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| Title: |
Growth of Homogeneous In0.3Ga0.7As
Single Crystals in Microgravity |
| Principal Investigator: |
Kyoichi Kinoshita (Japan Aerospace Exploration
Agency) |
| Co-Investigators: |
Satoshi Adachi |
 |
Japan Aerospace Exploration Agency |
| Yasuyuki Ogata |
Japan Aerospace Exploration Agency |
| Masami Tatsumi |
Sumitomo Electric Industries, Ltd |
| Toru Maekawa |
Toyo University |
| Masayoshi Yamada |
Kyoto Institute of Technology |
| Hirokazu Miyata |
Advanced Engineering Services Co., Ltd. |
| Tetsuya Tsuru |
Advanced Engineering Services Co., Ltd. |
| Yuji Muramatsu |
Advanced Engineering Services Co., Ltd. |
| Takashi Kuroda |
Ishikawajima-Harima Heavy Industries Co., Ltd. |
| Tomoyuki Kuwata |
Ishikawajima-Harima Heavy Industries Co., Ltd. |
| Hideaki Hotta |
Ishikawajima-Harima Heavy Industries Co., Ltd. |
 | Salient
points | Under microgravity conditions, mass transport will not
be disturbed by convection, strain produced by the samples own weight will disappear,
and impurities will not be introduced into crystals because there is no sedimentation.
Therefore, many microgravity experiments have been carried out by many countries
in order to obtain homogeneous, high-quality crystals. Japan has also carried
out several microgravity experiment missions using FMPT (PbSnTe, HgCdTe and InGaAs)
and SFU (GaAs). For fragile materials, such as HgI2 and CdTe, or for
protein crystals, many crystals with lower defect density and better crystallinity
have been obtained. However it is difficult to obtain homogeneous crystals even
in microgravity. Because thermal convection caused by residual gravity disturbs
diffusion mass transport. This unfortunate result is, however, one of the major
initiators of theoretical or numerical research on effects of residual gravity.
This proposal research team has also investigated the effects by numerical simulation.
The team has found that the diffusion dominant condition is difficult to achieve
if the feed crystal was fully melted since the mass transport is easily affected
by convection. The Bridgeman technique is a typical growth technique using a relatively
long melt and has been applied to many microgravity experiments. The research
team has also developed a new growth technique, to TLZ method, as a result of
the numerical simulations. By using the TLZ method, the team has obtained homogeneous
crystals on the Earth. The TLZ method is potentially a superior method for obtaing
homogeneous crystals, but the superiority has only been demonstrated experimentally.
Therefore, the principle of the TLZ method must be verified in the future. In
order to verify the principle, microgravity conditions that can minimize the convection
influence will essentially be required. This experiment will not only contribute
to scientific development in the crystal growth field but also contribute to advancing
the Japanese strategy of information technology.
| Brief
summary of the theme |
| |
Homogeneous Single Crystal Grown by TLZ, Method on the Ground |
The
objective is to verify the principle of the TLZ method that enables growing homogeneous
crystals. A microgravity environment that can minimize convection influence is
essential in order to verify the principle precisely and to understand the TLZ
method correctly, . Verifying the principle will clarify the value of the TLZ
method. In addition, experimental data will contribute to improving crystal growth
techniques on the ground. The target material is In0.3Ga0.7As
in this experiment. This material is used as a substrate material for laser diodes
suitable for optical communication. Unfortunately, however, single crystal growth
is difficult. Before the TLZ method was developed, homogeneous single crystals
of 5 mm in length were the maximum because temperature at an interface must be
fixed for three or more elements but this is quite difficult. Conventionally,
we can control only the temperature distribution but cannot control the concentration
distribution. This means that it is generally difficult to know the interface
location, and thus homogeneity is easily destroyed. The research team has invented
a new growth technique called the TLZ method and can obtain homogeneous single
crystals of 2 mm in diameter and 20 mm in length. This is the longest crystal
in the world (see Fig. 1). The unique feature of the TLZ method is that both the
temperature and the concentration distributions can be controlled. This means
that we can predict the interface location precisely. The TLZ method is a superior
technique for growing homogeneous crystals, but we must understand the principle
of the TLZ method correctly in order to improve crystal growth techniques on the
ground. Microgravity experiments are essential for verifying the principle of
the TLZ method, We have proposed such a microgravity experiment in response to
the International Announcement of Opportunity. In the experiment, we plan to investigate
the recovery process from artificial disturbance by changing the translation rate.
This result will also contribute to optimizing experiment conditions on the ground.
Last Updated : October 1, 2003
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