Yasunori Okano

Experimental and numerical investigations on dissolution and recrystallization processes of GaSb/InSb/GaSb under microgravity and terrestrial conditions

The effects of gravity and crystal orientation on the dissolution of GaSb into InSb melt and the recrystallization of InGaSb were investigated under microgravity condition using a Chinese recoverable satellite and under normal gravity condition on earth. To investigate the effect of gravity on the solid/liquid interface and compositional profiles. a numerical simulation was carried out. The InSb crystal melted at 525 degrees C and then a part of GaSb dissolved into the InSb melt during heating to 706 degrees C and this process led to the formation of InGaSb solution. InGaSb solidified during the cooling process. The experimental and calculation results clearly show that the shape of the solid/liquid interface and compositional profiles in the solution were significantly affected by gravity. Under microgravity, as the Ga compositional profiles were uniform in the radial direction. the interfaces were almost parallel. On the contrary, for normal gravity condition, as large amounts of Ga moved up in the upper region due to buoyancy, the dissolved zone broadened towards gravitational direction. Also. during the cooling process, needle crystals of InGaSb started appearing and the value of x of InxGa1-xSb crystals increased with the decrease of temperature. The GaSb with the (111)B plane dissolved into the InSb melt much more than that of the (111)A plane

The effect of applied magnetic field on flow structures in liquid phase electroepitaxy—a three-dimensional simulation model

Abstract A three-dimensional numerical simulation for the liquid phase electroepitaxial growth of GaAs under a vertical stationary magnetic field was carried out. The effect of magnetic field intensity and non-uniformity on the flow field in the liquid solution was investigated. Numerical results show that the flow patterns exhibit three distinct stability characteristics: a stable flow field up to a magnetic field level of Ha =150, a transitional flow between Ha =150 and 220, and an unstable flow above Ha =220. In the stable region, the applied magnetic field suppresses the flow field, and the flow intensity decreases with increasing magnetic field exhibiting a power law of U max ∝ Ha −5/4 relationship for the maximum velocity ( U max ). In the transitional region, the flow intensity increases dramatically with the increase in magnetic field strength. The flow patterns are significantly different from those in the stable region. The flow field is no longer axisymmetric but still stable. In the unstable region, the flow structure and intensity change with time. Under a strong magnetic field, the flow cells are confined to the vicinity of the vertical wall and exhibit significant non-uniformity near the growth interface. Such strong flow fluctuations and non-uniformities near the growth interface may have an adverse effect on the growth process and lead to an unsatisfactory growth. In this region, the maximum velocity ( U max ) obeys approximately a power law U max ∝ Ha 5/2 . Results show that for a successful growth the effect of applied magnetic field must be optimized.

LiNbO3 single crystal growth by the continuous charging Czochralski method with Li/Nb ratio control

Abstract LiNbO 3 (LN) single crystals with a controlled Li/Nb ratio were grown by the continuous charging Czochralski (CC-CZ) method. After determining crystal growth conditions such as the material charging rate and the thermal fields for melting the charged materials, Li/Nb ratio controlled crystals with a diameter of 20 mm and a length of 40 mm were successfully grown from Li-rich melts (55.0 and 60.0 mol% Li 2 O). The grown crystals were transparent and measurements of the variations in the lattice parameters and the extraordinary refractive index, n e , showed that the Li/Nb ratio was uniform along the growth direction.

Growth of twin-free InP single cystals by the liquid encapsulated vertical Bridgman technique

Abstract We have successfully grown twin-free InP crystals with 50 mm diameter by the liquid encapsulated vertical Bridgman technique. In order to avoid twin formation in the crystals, a flat-bottom crucible was used instead of conventional crucibles with a conical part.

Melt Mixing of the 0.3In/0.7GaSb/0.3Sb Solid Combination by Diffusion under Microgravity

In order to investigate the effects of diffusion and convection on the melt mixing of semiconductors, experiments under microgravity in space and 1-g on earth were conducted. Sandwich combinations of In/GaSb/Sb solids closed in a BN cylinder were heated up to 733° C in space and 744° C on earth, and they were then cooled rapidly. In both samples, many needle crystals were distributed in the whole area. It was observed that the melt mixing in space was controlled by diffusion which was represented with an error function, and the diffusion coefficient of indium was given by a value of 2.4×10-4 cm2/ s. In the earth sample, however, the indium concentration distribution followed an exponential curve. This indicated that both factors, diffusion and thermal convection, have contributed to the mixing of semiconductor melts.

Observation of crystal-melt interface shape in simulated Czochralski method with model fluid

Abstract Czochralski growth of oxide single crystal was modified using crystal and melt of n-icosane (C 20 H 42 ) and convective phenomena in the melt and crystal-melt interface shape were observed. Increasing the crystal rotation rate, crystal-melt interface shape changed from convex to flat and from flat to concave toward the melt. Crystal-melt interface shape was independent of melt depth. In order to clarify the effect of convective phenomena on crystal-melt interface shape, a scaling analysis was carried out and applied to experimental results; it can be suggested that the Marangoni convection is dominant in the melt for this system.

Control of crystal–melt interface shape during growth of lithium niobate single crystal

Abstract The control of crystal—melt interface shape during Czochralski (CZ) growth of lithium niobate (LiNbO 3 , LN) single crystal by crystal rotation was studied experimentally. The critical crystal rotation rate where inversion of crystal—melt interface occured was evaluated from the weight change of grown crystal under various conditions. With application of these and previous experimental results to our previous theoretical results for the crystal—melt interface, it can be said that the Marangoni convection is dominant in the melt and correlation equations based on the Marangoni convection for controlling crystal—melt interface shape are proposed.

Internal radiative heat transfer in Czochralski growth of LiTaO3 single crystal

Abstract In order to investigate the effect of internal radiative heat transfer on growth behavior in the oxide Czochralski single crystal growth process, differently colored LiTaO3 single crystals were grown in N2 + 0.5 vol% O2 and N2 atmospheres. In the N2 + O2 atmosphere, transparent yellow crystals of 55 mm in diameter and 70 mm in length could easily be grown. The crystals have convex interfaces toward the melt. On the other hand, the crystals grown in the N2 atmosphere are brown because of O2 deficiency. The brown crystals have concave interfaces and it was difficult to grow long crystals by using the hot zone with the same structure as that used in the N2 + O2 atmosphere. From measurements of temperature gradient in the growth furnace, temperature changes around crystals in the crucible with O2 introduction into the N2 atmosphere and emitted spectra from growing crystals in the N2 and N2 + O2 atmospheres, it is concluded that increase of the resistance to heat transfer due to the suppression of the internal radiative heat transfer in the colored crystals is responsible for the growth difficulties such as concave interfaces.

Drop experiments on crystallization of InGaSb semiconductor

Abstract Drop experiments have been performed to study the crystallization of InGaSb under different gravity conditions. Formation of spherical projections on the surface of InGaSb during its crystallization was in situ observed using a high-speed CCD camera. Spherical projections showed dependence on gravity during its growth. The projections formed under microgravity were almost spherical, whereas the projection formed under normal gravity was not perfectly spherical. Indium compositions in the spherical projections were found to vary with temperature.

LiNbO3 single crystal growth from Li-rich melts by the continuous charging and double crucible Czochralski methods

LiNbO 3 single crystals with uniformity along the growth direction were grown from 0.5 mol% MgO doped 48.6 mol% Li 2 0 melt and Li-rich melts (51.5, 55.0, 58.0 and 60.0 mol% Li 2 0) by the continuous charging Czochralski method and the double crucible Czochralski method. It was confirmed by measurements of the phase-matching temperature that the Li 2 0 content in seed end and tail end were 50.000 and 50.007 ± 0.003 mol% Li 2 0 in the crystal grown from 58 mol% Li 2 0 melt. Difference of Mg concentration between seed end and tail end in the continuous charging Czochralski grown crystals was within ±0.01 mol% Mg. The melt compositions were kept constant in the crystal growth by the continuous charging Czochralski method. However, a mixing of initial melts between the inner and the outer crucibles occurs before crystal pulling when the crystals are grown by the double crucible Czochralski method from melts with more than 58 mol% Li 2 0 melt.