Solid solutions of silicon in boron-carbide-type crystals

Abstract

The optical absorption spectrum of silicon-doped boron carbide in the spectral range of the absorption edge and its low-energy tail, obtained from transmission measurements between 0.25 and 4 eV, is compared with that of undoped boron carbide (B 4.3C) with comparably low distortions. Silicon is proved to be an effective dopant of boron carbide, because the edge absorption spectrum and the plasma edge are considerably changed. However, the conduction remains p-type for the sample investigated. The IR phonon spectrum of silicon-doped boron carbide is similar to that of boron-rich boron carbide, which contains a considerable amount of chainless unit cells. It is shown that the Si atoms occupy these cells, forming a two-atom chain. From a comparison of the Raman spectrum with those of similar structures and theoretical calculations, it can be estimated that the force field constant in such chains varies linearly with the distance between the atoms.