Takashi Nakayama - Academia.edu (original) (raw)
Papers by Takashi Nakayama
Physica E: Low-dimensional Systems and Nanostructures, 2003
ABSTRACT The doping properties of Ga2Se3 are investigated by calculating the formation energies a... more ABSTRACT The doping properties of Ga2Se3 are investigated by calculating the formation energies and electronic structures, based on the first-principles pseudopotential total energy method in the local density approximation. It is shown that doped V(IV)-family atoms have the tendency to locate at Se(Ga) sites and P(Si) atom becomes the suitable p(n)-type dopant among various V(IV)-family atoms. One can expect that P doping imports holes into the valence-band top and induces the one-dimensional conductive property for Ga2Se3 semiconductor.
physica status solidi c, 2015
Doping properties in ZnSnAs2 compound semiconductors were studied by the first‐principles spin‐po... more Doping properties in ZnSnAs2 compound semiconductors were studied by the first‐principles spin‐polarized calculation. We have shown that the Ga doping into Zn site produces an ideal n‐type system with small effective mass, not sensitive to the doping concentration, which feature merits the optical isolator application. On the other hand, the Mn doping into Sn site induces a large spin moment around S=1, which merits the spintronics application. When the Mn concentration is increased, however, Mn atoms prefer to locate nearby and the spin moment decreases by the anti‐ferromagnetic interaction between Mn atoms. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
AIP Conference Proceedings, 2007
ABSTRACT Dielectric constants of Si, GaAs, and ZnSe (001) and (111) nano-size films are studied b... more ABSTRACT Dielectric constants of Si, GaAs, and ZnSe (001) and (111) nano-size films are studied by the first-principles calculations. We found that the dielectric constant deviates from the bulk value with decreasing the film thickness and such variation shows characteristic dependences on material kinds, polarization directions, and film orientations.
physica status solidi c, 2013
Oxygen doping into zinc‐family II‐VI semiconductors is studied by the first‐principles calculatio... more Oxygen doping into zinc‐family II‐VI semiconductors is studied by the first‐principles calculation. We found that a large band‐gap reduction occurs for ZnS and ZnSe, while there is little reduction and appears a deep level of oxygen in the band gap for ZnTe. It is shown that such difference reflects the order of energy positions of host cation (Zn) 4s‐orbital and oxygen (O) 3s‐orbital states. We also study the electronic states and stability of oxy‐gen pair. By calculating the formation energy of O pair, we found that O dopants prefer to locate isolated. This is because O atom has so small radius that the pairing pro‐motes a large elastic strain in host system, which feature is in contrast to the case of N pair in III‐V systems.
physica status solidi (b), 2002
ABSTRACT Electronic structures of p-doped Ga2Se3 are calculated by using the first-principles pse... more ABSTRACT Electronic structures of p-doped Ga2Se3 are calculated by using the first-principles pseudopotential total-energy method in the local density approximation. It is found that doped V atoms have the tendency to locate at Se sites and P atom is the suitable p-type dopant among various V atoms. Doping with P imports holes into the top of valence bands and induces the one-dimensional conductive property for Ga2Se3.
physica status solidi (b), 2002
ABSTRACT The relation between the vacancy ordering and optical properties is investigated by calc... more ABSTRACT The relation between the vacancy ordering and optical properties is investigated by calculating the photo-absorption spectra of □1Cd1Ga2Se4 with four kinds of vacancy configurations. It is shown that both the E1 and E2 transitions around 4 to 6 eV show optical anisotropy in the defect-chalcopyrite structure, while only the E2 energy region above 5 eV shows a large anisotropy in the defect-stannite, pseudo-cubic, and its family structures. All these results are closely related to the vacancy ordering in □1Cd1Ga2Se4 compounds.
physica status solidi (b), 2005
GaInS3(CdS)m is the layered natural superlattice system made of the combination of II–VI and III–... more GaInS3(CdS)m is the layered natural superlattice system made of the combination of II–VI and III–VI group semiconductors. Atom order of this system was investigated by using the first‐principles calculation. It was shown that the CdS layers are located inside the GaInS3 layers when their thickness is small, m < 2, while they are located outside the GaInS3 as their thickness increases, large than m = 2. This change of atom order occurs due to the electric field between GaS and InS layers and causes the band‐gap variation as a function of the CdS layer thickness. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Microelectronics Journal, 2009
ABSTRACT Electronic structures of N-layer and N-point defect systems in bulk GaSb were studied by... more ABSTRACT Electronic structures of N-layer and N-point defect systems in bulk GaSb were studied by the first-principles calculations. It is shown that, though the band-gap reduction occurs in both systems, the origins of band-gap reduction are different between two systems, reflecting the difference of topological connection of N atoms.
Journal of the Physical Society of Japan, 1997
ABSTRACT The bonding, electronic structures and dielectric functions of vacancy-ordered orthorhom... more ABSTRACT The bonding, electronic structures and dielectric functions of vacancy-ordered orthorhombic and monoclinic Ga2Se3 are calculated by using the ab initio pseudopotential method and the linear response theory. We have found that in these compounds the bonds around vacancies relax such that the bond length fulfills the order as sp2-like bond >= sp-like bond, and the dangling-bond states of anion atoms located nearest to such vacant sites appear at the valence-band top. These states produce the bonding, i.e. one-dimensional band, along the vacancy-ordering direction and become the origin of large optical anisotropy at the absorption edge. The present results well explain the recent experiments.
Japanese Journal of Applied Physics, 1997
The atomic configuration in layered In2Se3 has been studied from the viewpoint of electronic stru... more The atomic configuration in layered In2Se3 has been studied from the viewpoint of electronic structure. It was found that In2Se3 stabilizes in the layered structure of Se-In-Se=In=Se, where half the In atoms have octahedral bonds (=) and the other half have tetrahedral bonds (-). This structure exhibits semiconducting properties consistent with the results of experiments. Such multicoordination of In atoms occurs due to the large electronegativity difference between In and Se atoms, which also explains why only the In-Se combination shows the layered III2VI3 structure among various III-VI misvalent combinations.
2006 8th International Conference on Solid-State and Integrated Circuit Technology Proceedings, 2006
ABSTRACT Fermi-level pinning of poly-Si and metal-silicide gate materials on Hf-based gate dielec... more ABSTRACT Fermi-level pinning of poly-Si and metal-silicide gate materials on Hf-based gate dielectrics has been systematically studied theoretically. Fermi-level pinning in high- and low-work-function materials is governed by the O vacancy and O interstitial generation, respectively. From our theoretical considerations, the authors have found that the work-function pinning-free-region generally appears due to the difference in the mechanism of Fermi-level pinning of high- and low-work-function materials. Further, the authors also discuss the interface physics between pure metal gates and high-k dielectrics
Surface Science, 2001
Band structure of the 3 p  3 p R30°-Au/Si(1 1 1) surface is calculated by the ab initio pseudopo... more Band structure of the 3 p  3 p R30°-Au/Si(1 1 1) surface is calculated by the ab initio pseudopotential method in a local density approximation. It is shown that the surface is semi-metallic; two bulk-Si valence bands and one Au±Si hybridized conduction band overlap slightly at the center of the Brillouine zone. We found three facts: Au trimers are located higher than the Si topmost layers, the charge redistribution occurs from d to s orbitals around Au due to strong electronic-state hybridization between Au and Si, and the formation of Au±Si bonds induces the charge transfer from Si to Au±Si bonds. All the facts cause the observed increases by Au adsorption of both the work function and the corelevel binding energies of Au and Si.
Japanese Journal of Applied Physics, 1998
The reflectance difference (RD) spectra of nine GaAs(001) surface reconstructions, (2×4)β2, (2×4)... more The reflectance difference (RD) spectra of nine GaAs(001) surface reconstructions, (2×4)β2, (2×4)α, (2×4)γ2, (2×4)β1, (2×4)γ1 and c(4×4) reconstructions on As-rich surface and (4×2)β2, (4×2)α and (4×2)β1 reconstructions on Ga-rich surface, were studied by using the nearest-neighbor s p 3 s * tight-binding method. The surface atomic positions and the tight-binding interaction parameters were obtained by the ab inito pseudopotential calculations. We found that the RD spectra have considerably different features between As- and Ga-rich surface reconstructions. The RD spectra of As-rich surfaces are mainly understood by transitions between top As-dimer states, while the RD spectra of Ga-rich surfaces are explained by the surface electronic states resulting from the sinkage of surface Ga atoms into bulk layers. These calculations are compared with the results of recent experiments.
Japanese Journal of Applied Physics, 1998
Electronic structures and optical properties of layered In2Se3 with various stackings have been s... more Electronic structures and optical properties of layered In2Se3 with various stackings have been studied using ab initio calculation. It is found that since the dangling-bond states of layer-edge Se atoms appear at the top of the valence band, the absorption around the fundamental band gap becomes large for light polarization along the layer direction. This property is common to all stackings and explains well the results of a recent experiment.
Physica E: Low-dimensional Systems and Nanostructures, 2003
ABSTRACT The doping properties of Ga2Se3 are investigated by calculating the formation energies a... more ABSTRACT The doping properties of Ga2Se3 are investigated by calculating the formation energies and electronic structures, based on the first-principles pseudopotential total energy method in the local density approximation. It is shown that doped V(IV)-family atoms have the tendency to locate at Se(Ga) sites and P(Si) atom becomes the suitable p(n)-type dopant among various V(IV)-family atoms. One can expect that P doping imports holes into the valence-band top and induces the one-dimensional conductive property for Ga2Se3 semiconductor.
physica status solidi c, 2015
Doping properties in ZnSnAs2 compound semiconductors were studied by the first‐principles spin‐po... more Doping properties in ZnSnAs2 compound semiconductors were studied by the first‐principles spin‐polarized calculation. We have shown that the Ga doping into Zn site produces an ideal n‐type system with small effective mass, not sensitive to the doping concentration, which feature merits the optical isolator application. On the other hand, the Mn doping into Sn site induces a large spin moment around S=1, which merits the spintronics application. When the Mn concentration is increased, however, Mn atoms prefer to locate nearby and the spin moment decreases by the anti‐ferromagnetic interaction between Mn atoms. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
AIP Conference Proceedings, 2007
ABSTRACT Dielectric constants of Si, GaAs, and ZnSe (001) and (111) nano-size films are studied b... more ABSTRACT Dielectric constants of Si, GaAs, and ZnSe (001) and (111) nano-size films are studied by the first-principles calculations. We found that the dielectric constant deviates from the bulk value with decreasing the film thickness and such variation shows characteristic dependences on material kinds, polarization directions, and film orientations.
physica status solidi c, 2013
Oxygen doping into zinc‐family II‐VI semiconductors is studied by the first‐principles calculatio... more Oxygen doping into zinc‐family II‐VI semiconductors is studied by the first‐principles calculation. We found that a large band‐gap reduction occurs for ZnS and ZnSe, while there is little reduction and appears a deep level of oxygen in the band gap for ZnTe. It is shown that such difference reflects the order of energy positions of host cation (Zn) 4s‐orbital and oxygen (O) 3s‐orbital states. We also study the electronic states and stability of oxy‐gen pair. By calculating the formation energy of O pair, we found that O dopants prefer to locate isolated. This is because O atom has so small radius that the pairing pro‐motes a large elastic strain in host system, which feature is in contrast to the case of N pair in III‐V systems.
physica status solidi (b), 2002
ABSTRACT Electronic structures of p-doped Ga2Se3 are calculated by using the first-principles pse... more ABSTRACT Electronic structures of p-doped Ga2Se3 are calculated by using the first-principles pseudopotential total-energy method in the local density approximation. It is found that doped V atoms have the tendency to locate at Se sites and P atom is the suitable p-type dopant among various V atoms. Doping with P imports holes into the top of valence bands and induces the one-dimensional conductive property for Ga2Se3.
physica status solidi (b), 2002
ABSTRACT The relation between the vacancy ordering and optical properties is investigated by calc... more ABSTRACT The relation between the vacancy ordering and optical properties is investigated by calculating the photo-absorption spectra of □1Cd1Ga2Se4 with four kinds of vacancy configurations. It is shown that both the E1 and E2 transitions around 4 to 6 eV show optical anisotropy in the defect-chalcopyrite structure, while only the E2 energy region above 5 eV shows a large anisotropy in the defect-stannite, pseudo-cubic, and its family structures. All these results are closely related to the vacancy ordering in □1Cd1Ga2Se4 compounds.
physica status solidi (b), 2005
GaInS3(CdS)m is the layered natural superlattice system made of the combination of II–VI and III–... more GaInS3(CdS)m is the layered natural superlattice system made of the combination of II–VI and III–VI group semiconductors. Atom order of this system was investigated by using the first‐principles calculation. It was shown that the CdS layers are located inside the GaInS3 layers when their thickness is small, m < 2, while they are located outside the GaInS3 as their thickness increases, large than m = 2. This change of atom order occurs due to the electric field between GaS and InS layers and causes the band‐gap variation as a function of the CdS layer thickness. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Microelectronics Journal, 2009
ABSTRACT Electronic structures of N-layer and N-point defect systems in bulk GaSb were studied by... more ABSTRACT Electronic structures of N-layer and N-point defect systems in bulk GaSb were studied by the first-principles calculations. It is shown that, though the band-gap reduction occurs in both systems, the origins of band-gap reduction are different between two systems, reflecting the difference of topological connection of N atoms.
Journal of the Physical Society of Japan, 1997
ABSTRACT The bonding, electronic structures and dielectric functions of vacancy-ordered orthorhom... more ABSTRACT The bonding, electronic structures and dielectric functions of vacancy-ordered orthorhombic and monoclinic Ga2Se3 are calculated by using the ab initio pseudopotential method and the linear response theory. We have found that in these compounds the bonds around vacancies relax such that the bond length fulfills the order as sp2-like bond >= sp-like bond, and the dangling-bond states of anion atoms located nearest to such vacant sites appear at the valence-band top. These states produce the bonding, i.e. one-dimensional band, along the vacancy-ordering direction and become the origin of large optical anisotropy at the absorption edge. The present results well explain the recent experiments.
Japanese Journal of Applied Physics, 1997
The atomic configuration in layered In2Se3 has been studied from the viewpoint of electronic stru... more The atomic configuration in layered In2Se3 has been studied from the viewpoint of electronic structure. It was found that In2Se3 stabilizes in the layered structure of Se-In-Se=In=Se, where half the In atoms have octahedral bonds (=) and the other half have tetrahedral bonds (-). This structure exhibits semiconducting properties consistent with the results of experiments. Such multicoordination of In atoms occurs due to the large electronegativity difference between In and Se atoms, which also explains why only the In-Se combination shows the layered III2VI3 structure among various III-VI misvalent combinations.
2006 8th International Conference on Solid-State and Integrated Circuit Technology Proceedings, 2006
ABSTRACT Fermi-level pinning of poly-Si and metal-silicide gate materials on Hf-based gate dielec... more ABSTRACT Fermi-level pinning of poly-Si and metal-silicide gate materials on Hf-based gate dielectrics has been systematically studied theoretically. Fermi-level pinning in high- and low-work-function materials is governed by the O vacancy and O interstitial generation, respectively. From our theoretical considerations, the authors have found that the work-function pinning-free-region generally appears due to the difference in the mechanism of Fermi-level pinning of high- and low-work-function materials. Further, the authors also discuss the interface physics between pure metal gates and high-k dielectrics
Surface Science, 2001
Band structure of the 3 p  3 p R30°-Au/Si(1 1 1) surface is calculated by the ab initio pseudopo... more Band structure of the 3 p  3 p R30°-Au/Si(1 1 1) surface is calculated by the ab initio pseudopotential method in a local density approximation. It is shown that the surface is semi-metallic; two bulk-Si valence bands and one Au±Si hybridized conduction band overlap slightly at the center of the Brillouine zone. We found three facts: Au trimers are located higher than the Si topmost layers, the charge redistribution occurs from d to s orbitals around Au due to strong electronic-state hybridization between Au and Si, and the formation of Au±Si bonds induces the charge transfer from Si to Au±Si bonds. All the facts cause the observed increases by Au adsorption of both the work function and the corelevel binding energies of Au and Si.
Japanese Journal of Applied Physics, 1998
The reflectance difference (RD) spectra of nine GaAs(001) surface reconstructions, (2×4)β2, (2×4)... more The reflectance difference (RD) spectra of nine GaAs(001) surface reconstructions, (2×4)β2, (2×4)α, (2×4)γ2, (2×4)β1, (2×4)γ1 and c(4×4) reconstructions on As-rich surface and (4×2)β2, (4×2)α and (4×2)β1 reconstructions on Ga-rich surface, were studied by using the nearest-neighbor s p 3 s * tight-binding method. The surface atomic positions and the tight-binding interaction parameters were obtained by the ab inito pseudopotential calculations. We found that the RD spectra have considerably different features between As- and Ga-rich surface reconstructions. The RD spectra of As-rich surfaces are mainly understood by transitions between top As-dimer states, while the RD spectra of Ga-rich surfaces are explained by the surface electronic states resulting from the sinkage of surface Ga atoms into bulk layers. These calculations are compared with the results of recent experiments.
Japanese Journal of Applied Physics, 1998
Electronic structures and optical properties of layered In2Se3 with various stackings have been s... more Electronic structures and optical properties of layered In2Se3 with various stackings have been studied using ab initio calculation. It is found that since the dangling-bond states of layer-edge Se atoms appear at the top of the valence band, the absorption around the fundamental band gap becomes large for light polarization along the layer direction. This property is common to all stackings and explains well the results of a recent experiment.