Direct Observation of Stacking Fault Nucleation from Deflected Threading Dislocations with Burgers Vector c+a in PVT Gro
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Direct Observation of Stacking Fault Nucleation from Deflected Threading Dislocations with Burgers Vector c+a in PVT Grown 4H-SiC Fangzhen Wu1, Huanhuan Wang1, Balaji Raghothamachar1 and Michael Dudley1,a, Stephan G. Mueller2, Gil Chung2, Edward K. Sanchez2, Darren Hansen2, and Mark J. Loboda2 1 Department of Materials Science and Engineering, Stony Brook University, Stony Brook, NY, 11790, U.S.A. 2 Dow Corning Compound Semiconductor Solutions, Midland, Michigan, 48686, U.S.A. a [email protected] ABSTRACT In our previous studies [1-3], four kinds of stacking faults in 4H-SiC bulk crystal have been distinguished based on their contrast behavior differences in synchrotron white beam x-ray topography images. These faults are Shockley faults, Frank faults, Shockley plus c/2 Frank faults, and Shockley plus c/4 Frank faults. Our proposed formation mechanisms for these stacking faults involve the overgrowth of the surface outcrop associated with threading screw dislocations (TSDs) or threading mixed dislocations (TMDs) with Burgers vector of c+a by macrosteps and the consequent deflection of TSDs or TMDs onto the basal plane. Previous synchrotron x-ray topography observations were made in offcut basal wafers using transmission geometry. In this paper, further evidence is reported to confirm the proposed stacking fault formation mechanism. Observations are made in axially cut slices with surface plane {11-20}. Several kinds of stacking faults are recognized and their contrast behavior agrees with the four kinds previously reported. Direct observation is obtained of a Shockley plus c/4 Frank stacking fault nucleating from a TMD deflected onto the basal plane. The contrast from stacking faults on the basal plane in the axial slices is enhanced by recording images after rotating the crystal about the active -1010 reflection vector enabling a broader projection of the basal plane. INTRODUCTION 4H-SiC is a promising material to substitute for silicon in next generation power devices capable of operation under severe conditions such as high temperature, high blocking voltage, and high frequency switching [4]. High quality 4H-SiC crystals are required to make substrate wafers and are currently grown using physical vapor transport technique (PVT). In the past decade, defect densities in 4H-SiC have been dramatically reduced. For example, micropipes have been practically eliminated [5], while TSD and BPD densities have decreased by orders of magnitude down to several hundred and several thousand per square centimeter respectively. Stacking faults in the substrates have gained some attention recently and in our previous work four kinds of stacking faults have been reported in terms of their fault vectors, e.g. Shockley faults, Frank faults, Shockley plus c/2 Frank faults, and Shockley plus c/4 Frank faults [1-3]. Generally speaking, defects reaching the growth surface will extend into the epi layer and may potentially harm the performance of devices grown on it. Understanding the formation mechanism of stacking faults may
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