Direct Determination of Burgers Vectors of Threading Mixed Dislocations in 4H-SiC c-Plane Wafers Grown by PVT Method

Threading Screw Dislocations (TSDs) have long been observed in 4H-SiC crystals grown by the Physical Vapor Transport (PVT) method. Recent studies [1] show that a significant proportion of these threading dislocations are actually mixed type dislocations with a Burgers vectors nc+ma (where n and m are integers). With the help of Synchrotron White Beam X-ray Topography, it is straightforward to distinguish these mixed type threading dislocations from pure screw dislocations simply by recording different reflections from an axially cut sample (cut parallel to growth direction) and applying the g.b=0 and g.bxl=0 invisibility criteria (g – diffraction vector;  b – Burgers vector). However, axial wafers are only cut from the boules slated for research purposes and are usually unavailable for boules from which commercially preferred c-plane oriented wafers are sliced. In this study, Synchrotron Monochromatic X-ray topography was carried out on a 100mm 4H-SiC c-cut commercial wafer and contrast variation was observed for each single threading screw or mixed dislocation image on six different types of 11-28 reflections. The way the contrast varied in the different reflections was also found to be different and actually depends on the nature of the dislocation itself. Ray Tracing Simulation was then carried out to confirm this observation. This simulation method is capable of simulating dislocation contrast in various geometries and it is based on the fact that orientation contrast is the predominant contributor to contrast from threading dislocations in the grazing incidence and back reflection geometries. According to the simulation results and their comparison to the observed contrast, it is in principle possible to determine the Burgers vector of any single threading dislocation using this methodology.

[1] F. Wu, H. Wang, S. Byrappa, B. Raghothamachar, M. Dudley, E. K. Sanchez, D. Hansen, R. Drachev, S. G. Mueller, and M. J. Loboda, Mater. Sci. Forum 717-720, 343(2011).

[2] X. R. Huang, M. Dudley, W. M. Vetter, W. Huang, W. Si, and C. H. Carter, Jr., J. Appl. Cryst. 32, 516 (1999).