Osamu Sugino

Efficient n-type doping of diamond using surfactant-mediated epitaxial growth

Fabrication of n-type diamond was studied by performing extensive first-principles total-energy calculations for a number of possible configurations during the epitaxial growth process. We find that spatially correlated codopant N–Al–N, which acts as a shallow donor in diamond, can be effectively formed by using a surfactant-based growth technique. This technique takes advantage of the difference in the growth modes of diamond which depend on surface species: incorporation of carbon into diamond crystal is promoted by surfactants (Al) but is locally prohibited by surface co-dopants (N–Al–N). Thus, the co-dopants are selectively buried in diamond. This approach provides a possible and very effective way to realize dense n-type doping of diamond which has not been possible using conventional techniques.

Covalency, elasticity and electron correlation in Si vacancies

Abstract We present total-energy electronic-structure calculations performed for mono-, di- and multi-vacancies in Si within the local density approximation in the density functional theory. It is shown that each of the covalency, elasticity and electron correlation plays its own role in the atomic structures and the resulting electron states caused by the imperfection in perfect covalent semiconductors.

Effect of strain on band structure and electron transport in InAs

Abstract We have theoretically investigated the band structure of InGaAs and strained InAs on (001) InP by employing the pseudopotentials and the local density approximation. We have extracted band parameters and analyzed electron transport by the Monte Carlo method. 26% higher mobility and 16% higher peak velocity are predicted in strained InAs in comparison with unstrained In 0.53 Ga 0.47 As.

Favorable formation of the C49-TiSi2 phase on Si(001) determined by first-principles calculations

Using first-principles total-energy calculations, we investigated the atomic structure of a very thin Ti film on Si(001) and their intermixing. Our calculations show that the Ti film forms a pseudomorphic body-centered-tetragonal structure on Si(001). We found that intermixing of Ti and Si atoms energetically favors the formation of a C49-TiSi2 phase. We propose a plausible explanation of how the C49-TiSi2 phase and the interfacial structure between C49 phase and Si(001) are formed. We discuss why the transformation of the C49 phase into the C54 phase is inhibited when the TiSi2 dimensions reach the submicron region.

Real-time electron-ion dynamics for photoinduced reactivation of hydrogen-passivated donors in GaAs

Photoassisted reactivation of H-passivated Si donors in GaAs has been demonstrated by first-principles calculations. In order to examine the survival of the excited state, we have applied our recently developed scheme of the ab initio molecular dynamics coupled with the time-dependent Schrodinger equation for electrons. We have found a possible electronic excitation which significantly lowers the dissociation-barrier height from 1.79 to 0.23 eV. This result explains well the recent experiment of carrier recovery by laser illumination [D. Loridant-Bernard, S. Meziere, M. Constant, N. Dupuy, B. Sombret, and J. Chevallier, Appl. Phys. Lett. 73, 644 (1998)].

Fusion of ultra thin carbon nanotubes: tight-binding molecular dynamics simulations

Abstract We investigated the reactivity of ultra thin carbon nanotubes (UTCNTs) with diameter nm , which were synthesized in experiment. Tight-binding molecular dynamics (TBMD) simulations showed that isolated UTCNTs were thermally stable up to about 3000 K . By performing first principles calculations and TBMD simulations, we found that all pairs of UTCNTs coalesced into a single tube, without necessitating the presence of atomic defects.

First principles band structure calculation and electron transport for strained InAs

We have theoretically investigated the band structure of InGaAs and strained InAs on [001] InP by employing the pseudopotentials and the local density approximation. We have extracted band parameters and analyzed electron transport by the Monte Carlo method. 26% higher mobility and 16% higher peak velocity are predicted in strained InAs in comparison with unstrained In/sub 0.53/Ga/sub 0.47/As.

Molecular dynamics study of adatom diffusion on Si(100) surface — importance of the exchange mechanism

Abstract The Si adatom diffusion on a Si(100) surface is studied at temperatures between 1000 and 1300 K through long-time-scale empirical molecular dynamics simulations. Exchange is found to occur with a non-negligible frequency, roughly 1 30 to 1 80 as often as hopping occurs. This has only a minor effect on the diffusion constants parallel to the dimer row, but has a major effect on those perpendicular to the dimer row. In the simulations, a variety of complex exchange events involving up to three surface atoms were observed. The dynamical effects are also discussed by comparing with the static calculations.

First-principles dynamics of defect reactions triggered by electronic excitation

Abstract We investigated the influence of electronic excitation on reactivation of H-passivated impurities in GaAs. By applying the recently developed scheme for the first-principles molecular dynamics coupled with the real-time electron dynamics, the electronic excitation that significantly reduces the dissociation barrier heights of a SiGa–H complex in GaAs was found. This fact indicates strong enhancement of H-dissociation upon the excitation and subsequent reactivation of the Si donors. Moreover, the reactivation mechanisms of the C acceptor are partially reviewed.

Conjugate-Gradient Total-Energy Minimization: Defects in Silicon

We present the first-principles total-energy electronic-structure calculations for point defects in Si within the local density approximation. The highly efficient conjugate-gradient minimization technique is combined with the norm-conserving pseudo-potential momentum-space formalism, and enables us to perform large-scale calculations containing up to 216 atoms in a unit cell. The results provide rich information about the microscopic origins of the structural and electronic properties of defects in Si.