e-mail: mdudley@notes.cc. sunysb.edu A model is presented for the nucleation mechanism of 6H-SiC polytype inclusions inside 15R-SiC boules. Inhomogeneous densities of screw disloca- tions lead to uneven growth rates, resulting in complex step overgrowth processes which can partially suppress the Burgers vector of a 15R 1c screw dislocation through the creation of Frank faults and Frank partial disloca- tions. Combined with stacking shifts induced by the passage of basal plane partial dislocations, it is shown that the partial Burgers vector suppression can leave behind a residual 6H 1c dislocation, which then acts as a nucleus for reproduction of 6H-SiC structure in the 15R-SiC crystal. Key words: Polytype inclusion, polytype transformation, screw dislocation, partial dislocation INTRODUCTION Silicon carbide possesses outstanding properties such as high breakdown field, wide bandgap, high thermal conductivity, good chemical and mechani- cal stability, and high saturated electron drift velocity that constitute a significant improvement over conventional semiconductor materials for many envisaged applications. However, while some applications have already been realized, issues relating to crystalline defects and polytype inclu- sions remain a barrier to the successful realization of several others. SiC is noted for its large number of polytypes. 1 Up to now, more than 200 types of phases of SiC have been found. 2,3 Due to the variety of polytypes and the limitation of growth condition control, it is fairly common to have polytype inclusions embedded in SiC crystals, which may lead to nucleation of device-killing micropipes. 4 Consequently, the nucle- ation mechanism of polytype inclusions in SiC crystals assumes great importance. The goal of this paper is to understand the nucleation mechanism of 6H-SiC polytype inclusions inside 15R-SiC crystals, so as to design strategies to mitigate their negative effects on SiC devices by completely eliminating them. First, it is necessary to understand the stacking rules in SiC. The structure of SiC can be considered as an assembly of corner-sharing tetrahedra. 5–7 Every SiC tetrahedron arises from tetrahedral bonding between silicon and carbon atoms, and the SiC tetrahedra are joined to each other at their corners. A tetrahedron in a close-packed assembly of corner-sharing tetrahedra can occupy one of three sites on the c-plane: A, B, or C. By rotating the tetrahedron by 180° around the c-axis, we obtain a twinned tetrahedron with twinned variants A¢,B¢ or C¢. The SiC polytypes consist of various stacking permutations of these six types of tetrahedra. Corner-sharing places certain restrictions on the stacking of two tetrahedra on top of one another. 7 (Received October 1, 2009; accepted January 29, 2010; published online February 24, 2010) Journal of ELECTRONIC MATERIALS, Vol. 39, No. 6, 2010 DOI: 10.1007/s11664-010-1105-8 Ó 2010 TMS 799