Mitsuru Ohtsuka

Model for molecular‐beam‐epitaxy growth over nonplanar surfaces

A model for molecular‐beam‐epitaxy growth is proposed to describe the morphology formed on a nonplanar, profiled surface that may consist of multifaceted crystal structures. Anisotropy of growth rate is introduced as a main factor for explaining the observed growth morphology. We show that on the nonplanar surface, the migration of adatoms modifies the growth rate at each point of the growing surface and thus affects the formation of the morphology within the range of migration length. The model can successfully describe the growth behavior including the development of sharp facet edges, since it is formulated in terms of a difference (rather than differential) equation which does not require the continuity of surface slope. The morphology simulated on the basis of this model agrees to experimental results of GaAs growth.

Modeling of molecular‐beam epitaxy and metalorganic vapor‐phase epitaxy on nonplanar surfaces

A model allowing a consistent description of growth evolution on nonplanar surface by molecular‐beam epitaxy and metalorganic vapor‐phase epitaxy is presented. It is shown that the elemental kinetic processes (surface migration, incorporation, and desorption) are reduced to an equation of continuity for an atomic flow on a growing surface. In metalorganic vapor‐phase epitaxy this continuity equation is coupled with the diffusion equation in vapor phase, permitting to calculate self‐consistently the density distribution of reactant species in vapor and of the adatoms in the surface layer. In the model, anisotropic properties of growth are introduced by taking into account the surface diffusion around the atomic steps. The formulation of the model is based on the discrete form of the continuity equation (rather than the differential form) and therefore allows description of the growth behavior including the development of sharp facet edges. The method of simulation for nonplanar growth is illustrated in det...

Syllable-beat-point synchronized rule-based speech synthesis from coded utterance-speed-independent phoneme combination parameters

In a speech synthesizer, each frame for generating a speech waveform has an expansion degree to which the frame is expanded or compressed in accordance with the production speed of synthetic speech. In accordance with the set speech production speed, the time interval between beat synchronization points is determined on the basis of the speed of the speech to be produced, and the time length of each frame present between the beat synchronization points is determined on the basis of the expansion degree of the frame. Parameters for producing a speech waveform in each frame are properly generated by the time length determined for the frame. In the speech synthesizer for outputting a speech signal by coupling phonemes constituted by one or a plurality of frames having phoneme vowel-consonant combination parameters (VcV, cV, or V) of the speech waveform, the number of frames can be held constant regardless of a change in the speech production speed. This prevents degradation in the tone quality or a variation in the processing quantity resulting from a change in the speech production speed.

Simulation of epitaxial growth over patterned substrates

Abstract In order to gain insight into the influence of different parameters on kinetically limited epitaxial growth, we have simulated the growth morphology formed on patterned substrates by molecular beam epitaxy and metalorganic vapor phase epitaxy.

A numerical simulation model for molecular-beam epitaxial (MBE) growth on nonplanar surfaces

This paper presents an improved model for the description of molecular-beam epitaxial growth on nonplanar surfaces. In this model, atomic flows on the growing surface (incident flux, surface migration, incorporation, dissociation, and desorption) are all reduced to a continuity equation that can be solved for the growth velocity. The growth morphology can be simulated using the physical parameters such as the migration length that may depend on the surface orientation. By carrying out the simulations of GaAs growth, we investigated the role of the surface migration in the formation of growth morphology. Results suggest that there exist two types of atomic steps depending on the surface orientation: one is the step acting as a sink for Ga atoms and the other is the step that has almost no capability of capturing Ga atoms.