Tetsuya Arizumi

Computational analysis of the flow in a crucible

Abstract Forced convection of melt in a crucible caused by crystal and/or crucible rotation in a Czochralski crystal growth system is investigated. The dimensionless Navier-Stokes equations governing the fluid motion are computationally solved by the relaxation method. Flow patterns obtained are classified by various combinations of crystal and crucible rotation rates. Radial flow predominates near the crystal with axial flow occurring mainly in the region between the crystal and crucible bottom. If the crystal rotation rate is larger (smaller) than the crucible rotation rate, the fluid near the crystal flows upward (downward). Stagnation surfaces which prevent complete mixing of the liquid are clearly shown in flow patterns. Finally, the circulation time of the fluid is calculated.

Ultrafine powders of TiN and AlN produced by a reactive gas evaporation technique with electron beam heating

Abstract Ultrafine powders of TiN and AlN are produced by evaporating Ti and Al in a low pressure of NH3 or N2 gas by using electron beam heating. Powders produced are studied by means of electron microscopy and X-ray diffraction method. Both powders are confirmed to be pure nitride with cubic crystal structure for TiN and hexagonal for AlN, and to have a particle size less than 10 nm. The formation process of the nitride powder by the present method can be summarized as follows; (1) surface nitridation of the source materials, (2) vaporization of the nitride and (3) condensation into the nitride particles.

Transport Reaction in Closed Tube Process

Transport equations are proposed for vapor growth of materials in closed tube process, considering diffusion and laminar flow as fundamental transport mechanisms. These equations are applied to transport reactions of GaAs and Ge, as well as impurity doping in Ge-Impurity-I2 system. Calculations are compared with the experiment by F. A. Pizzarello for GaAs-I2 system, and with the results of I. B. M. workers for Ge-I2 system. For GaAs-I2 system, the agreement is very good, but somewhat poor for Ge-I2 system.

Thermal Switching in Chalcogenide Glass Semiconductors

The current-voltage characteristics in off state and the switching phenomena are investigated. The results can be well explained by a thermal model based on the self joule heating of the sample. The results are summarized as follows: (1) I-V characteristics in off state can be normalized over a wide range of temperatures and voltages, and the resulting normalized current has an ohmic and an exponential regions. Calculations based on the thermal model agree very well with the experimental I-V characteristics. (2) From the dependences of the switching threshold voltage upon temperature and resistivity, it is found that the switching can be initiated by a thermal process.

The Numerical Analyses of the Solid-Liquid Interface Shapes during the Crystal Growth by the Czochralski Method

The problem of thermal conduction during the crystal growth process is solved computationally using a model simplified to involve the essential features of the Czochralski crystal growth system. In the crystal the Laplace equation is solved, while in the melt the modified Laplace equation taking account of the fluid motion and the Navier-Stokes equations with the bouyant force being considered are solved simultaneously. The solid-liquid interface shapes are calculated as a function of the crystal rotation rate. Without the crystal rotation, the solid-liquid interface shape is concave to the melt and it becomes more concave as the crystal rotation rate increases. This dependence of the solid-liquid interface shape on the crystal rotation rate is explained by taking the fluid motion into account.

Photoconduction of glasses in the TeSeSb system

Abstract The photoconductivity of bulk glasses of the TeSeSb system is measured as a function of light intensity and photon energy. The relative sensitivity ( ΔI / I d ) has linear and square-root dependences on light intensity in low and high illumination intensities, respectively, and is nearly proportional to the square-root of the resistivity at room temperature. The spectral response of photoconductivity, which is calculated by taking into account the effect of surface recombination of carriers, agrees qualitatively with the experimental results. The experimentally determined broad spectral response suggests the presence of band tails below the conduction band and above the valence band. The large residual dark conductivity in the decay response is associated with the presence of many deep trapping centers.

Computational studies on the convection caused by crystal rotation in a crucible

Abstract Detail of the forced convection caused by crystal rotation in a crucible is investigated. The forced flow is characterized by the Reynolds number (Re = a 2 ω s /ν, where a is the crystal radius, ω s is the crystal rotation rate, and ν is the kinematic viscosity) and the crucible size relative to the crystal. For low Reynolds number, the forced convection is formed under the crystal and the remaining region in the crucible is almost quiescent. The fluid in the crucible is partly stirred. For intermediate Reynolds number, the region occupied by forced convection increases axially towards the bottom and radially towards the walls of the crucible. And, for high Reynolds number, forced convection occupies the whole region in the crucible and the vertical flow from the crucible bottom to the crystal occurs. At the same time, an Ekman flow is formed at the crucible bottom and whole of the melt is completely stirred. The effect of the crucible depth on the forced flow is also described. Finally, present results are compared with the Cochrans flow and the validity of the boundary layer theory by Burton, Prim and Slicheter is examined. The radial variation of the boundary layer is explicitly obtained.

Vapor growth of boron monophosphide using open and closed tube processes

Single crystal layers of boron monophosphide as large as 1.0 cm2 × 30 μm were grown epitaxially on silicon substrates from the vapor phase by thermal reduction of BBr3 and PCl3. The layers grown on {111} surfaces were single crystal boron monophosphide of zinc blende structure while the layers on {100} surface were polycrystalline. The undoped single crystal BP layers were always subtype with a resistivity of 5×10−3Ω-cm. Small crystals of BP were also grown by vertical closed tube method. The transport rate of BP was obtained experimentally as a function of iodine concentration.

The Numerical Analyses of the Solid-Liquid Interface Shape during Crystal Growth by the Czochralski Method. Part II. Effects of the Crucible Rotation

Flow pattern of melt and temperature profile are calculated numerically in a crucible in which a crystal is grown by a Czochralski method. The calculation is carried out for cases both the crystal and the crucible are rotated and is compared with the case the crystal only is rotated (Kobayashi and Arizumi: Japan. J. appl. Phys. 9 (1970) 361). The flow pattern behaves differently depending on the relative sense of rotations of the crystal and the crucible. With the same sense of rotation, the flow induced by crystal rotation extends to the bottom of the crucible, and the interface shape becomes more concave towards the melt as the crystal rotation rate increases. The counter rotation makes the flow pattern similar to that caused by crystal rotation alone. The interface shape becomes less concave for low crystal rotation rate and changes to be more concave through most flat with the increase of the crystal rotation.

Electrical Properties of Chalcogenide Glasses of Te-Se-Ge and Te-Se-Sb Systems

The properties of chalocogenide glass semiconductors of Te-Se-Ge and Te-Se-Sb systems are investigated by electrical conduction and differential thermal analysis. When germanium is introduced to a binary Te-Se system, it forms a strong three-dimensional network structure, and increases the glass transition temperature because it is rather easy to form covalent bonds with selenium and tellurium. Introducing antimony into the glass decreases the activation energy remarkably and increases the conductivity, and a further increase of the antimony content promotes the crystallization of the glass; whereas even by increasing the germanium content the crystallization scarcely occurs. The resistivity of the present glasses is expressed by the reiationship, ρ=ρ0exp (ΔE/kT). The pre-exponential factor, mainly determined by the mobility of the carriers, is nearly constant, and independent of the composition.