S. Yoda

Growth of homogeneous mixed crystals of In0.3Ga0.7As by the traveling liquidus-zone method

We have invented the traveling liquidus-zone method for growing homogeneous mixed crystals. In this method, the solute transport rate is controlled by the temperature gradient at the freezing interface and compositional homogeneity is established easily on the ground, although the actual growth rate is affected by convection in the liquidus zone. Growth rates for producing homogeneous crystals are examined experimentally by changing the temperature gradient in the zone and they are analyzed theoretically. Experimental results agree with numerical analysis qualitatively.

Marangoni flow of molten silicon

Abstract Marangoni flow of molten silicon was studied for a half-zone liquid-bridge configuration. Through flow visualization using an X-ray radiography technique with tracer particles and temperature oscillation measurements, the instability mode for the Marangoni flow was determined. It was found that m=1 and 2 modes appeared depending on the aspect ratio ( Γ= height h/ radius r ) of the liquid bridge. The critical Marangoni number for transition from an oscillatory flow with single frequency to that with multiple frequencies was deduced to be about Ma=1300, based on the calibrated-temperature difference between hot and cold solid/liquid interfaces. A transition was also observed when the oxygen partial pressure of the ambient atmosphere was changed. The flow velocity observed using a tracer particle also showed a dependence on the oxygen partial pressure; the velocity decreased with increasing oxygen partial pressure. By observing surface oscillation using a spatial-phase measurement technique, Marangoni oscillation at the melt surface was successfully distinguished from natural oscillation with eigenfrequencies. Marangoni oscillation ( >1 Hz ) that was not revealed by flow visualization and temperature measurement using thermocouples was also observed. Marangoni flow at a flat surface should be studied, so that the heat and mass transfer process for the Czochralski system can be more clearly understood and controlled.

Video imaging of the melting and solidification processes of the PbBr2PbCl2 system under microgravity

Abstract Using a sounding rocket, real-time observation of the melting and solidification of the PbBr 2 PbCl 2 system sealed in a quartz ampoule was successfully performed under microgravity. The interface shape is convex toward the melt during melting and becomes almost flat on solidification, which agrees well with the results of a computational thermal analysis. The liquid flow observed during melting had a velocity between 0.2 and 1.5 mm/s. This is much higher than expected and is most likely due to Marangoni convection. Although the PbBr 2 melt wets the quartz ampoule, traces of microscopic free-surface areas during solidification are observed on the crystal surface. The microscopic free surface is the origin of Marangoni convection. Results from this “first-time” observation of the Marangoni flow in a liquid sealed in an ampoule, and capable of wetting the ampoule wall, will be useful in future microgravity experiments and will lead to a better understanding of crystal growth from a melt.