Single-crystal – oriented-crystal – and epitaxy growth processes; – Apparatus – For forming a platelet shape or a small diameter – elongate,...
Patent
1996-01-31
1997-11-11
Garrett, Felisa
Single-crystal, oriented-crystal, and epitaxy growth processes;
Apparatus
For forming a platelet shape or a small diameter, elongate,...
117 81, 117 83, C30B 3500
Patent
active
056859074
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and apparatus for preparing single crystals of group II-VI compounds such as ZnSe and CdTe and group III-V compounds such as InP and GaP or of ternary compounds thereof, from which some of their components are easily dissociated and evaporated during crystal growth at high temperatures.
2. Discussion of the Background
As substrates for use in epitaxial growth required to fabricate light-emitting devices such as a light-emitting diode and a semiconductor laser, there have been used single-crystal substrates of group II-VI compounds such as ZnSe, CdTe and ZnS or of group III-V compounds such as InP, GaP and BaAs, depending on the type of the device to be fabricated.
To prepare single crystals of such compounds, various methods have been proposed including liquid-encapsulated Czochralski (LEC) method, horizontal Bridgman (HB) method, vertical gradient freeze (VGF) solidifying method, and vertical Bridgman (VB) method. Of these methods, the VGF and VB methods have been considered to be remarkably promising methods on an industrial scale, since these methods enable the preparation of high-quality single crystals which are comparatively large in size and present less transformation.
In the VGF method, ring-shaped heaters in multiple stages provided in a furnace are so controlled as to form a temperature distribution in the furnace which ranges, with lowering position in the furnace, from a high temperature to a low temperature through the melting point of the compound used. By shifting the melting point zone in the temperature distribution upward from a lower position to a higher position, a source material melt in a crucible placed inside the heaters is gradually solidified from its bottom portion in contact with a seed crystal to obtain a single crystal grown.
The VB method is similar to the above-mentioned VGF method in that heaters in multiple stages are so controlled as to form a vertical temperature distribution. In the VB method, however, a crucible is moved downward to pass through the melting point zone, thereby gradually solidifying the source material melt in the crucible from its bottom portion in contact with a seed crystal to allow a single crystal to grow.
In preparing single crystals of the foregoing compounds by the VGF method or VB method, however, a specific component having a high equilibrium dissociation pressure (hereinafter referred to as a high-dissociation-pressure component) is easily dissociated from the source material melt and evaporated, resulting in a single crystal having a composition varied from an intended one. To alleviate such a variation in composition resulting from the dissociation and evaporation of the high-dissociation-pressure component, Japanese Unexamined Patent Publication HEI 5-70276, for example, has disclosed a method in which a crucible is hermetically sealed in an air-tight vacuum container such as a quartz ampule, thereby growing a single crystal while preventing the high-dissociation-pressure component from being evaporated from the source material melt in the crucible.
With the foregoing method, however, operations of hermetically sealing the crucible in the airtight vacuum container and further opening the sealed container after the growth of the single crystal are extremely intricate. Moreover, if the airtight container is of completely hermetic type, a pressure difference is produced between the inside and outside of the container when the high-dissociation-pressure component is evaporated until the pressure thereof reaches an equilibrium dissociation pressure. Such a pressure difference results in a force acting on the airtight container which may damage the same.
Japanese Unexamined Patent Publication HEI 4-77383 discloses an apparatus in which an airtight container enclosing a crucible is provided in a high-pressure container serving as a furnace to be filled with an inert gas at a high pressure and a pressure buffer passage for pressure equalization is pro
REFERENCES:
patent: 4083748 (1978-04-01), Gault
patent: 4853066 (1989-08-01), Yoshida et al.
patent: 4909998 (1990-03-01), Nishizawa
patent: 5167759 (1992-12-01), Omino
Fujikawa Takao
Kawanaka Takao
Ohmoto Seiichiro
Okada Hiroshi
Sakashita Yoshihiko
Garrett Felisa
Kabushiki Kaisha Kobe Seiko Sho
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