Papers by Keyword: VASP Code

Abstract: The total energies of 4H-SiC with donor-acceptor-donor (D₂A) trimer codopants (D = N, P, As, and Sb, A = B, Al, Ga, and In), the formation energies of D₂A, DA, D, and A species and the binding energies were studied using ab initio calculations in order to determine the stable structures of D₂A trimer codopants in 4H-SiC. The results of the calculations indicated that some of the trimer codopants were formed and were stable in 4H-SiC. In particular, N₂Al, N₂Ga and N₂In trimer codopants with N(C_h)-Al/Ga/In (Si_k)-N(C_h) configuration and As₂B trimer codopants with As (Si_h)-B(C_k)-As (Si_h) configuration stably exist in 4H-SiC under the doping condition wherein the concentration ratio of donors to acceptors is 2 : 1.

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: 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.

Abstract: The total energies of donor-acceptor-donor D₂A trimer codopants (D = As and Sb, A = B, Al, Ga, In and Tl) in Si and their electronic geometrically stable structures were studied using ab initio calculations in order to propose new dopants for the formation of ultra shallow junctions with high carrier concentrations in the source/drain regions. The results of the calculations indicated that the trimer codopants were formed in Si and were stable. The trimer codopants are also able to activate the inactive complexes As₂V and Sb₂V by codoping acceptor atoms that occupy vacant sites. In particular, As₂Al, As₂Ga, Sb₂B and Sb₂Ga resulted in both shallower donor levels and higher solid solubility compared to traditional single donor atoms such as As and Sb.