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Polytypes, Silicon Carbide, Topography,
The use of synchrotron radiation source X-ray diffraction edge topography (SRS-XRDET) has been developed as a technique for investigating the spatial coalescence of polytypes in silicon carbide [1]. The problem has been of long-standing concern in materials science [2], while there is renewed interest in this burgeoning wide band gap semiconductor material. Current effort underlines the importance of understanding the role of defects and disorder in polytype formation and the novel application of SRS-XRDET is well suited to this task.
The use of SRS-XRDET to obtain polytype profiles along with quantitative information on adjacent polytype neighbours and the regions between them has highlighted the ubiquitous nature of thin one-dimensionally disordered (1DD) layers [3]. A recent detailed study of long period polytype (LPP) coalescence [4] has enabled individual layer thickness measurements of periods up to 474H to be obtained for the first time (see Fig. 1).
A significant empirical trend is reported here that relates the thickness of LPP layers to the periodicity of the repeat stacking sequence measured on the topographs. A good correlation between the data suggests that this behaviour is governed by a simple mathematical expression y = k x - n. Values for k and n have been determined that relate the polytype thickness (y in microns) to the number of hexagonal layers (x) in the polytype stacking repeat. This law appears to govern the universal behaviour of LPP coalescence in Lely grown SiC crystals.