Kazutaka Terashima

Density measurement of molten silicon by an improved Archimedian method

A convenient technique for practicing accurate Archimedian density measurements of molten silicon was developed and the temperature dependence of the density was obtained in the range of about 1440 to 1640°C. The density at 1440°C was about 1% larger than the previously reported value. A change in the dependence slope was observed near 1540°C. Thermal volume expansion coefficients of about 1.0x10-4 and 2.8x10-4°C-1 were obtained for temperatures below and above 1540°C, respectively.

Growth of ZnSe crystals by nonstoichiometric annealing

Abstract The grain growth of polycrystalline ZnSe by nonstoichiometric annealing has been studied. It has been found that grains grew from 10 μm to 10 mm in diameter by annealing in selenium atmosphere for two weeks at 1000°C, while samples annealed under a zinc ambient grew up to 2 mm. The color of the crystals changed markedly; the selenium annealed sample became pure green, whereas those annealed under a zinc ambient remained yellow. The residual impurity concentrations in the annealed samples have been found to be less than those in boules obtained by other techniques.

Magnetic field effect on residual impurity concentrations for LEC GaAs crystal growth

Abstract A horizontal magnetic field applied LEC (MLEC) apparatus, for mass-producing large diameter undoped LEC GaAs, has been newley developed. The detailed magnetic field effect on residual impurity concentrations has been studied. The carbon and boron concentrations have been found to be decreased by the MLEC technique, related to the applied magnetic field strength. Carbon and boron impurity concentrations in MLEC GaAs crystals decreased as the gallium molar ratio in molten GaAs decreased. The carbon concentration in MLEC GaAs decreased by decreasing the argon pressure in a high pressure chamber. The thermochemical mechanism for impurity incorporation into GaAs single crystals has been clarified through this study. The oxidation rate of free gallium and deoxidation rate of carbon oxide are shown to be the rate limiting reactions determining the impurity incorporation rate into GaAs crystals. The obtained results suggest that applying a magnetic field to molten GaAs suppresses the chemical reaction closely related to the impurity incorporation into resultant GaAs single crystals. The experimental results show good agreement with this predicted thermochemical mechanism.

Stoichiometry of undoped LEC GaAs

Abstract Stoichiometry of undoped LEC GaAs has been studied by improved coulometric analysis. The solidus phase boundary shape of GaAs has been predicted, based on experimental results. The congruent point has been found to be on the slightly arsenic-rich side. The solidus boundary shape, extending on the gallium-rich side, has been suggested to be flat, while the other boundary, extending to the arsenic-rich side, has been suggested to be steep. The influence of temperature fluctuations, in the vicinity of the growing crystal-melt interface, on compositional variation along the crystals has been clarified. The magnetic field applied LEC (MLEC) GaAs crystals showed a clear relationship with a predicted solidus phase boundary shape, whereas conventional LEC crystals showed an ambiguous correlation.

Influence of melt preparation on residual impurity concentration in semi-insulating LEC GaAs

Residual impurity concentrations in LEC GaAs crystals have been found to be controllable depending on the time during which the melt is held in the molten state, the water content in the encapsulant and the addition of in-situ melt purification. Carbon, boron and oxygen concentrations varied widely from 1.0x1015, 5.9x1015 and 2.0x1015 to 3.9x1016, 1.5x1017 and 3.3x1016 cm−3, respectively. Through this study, it is suggested that the impurity incorporation and extraction mechanisms are due to reduction-oxidation (redox) reactions at the melt (GaAs)-encapsulant (B2O3) interface.

Characteristics of ZnSe crystals annealed under host atom atmospheres

Abstract The characteristics of ZnSe crystals grown by nonstoichiometric annealing have been studied. Their optical characteristics, the driving force for the anomalous grain growth of polycrystalline ZnSe, and impurity interaction are discussed in terms of optical absorption, X-ray measurements, impurity analyses and TEM measurements. The results of PL measurements suggest that the band gap energy of ZnSe crystals grown under a selenium atmosphere became about 28 meV smaller than that of other crystals grown by other techniques. The dominant driving force for grain growth is the surface energy of polycrystalline ZnSe. A cluster of atoms in a crystal grown under a selenium atmosphere has a tendency to move easily during TEM observation with a focused electron beam. This tendency causes the anomalous grain growth under a selenium atmosphere. The intentionally added impurity, iodine, has been found to suppress the grain growth. The residual impurities were highly concentrated at the grain boundaries.

Precise melt composition control for LEC GaAs

Abstract A precise melt composition control technique for LEC GaAs has been developed by optimizing the direct synthesis process. A linear relation has been obtained between the molar ratios for the initial melt and initial charge ( Ga / As : 1.02−0.92). Temperature and pressure were programmed with an automated system to minimize arsenic loss during synthesis and to maintain high reproducibility.

Low-defect InSb crystal growth by InN doping

Low defect InSb single crystals were found to be grown by doping with InN, using the Czochralski technique. The InN doped InSb crystals were investigated by etching study, and compared with undoped crystals. A drastic decrease was revealed in punching-out defects (P-pits) and saucer-like-pit defects (S-pits), caused by doping with more than 1.5x1017 cm-3. High quality photoconductive infrared detectors were prepared by using the crystal.

Grating axicon for collimating Cerenkov radiation waves.

An axicon optical element that utilizes a diffraction grating has been fabricated for collimating the Cerenkov radiation wave. The grating axicon has the advantage of a simple structure, which can easily be fabricated by the computerized numerical control machining technique. The collimation function of the grating axicon is confirmed for Cerenkov-type second-harmonic generation in LiNbO(3) waveguides, and correction of the aberration caused by substrate anisotropy is investigated. The aberration can be compensated by appropriately inclining either the substrate facet or the grating axicon.

Growth of highly homogeneous InSb single crystals

Abstract A characteristic detect, shaped like the letter “Y”, could be found in the [111] pulled InSb crystal. The carrier concentration in the defect is higher than in other parts, which is detrimental in MOS monolithic IR imaging devices. A high quality InSb single crystal for IR imaging devices was found to be grown by a pulling method using a seed inclined 5–10° from the [111] to the [110] direction. The growth conditions for homogeneous InSb single crystals were discussed.