Abstract :
Amorphous silicon–carbon alloys, with widely different proportions of silicon and carbon, can be prepared in various ways,
in particular by chemical vapour deposition (CVD) or by pyrolysis of silicated organic polymers. The literature on disordered
SiC is very abundant with an extremely wide range of reported properties. This diversity is due to the admixture, in variable
proportions, of sp3 and sp2 local structures of carbon. This is rather unfortunate because—if the sp3 structure (diamond-like)
tends indeed to give a wide gap material—the admixture of sp2 bonds (graphite-like, with a zero optical gap) results in a
material with an overall gap which is often too small for optoelectronic applications in the visible.
One notable exception is that of amorphous Si–C alloys prepared by CVD at low power. In this regime, the power
delivered to the plasma is below the threshold of primary decomposition of the CH4 precursor. Carbon is, therefore,
incorporated as methyl groups –CH3, thus forcing sp3 hybridisation in the solid. The optical gap can then reach high values,
allowing electroluminescent devices emitting visible light. However, since the Si–C network is not allowed to relax to the
more stable sp2–sp3 admixture, this material is more strained than the low-gap standard material. # 2001 Elsevier Science
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