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The SC16 Structure

Since the BC8 structure is characterised by even membered rings, is is possible to construct a diatomic analogue in which only unlike species are bonded. However the 8 atom body centered cell is not appropriate for this. If the BC8 structure is considered to be simple cubic with 16 atoms in the unit cell then 2 species can be arranged with only unlike species bonding. It follows that this structure has lower symmetry - primitive cubic, with point group symmetry P tex2html_wrap_inline6510 and unlike BC8 it does not have a centre of inversion. The effect of this is that the structure can be fully described by two internal parameters, tex2html_wrap_inline5298 , where s=1,2 labels the species. Curiously, the lengths of the bonds depend only on one parameter, tex2html_wrap_inline6516 . The distance to the nearest non-bonded neighbour, tex2html_wrap_inline5268 , is species dependent. These lengths can be expressed in terms of the lattice parameter and tex2html_wrap_inline5298 by

eqnarray1405

Like the BC8 structure in Group IV elements, the SC16 structure with its distorted tetrahedral units is a tractable complex crystal model of amorphous III-V semiconductors having short range disorder and zero like species bonding. Studies of the structural, optical and electronic properties of GaAs in the SC16 structure have been made using an empirical pseudopotential method in an attempt to investigate the amorphous phase[66].



Stewart Clark
Thu Oct 31 19:32:00 GMT 1996