Direct determination of dislocation sense of closed-core threading screw dislocations using synchrotron white beam x-ray topography in 4H silicon carbide

Grazing-incidence synchrotron white beam x-ray topography images of closed-core threading screw dislocations in 4H silicon carbide appear as roughly elliptically shaped white features, with an asymmetric perimeter of dark contrast which is greatly enhanced on one side or other of the g vector. Ray-tracing simulations indicate that the relative position of the enhanced dark contrast feature reveals the sense of the closed-core screw dislocation. Dislocation senses so obtained were validated using back-reflection images recorded with small Bragg angle. Therefore, the sense of the closed-core threading screw dislocations can be unambiguously revealed using either grazing-incidence or "small Bragg angle" back-reflection synchrotron white beam x-ray topography. (C) 2007 American Institute of Physics.