The electronic structures and X-ray photoelectron spectra of silicon models with octahedral B 6 , icosahedral B 12 , or cubooctahedral B 12 clusters are investigated using first-principles calculations. It is found that the B 6 and B 12 clusters act as double acceptors in silicon and that the simulated chemical shift of the B 1s orbital signals of the B 6 and cubo-octahedral B 12 clusters in X-ray photoelectron spectra coincides exactly 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 and cubo-octahedral B 12 clusters are the origin of hole carriers in silicon. We propose a mechanism for hole generation and a physical model for boron cluster formation at implantation-induced divacancy sites and multi vacancy sites.
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.
Ab initio calculations of the atomic and electronic structure of crystalline silicon (c-Si) with X@B 6 and X@B 12 (X ¼ H{Br) clusters have been performed to investigate carrier generation by doping atoms inside the cage of the boron clusters. We confirmed that octahedral B 6 , cubo-octahedral B 12 (B 12 -CO) and icosahedral B 12 (B 12 -ICO) can exist stably in c-Si and should act as double acceptors. We also found that H atoms can be settled in B 12 -CO clusters and the H@B 12 -CO cluster can introduce a very shallow single acceptor level whose activation energy is lower than those of B 6 , B 12 (-CO, -ICO) and substitutional boron atom (B s ). It is found on the basis of the formation energies that B@B 6 and B@B 12 will inevitably be formed and may degrade the efficiency of carrier generation. The H@B 12 -CO cluster is one of the most promising candidates as the cluster dopant for the improvement of the efficiency of boron implantation and the formation of a high-performance extremely shallow junction.
ABSTRACT:In the field of Si nanoscale ultralarge-scale integration, the quantum confinement effect is undesirable with respect to the device characteristics and performance because the carriers are entirely confined in nanoscale or low-dimensional structures. Significant efforts are being made with regard to the positive use of the quantum confinement effect in Si nanoscale structures. One such attempt is related to the use of Si optoelectronics and photonics for optical interconnections within a Si chip. In this study, the intrinsic electronic structures in the Si-based nanostructures with different dimensions and sizes as candidates for Si optoelectronics were investigated by the DV-X␣ molecular orbital calculation, which is advantageous to simulate the valence band structures for nanomaterials. We discuss the shift of a light emission peak to a higher energy due to the quantum confinement of carriers in the Si-based nanostructures, which depends on the sizes and numbers of structural dimensions, on the basis of the calculated results. Also, effect of doping of group IIIB and VB elements in the periodic table on the extrinsic electronic structures of the Si-based nanostructures were clarified by combining the Vienna ab-initio code for determining the relaxation structures around the dopants with the DV-X␣ method for simulating the valence band structures. The results obtained are useful as a measure of possibility of the Si-based nano-structured materials for optoelectronics.
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