| Co-Investigator(Kenkyū-buntansha) |
HAYAKAWA Yasuhiro Shizuoka University, Research Institute of Electronics, Associate Professor, 電子工学研究所, 助教授 (00115453)
YAMAGUCHI Tomuo Shizuoka University, Research Institute of Electronics, Professor, 電子工学研究所, 教授 (40010938)
HIRATA Akira Waseda University, Faculty of Science and Technology, Professor, 理工学部, 教授 (00063610)
OZAWA Tetsuo Shizuoka Institute of Science and Technology, Faculty of Science and Technology, Associate Professor, 理工学部, 助教授 (90247578)
OKANO Yasunori Shizuoka University, Faculty of Engineering, Associate Professor, 工学部, 助教授 (90204007)
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| Research Abstract |
We have conducted different types of experiments to obtain information on dissolution and growth of InGaSb ternary semiconductor under microgravity and on earth.
(1) The microgravity experiment performed in the Chinese recoverable satellite and the reference experiment on earth.
(a) the Ga compositional profile of the space-processed sample was uniform in the radial direction, and the interfaces were almost parallel. On the contrary, the larger amount of Ga composition was incorporated in the upper region of the earth-processed sample, and the dissolved zone broadened towards gravitational direction. Numerical simulation results suggested that the GaSb compositional profile in the solution and solution/crystal interface was significantly affected by solutal convection due to compositional difference ; (b) the GaSb with the (111)B plane dissolved into the InSb melt much more than that with the (111)A plane.
(2) Experiments performed using an airplane,
Crystallization studies were done at a
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reduced gravity level of 10^<-2>G using an airplane (flying in a parabolic trajectory) and at normal gravity conditions on earth. During the crystallization of InGaSb under reduced gravity, there were many needle crystals formed. Though different sizes of these needle crystals formed, most of these crystals were relatively large sized. At the same time, most of the needle crystals resulted during the crystallization process done on earth were considerably smaller in size when compared with the crystals resulted in the reduced gravity condition.
(3) Experiments using a drop tower,
(a) During the crystallization of InGaSb, many spherical projections were observed on the surface of the sample. The projections emerged out during the crystallization of InGaSb from its melt due to the reason that the density of InGaSb liquid is larger than that of solid.
(b) The observed projections were found to be similar to the projections observed in the melting and solidification experiment on In/GaSb/Sb done in IML-2. The projections formed under microgravity were almost spherical, whereas, the projection formed under normal gravity was not perfectly spherical. Due to gravitational pull, the top surface of the projection tended to become flat. This showed the influence of gravity on the formation of projections.
(c) The In composition of the crystallized InGaSb varied depending on the existing temperature at the time of formation. This was in accordance with the InSb-GaSb ternary phase diagram.
(4) Uni-directional solidification under a temperature gradient
(a) When the Seed temperature, the heating rate, the holding period, and the cooling rate were fixed at 648 ℃, 20 ℃/min, 40 h, and 0.5 ℃/min, respectively, the length of the crystal portion with uniform In compositional ratio became longer as the temperature was increased from 1.3 ℃/cm to 9.8 ℃/cm.
(b) The crystal length with uniform In compositional ratio became longer with the decrease of cooling rate and the initial In compositions.
(c) The dissolved area decreased with the increase of heating rate.
(d) The shapes of the dissolved region depend on the gravitational direction. They were perpendicular against the gravitational direction for the horizontal furnace, and broadened towards the gravitational direction in the case of the vertical furnace and the inclined furnace.
(5) Numerical simulation on solute transportation as functions of gravity level and g-jitter.
Numerical simulations on the flow and compositional distribution in the solution were performed as the analytical backup for the experimental studies.
(a) Under zero gravity, as there is no flow, dissolved GaSb diffuses from the interface towards a region far from the interface in the solution. This brings about the compositional gradient along the axial direction in the solution, but the Ga composition is uniform along the radial direction. Therefore, the dissolution of GaSb takes place uniformly at the interface. This results in the flat interface. On the contrary, under normal gravity, the Ga composition is not homogeneous in the radial direction. From the stream lines, it can be understood that a high velocity region exists near the solid-liquid interface. This is because a large amount of Ga-rich solution moves to the upper region due to buoyancy as the density of liquid GaSb (6.01 g/cm^3) is smaller than that of liquid InSb (6.32 g/cm^3). This concentrational gradient becomes a driving force of flow at the interface. At the solid-liquid interface, the dissolution of GaSb in the upper region is suppressed as large amount of Ga composition exists in the upper region of the solution. On the other hand, in the lower region of the solution, a large amount of In composition exists. This increases the dissolution of GaSb into the solution to satisfy the binary InSb-GaSb phase diagram. As a result, the shape of solid-liquid interface broadens towards the bottom. These numerical results can qualitatively explain the experimental results.
(b) The flow vector becomes smaller as the gravity level decreases. The shape of the interface becomes parallel with the decrease of gravity levels. With the increase of heating rate in the furnace, the dissolved amount decreases.
(c) The effect of g-jitter on the convection increases as the frequency decreases.
(d) Thermal Marangoni convection enhances the melting near the free surface under both normal and zero gravity conditions. Under the normal gravity field, the contribution of the solutal Marangoni convection to the flow is less than that of the thermal Marangoni convection because of gravitational segregation. Under zero gravity filed, the inteface shape is greatly affected by both the presence of thermal and solutal Marangoni convections. Less
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