Polytypism and One-Dimensional Disorder in Silicon Carbide
Jim Kelly's main scientific research interest is in Synchrotron
of polytype layers and defects in semiconductor silicon carbide.
Polytype coalescence in Lely vapour grown silicon carbide (SiC) has
now been studied
extensively using the technique of X-Ray Diffraction (XRD).
These experiments were performed on Station 7.6 of the
Daresbury Synchrotron Radiation Source
(SRS). The technique of Synchrotron
Topography (SRS-XRDT) has been used
to provide diffraction contrast from the edge rather than the more
substantial faces of the SiC crystals, with a white beam of continuous
Using this novel methodology a unique database has been built up of the spatial
distribution of one-dimensional disorder (1DD) and regions of
high defect density
< 5 mm between the adjoining common polytypes
(6H, 4H and 15R) and Long Period Polytypes (LPP's). Next nearest neighbour
relationships have prompted a model termed an
American club sandwich to be proposed by
Kelly, Barnes & Fisher.
Click here to see an example of the
"missing method ?" of assignment, to build up a depth profile of
polytypes in SiC from morphological clues on an X-ray topograph.
Check beam status at the SRS