Investigation on Mechanism ofFaceted Cellular Array Growth

Yuko INATOMIInstitute of Space and Astronautical Science

Japan Aerospace Exploration Agency

BackgroundSome works on production of high quality semiconductor device

s, for example thin-film silicon single crystals produced by zone melting recrystallization, have reported the break-down from a planar solid-liquid (S/L) interface to a faceted cellular array.

Zone-melting recrystallization of Si on SiO2

Melt growth of In-doped GaAs

Facet shape (natural quartz)

Cellular array structure in metallic solidification

Faceted cellular array structure

Breakdown of S/L interface (naphthalene-1wt.% camphor alloy)

After Fabietti et al.

Objectives

Although many theoretical models have been proposed, there have been few works that experimental evidences are consistent with theoretical mechanisms. The main reason is that it is difficult to quantitatively evaluate the interface kinetics effect, which controls incorporation process of atoms or molecules at the S/L interface, due to buoyancy convection.

Therefore, in order to investigate the phenomena at the interface in facet growth, in-situ observation of concentration and temperature diffusion fields with two wavelength interferometer is carried out using transparent organic material under a microgravity condition.

Crystal growth in microgravity

On Earth In Space

It is difficult to quantitatively evaluate a phenomena at a solid/liquid (S/L) interface during crystal growth on earth due to buoyancy convection.

Temperature and concentration gradients in a liquid become driving forces of the convection and the convection influences a morphological change of the S/L interface.

An application of a microgravity environment in space is considered to be a promising method to investigate the morphological stability of the interface.

Buoyancy convection Crystal growth in convection

Simultaneous measurement for temperature and concentration fields in real time

Relative temperature and concentration fields, T(t) and C(t), can be obtained.

以下の連立方程式を画素ごとに解く。

The refractive index of the alloy melt depends on temperature, concentration and wavelength of the incident light.

1 2

Temperature and concentration profiles (under 1 g)

Interference fringe patterns in liquid obtained by two-wavelength interferometry (under 1 g)

1 = 460 nm

2 = 780 nm

Temperature

Relative concentration

In situ measurement of temperature and concentration fields

(salol - t-butyl alcohol alloy)

POWER Line

Electrical Interface

Laser

Solution Crystallization Observation Facility of ISS（ SCOF)

Mach-Zehender type microscopic interferometer

Precise temperature controller

Image storage and processing unit

Quartz glass cell Specimen

Peltier devices for temperature control of cell

Specimen cell (PFM)

Phase diagram of salol - t-butyl alcohol

Experimental sequence in ISS

[Sample] Salol/t-Butanol (Buthanol conc.: 4, 8mol% (TBD))

[Observation Method] 1. Amplitude Modulation Microscope (AM) 2. 2-Mz Microscope Interferometer (Mz)

Temperature (C)

Melting Point

50~70

25

20~30

T=15C/cm (TBD) R=0 C/min

T=15C/cm (TBD) R=0.05, 0.2, 1.0, 2.0 C/min

Time (min)

Partial Melt Homogenation Facet Growth

Break Down

4

1

3

3

Facet growth of “salol”

Interferometric fringes around the growing crystal

Contribution to society

The obtained results in space can provide fruitful data on creating high-quality materials for industrial use, such as a solar cell and a superconducting magnet.

Crystal growth models for mineral on earth and meteorite in space will be developed based on the result.

Solar cell

Magnetic levitated train Meteorite

Backup charts

Observation results under 1 G(purified salol)

Morphological change of S/L interface (purified salol)

Temperature gradient in the vicinity of S/L interface