The bonding configuration in a partially relaxed pseudomorphic epilayer of SiGe: evidence of the BC-8 phase of silicon

Abstract

The bonding configuration of a silicon host lattice in a carbon-induced partially relaxed pseudomorphic epilayer of SiGe is studied using x-ray photoelectron spectroscopy, high-resolution XRD and Raman spectroscopic techniques. In-plane and out-of-plane strains are estimated using high-resolution x-ray diffraction. Careful analysis of the x-ray photoelectron spectra (XPS) suggests that the bonding environment of the silicon host lattice is modified, and is attributed to the presence of graphite-like-sp 2 bonding in addition to the tetrahedral-sp 3 bonding. These results are further supported by our Raman studies. Our Raman studies indicate the presence of the BC-8 phase; a high-pressure phase of silicon. The modified configuration of the silicon host lattice at high pressure is responsible for the observed changes in the XPS and Raman spectra. These results are also compared with the carbon incorporated silicon epilayers (Si 1−x C x ) having negligible strain relaxation. We attribute these effects to the strain-induced effects and not to the compositional effects of Ge.

Novel silicon phases and nanostructures for solar energy conversion

“…The authors argued that pressure waves generated by the fspulses first amorphized regions of the sample and then induced the nucleation of R8 and BC8 NPs within these regions. Formation of nanocrystalline BC8 regions was also observed in nano-grinding experiments, 70 in SiGe epilayers, 71 and in nanoindentation experiments. [72][73][74][75] Recently, even direct colloidal synthesis of BC8 nanoparticles was reported, which would completely bypass the need for high pressure synthesis.…”

High-Pressure Core Structures of Si Nanoparticles for Solar Energy Conversion

“…This suggests that BC8 particles played an active role in enhancing the low energy absorption. Formation of nanocrystalline BC8 regions were also observed in nano-grinding experiments [22] and in SiGe epilayers [23].…”