Patent GB-1366532-A (GB)
Title: Apparatus for the preparation and growth of crystalline material
IPC: C30B27/02
Filed: 1971-04-21
Abstract: 1366532 Crystallizing apparatus NATIONAL RESEARCH DEVELOPMENT CORP 14 April/72 [21 April 1971] 10595/71 Heading B1S Apparatus for the preparation of homogeneous crystalline materials from a volatile crystallisable material comprises an inner growth chamber contained in a main pressure chamber, a liquid seal located between the interior and exterior wall of the inner growth chamber which is sensitive to pressure differences between the interior and exterior of the inner growth chamber and pressure balancing means responsive to the liquid seal for equalising the pressure inside and outside the inner growth chamber. The volatile crystallisable material is preferably prepared in situ and may include dopants. The liquid seal may include a tube containing liquid which may be constructed with a first portion of relatively small cross-sectional area, and a second portion of relatively large cross-sectional area, into which liquid contained in the tube is driven by gas pressure thereby allowing escape of gas. The liquid seal may include a sensor responsive to the position of the liquid in the tube and a control valve responsive to the sensor. The liquid for the seal may be boric oxide and the volatile crystallisable material indium or gallium phosphide, gallium arsenide, zinc selenide, cadmium sulphide, or zincsilicophosiphide. The Fig. 1 shown is a diagram, partly in cross-section of the invention as applied to crystal pulling and includes a main chamber 1 containing an inner growth chamber defined by a pull rod bearing seal block 4 and a cup-shaped envelope 5. The pull rod bearing seal block 4 is fixed to the top plate 2 by growth chamber support bracket 6. The lower end of envelope 5 is held in position by a susceptor 9 which is surround by an RF heating coil 8. The melt 7 is heated by susceptor 9. The pull rod consists of a steel section 11 connected by pull rod coupling 12, to a ceramic lower section 13. A seed and seed holder 14 are attached to pull rod lower section 13. A liquid seal 17 is situated between the pull rod and the well 4b, at the top of the pull rod bearing seal block 4. The seal is kept liquid by heater 18. Seal block 4 is also fitted with pressure balancing bubbler 15, see Fig. 2, consisting of a tube in the block communicating between the inside of the growth chamber and at the other end inverted so that this other end is below the level of liquid seal 17 whereby excess pressure in the inner chamber is relieved by vapour flowing through the bubbler or bubbling through seal 17. In the preparation of a crystal of gallium arsenide gallium is inserted in envelope 5, arsenic in volatile component holder 22, and boric oxide in well 4b. After evacuation of the chambers and filling them with dry inert gas the liquid seal is formed and the gallium and arsenic melted. When the melt has formed a seed crystal is lowered into the gallium arsenide and the crystal withdrawn. Any excess pressure in the growth chamber is automatically balanced by vapour removal through the bubbler. The Specification includes details of pressure balancing sensors and also growth of crystals in a horizontally arranged apparatus.