Tsuyoshi Aisaka

Low and anisotropic barrier energy for adatom migration on a GaAs (110) surface studied by first-principles calculations

We determined potential-energy surfaces for Ga and As adatoms on a GaAs (110) surface by first-principles calculations in order to understand the epitaxial growth mechanism. We found small migration barrier energies for Ga and As, which explain the long atom-migration length suggested by experiments. We also found that Ga migration is one dimensional and As migration is two dimensional, and that, for both Ga and As adatoms, the sites near As of the topmost layer are stable while those near Ga are unstable.

First-Principles Calculation of the Epitaxial Growth of GaN(0001)

The epitaxial growth of GaN(0001) is studied microscopically using the first-principles calculation. Because of the unusual nitrogen kinetics on the truncated GaN(0001), we found that the most stable site for nitrogen adatoms is not the original wurtzite lattice site but the H3 site for the case in which there is one N adatom and also the case in which there is one N adatom and one Ga adatom on the (2×2)-Ga surface. In order to locate the N adatom at the original wurtzite site naturally, two Ga adatoms are needed for each N adatom on the (2×2)-Ga surface.

Arsenic adatom migration on a GaAs(100) surface using a first-principles calculation

The hopping barrier energy of the As adatom on the Ga-terminated GaAs(100) surface has been studied by using a first-principles calculation. It has been assumed that there are As adatoms on the Ga-terminated surface and each single As adatom is moved on it during epitaxial growth. The simple straight-line paths were applied to estimate the hopping barrier energy. It is found that the hopping barrier energy of the As adatom on the Ga-terminated GaAs(100) surface is anisotropic and that the hopping barrier energy of the As adatom is lower than that of the Ga adatom. The calculated results agree with the results from the Monte Carlo simulation.

Theoretical analysis of angle-resolved photoemission for simple metals

Abstract A theoretical analysis of the angle-resolved photoemission spectrum is presented by using a dynamical multiple scattering formalism for photoelectrons. Because of the multiple scattering effect of photoelectrons and the mean free path effect for both the initial and final states of photoexcited electrons, the calculated spectrum leads to a different peak position compared with that of the band calculation using the same muffin-tin potential. The discrepancy between our calculation and recent experiments is very small for Al(100) and still large for Na(110). Surface effects have been also discussed.

Theoretical investigation of migration of group V adatoms on GaAs(001) surface

The microscopic migration of group V adatoms on a Ga-terminated GaAs(001) surface is investigated by performing first-principle calculations using density functional theory and a slab model of the surface. It is found that the hopping barrier energies of the As and P adatoms on Ga-terminated GaAs(001) surface are anisotropic and that the hopping barrier energies of those are lower than that of the Ga adatom. Comparing the hopping barrier energies of the As and P adatoms, the migration of the As adatom is easier than that of the P adatom.

Dynamical calculation of an ARUPS spectrum for a Si(100)(2 × 1) surface

Abstract A dynamical calculation of an angle-resolved ultraviolet photoemission spectrum from a Si(100)(2 × 1) reconstructed surface is presented. The layer-KKR calculation scheme is used with an empty sphere at every interstitial site to make the silicon crystal a close-packed structure. The calculation shows an extra peak which was considered as evidence of a c(4 × 2) structure. The source of this extra peak would be the photoexcitation transition from one initial surface state with dispersion to a complicated final band structure.

Role of the interatomic interaction in electronic structures. II. Valence-band photoemission

For pt.I see ibid., vol.14, p.2525 (1984). The importance of interatomic interactions in the problem of electron correlation for photoemission is proposed through examinations in the T-matrix approximation. It is found that, for the band narrowing due to the correlation effect, the contribution from the interatomic interaction is comparable with that from the intra-atomic one, while the satellite binding energy is essentially determined only by the strength of the intra-atomic interaction. From the above result it is concluded that the interatomic interaction improves the consistency of the band narrowing and satellite binding energy, which the T-matrix approximation calculation in the Hubbard model cannot. It is also suggested from the calculation for the intensity curve of valence-band XPS that the interatomic interaction may be the main origin of the observed asymmetric distortion of the main curve.

Quantum-Mechanical Calculation for Drude's Absorption in Simple Metals

The intrabant absorption of light for aluminium, sodium and potassium is calculated quantum-mechanically, starting from the current correlation formula. The results obtained are compared with both experimental data and the Drudes formula. With regard to the electron-phonon coupling constant, the one found by the pseudo-potential method is used for aluminium and the Bardeens formula for sodium and potassium. The contribution from the Umklapp processes is estimated as exactly as possible, extending the Zimans treatment to the present case. The results obtained for aluminium and sodium are in good agreement with experimental data. The frequency dependence given by the theory agrees well with that by the Drudes theory for the three metals. It is found that the contribution from the Umklapp processes is very large compared to that from the normal processes.

Migration Process on Ga-Terminated GaAs(001) Surface during Molecular Beam Epitaxial Growth

(ReceivedOctober 11, 1999) The hopping barrier energies of As adatoms on smooth GaAs(001) surfaces have been investigated using the first-principle pseudopotential density functional approach. The hopping barrier energies were calculatedfor a few surface structures. We foundthat the migration of As adatom exhibits anisotropy as well as that of Ga adatom and the hopping barrier energy for As adatom is smaller than that for Ga adatom. These results agree with the results of recent Monte Carlo simulations.

Role of the interatomic interaction in electronic structures. I. Band distortion

The effect of the interatomic interaction on the band distortion in a ferromagnetic state is investigated within the Hartree-Fock approximation, with particular attention given to nickel. New ordering parameters for the band disortion caused by the interatomic interactions are introduced. It is found that spin-up and spin-down bands are distorted in a different manner, while the intra-atomic interaction does not cause this band distortion even in the many-band case. For exchange interactions of short range it is shown that the present treatment is equivalent to the band calculation. The ordering equations in the one-band model are solved numerically, with the result that spin polarisation is always accompanied by band distortion.