Papers by Author: Yoshinori Hayafuji

Abstract: One of promising candidates as dopants for forming ultra-shallow and high conductive source/drain in future silicon devices has been proposed to be dimer or trimer co-dopants containing pairs or trios of different impurity elements. Making choice of a combination of the impurity elements with a small ionization energy is essential for the appropriate dimers and trimers. In this work we calculated total energies of silicon with substitutional or ineterstitial impurity elements and derived formation energies for the substitutional and interstitial impurity elements for the atomic number 1 to 83 with the exception of inert gas and lanthanum series elements. We present here the periodic table with the formation energies of the substitutional and interstitial impurity elements for determining the most stable site of the impurity elements in Si lattice. We can use this table as a database for calculating ionization energies of the impurity element.

Abstract: One of promising candidates as dopants for forming ultra-shallow and high conductive source/drain in future silicon devices has been proposed to be dimer or trimer co-dopants containing pairs or trios of different impurity elements. Making choice of a combination of the impurity elements with a small ionization energy is essential for the appropriate dimers and trimers. In this work we calculated total energies of silicon with substitutional or ineterstitial impurity elements and derived formation energies for the substitutional and interstitial impurity elements for the atomic number 1 to 83 with the exception of inert gas and lanthanum series elements. We present here the periodic table with the formation energies of the substitutional and interstitial impurity elements for determining the most stable site of the impurity elements in Si lattice. We can use this table as a database for calculating ionization energies of the impurity element.

Abstract: Electronic structures of silicon with carbon, indium, or indium-carbon dimers were calculated to investigate the interaction between indium and carbon in X center due to the indium-carbon dimers. Ab initio calculations were carried out mainly for basic Si₇₁H₆₀, C-Si₇₀H₆₀, In-Si₇₀H₆₀, and InC-Si₆₉H₆₀ clusters. The results showed that : (i) the X level was observed at E_HOMO + 0.42 eV in the InC-Si₆₉H₆₀ which was a little bit shallower than E_HOMO + 0.44 eV of the corresponding substitutional In in the In-Si₇₀H₆₀, (ii) dominant constituents of density of states of the X level were the partial densities of states of In and Si, and (iii) the X level had the antibonding nature between In and C.

Abstract: It is known that acceptor-carbon complexes have ionization energies less than those of the corresponding substitutional, separate acceptors in silicon. We present the formation mechanism for a shallower acceptor energy level called an X level that is due to an indium- carbon pair. Ab initio calculation methods were used to evaluate electronic structures and lattice relaxations of silicon with indium, carbon or a carbon-indium dimer. The results shows that the bonding interaction between the 5p orbitals of the indium atom and the 3sp orbitals of the silicon atoms bound with the indium atom mainly determines the ionization energy of the X level, and the ionic bonding interaction of the carbon atomic orbitals with the indium atomic orbitals in the X level enables the bonding interaction of the orbitals between the indium atom and the silicon atom to lower the corresponding indium acceptor level, and then to form the shallower X level.