A mechanism for hole generation by octahedral B6 clusters in silicon

Abstract

The electronic structure and x-ray photoelectron spectra of silicon with octahedral B 6 clusters are investigated using first-principles calculations. It is found that the B 6 clusters act as double acceptors in silicon and that the simulated chemical shift of the B 1s orbital signals of the B 6 clusters in x-ray photoelectron spectra coincides with the chemical shift of B 1s experimentally observed in as-implanted silicon at an extremely high dose of boron. These results reveal that the B 6 clusters are the origin of hole carries. We propose a mechanism of hole generation and a model of B 6 cluster formation at implantation-induced divacancy sites.

Boron Clusters in High-Dose Implanted Silicon

“…For the above reasons, we are the first to suggest, on the basis of our first-principles calculations, that octahedral B 6 clusters, which may form in divacancy V 2 sites, act as a more reasonable source of carriers than B 12 clusters. 13) In our study, we showed that a B 6 cluster in a silicon crystal introduced a shallow double acceptor level in a certain region of the energy gap and that the calculated X-ray photoelectron spectroscopy (XPS) spectra for the B 6 cluster in silicon coincided with those obtained experimentally in high dose boron-implanted silicon to verify the growth of the B 6 cluster.…”

Thermochemical Parameters and Growth Mechanism of the Boron-Doped Silicon Clusters, SinBq with n = 1–10 and q = −1, 0, +1

“…Boron is the most important element widely used to date as a p-type dopant in crystalline silicon. Earlier studies showed that when the concentration of boron is increased, formation of either a silicon boride phase or Si–B clusters occurs in crystalline Si. , These solid materials are also known for their mechanical hardness. However, despite the demonstrated importance of the boron–silicon compounds, an understanding of their electronic and thermodynamic properties is still very limited.…”

Theoretical Study of the Stability of X@B6 and X@B12 Clusters: X=H–Br in Crystalline Silicon

“…The value obtained is relatively high as the dopant for c-Si. However, considering the electron-withdrawing character of the octahedral B 6 cluster caused by its three-center bonding, 16) it is conceivable that the B 6 cluster can generate holes and play a role in the formation of the low-resistivity layers in the relatively low-dose region, as reported by Ohmori et al 5) In contrast, B@B 6 Si 108 H 114 has many mid-gap levels that are localized to the B@B 6 cluster and may act as recombination centers, and work as carrier inhibitors, reducing the conductivity. The meaning of the symbols is the same as that in Fig.…”

“…In Fig. 12, we plot experimental data on sheet carrier concentration against boron dose in as-implanted samples with a high-dose ion Figure 12 also schematizes the relation between the boron dose and the structures of the dominant boron cluster proposed by Ohmori et al 5) It can be seen that the trends vary depending on the degree of the boron dose and that it is insufficient to describe the phenomena purely in terms of the B 12 -ICO cluster, 1,2) or the B 6 and B 12 -CO clusters 5) alone. Thus, we propose the following new description of the phenomena in terms of B 7 and B 13 as well as B 6 , B 12 -CO and B 12 -ICO clusters.…”

“…Meanwhile, Okamoto et al 4) concluded that the B 12 -CO cluster was more suitable in the silicon crystalline lattice because of its symmetry adaptation. Recently, Ohmori et al 5) proposed an attractive new model for cluster formation, which stated that in the relatively low-dose region [ð1{ 3Þ Â 10 16 cm À2 ], octahedral B 6 clusters were generated and acted as double acceptors, while in the higher dose region (>3 Â 10 16 cm À2 ), this function was fulfilled by B 12 -CO clusters instead. In any case, boron clusters that can produce highcarrier-concentration layers without any post-annealing are sure to contribute to the advancement of silicon LSI technology.…”