Patent GB-1412687-A (GB)
Title: Growing crystals from solution
IPC: C30B29/40
Filed: 1973-03-12
Abstract: 1412687 Progressive crystallisation from solution PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES LTD 12 March 1973 [15 March 1972] 11765/73 Heading B1S Mono- or polycrystallline rods are made by progressively crystallizing a liquid solution of a compound dissolved in one of the constituents of the compound, forming in the crystallizable solution by diffusion of at least one of the constituents of the compound more volatile than the solvent a volume of solution containing a concentration gradient and also a layer of constant concentration and maintaining this layer at a constant distance from the crystalline interface by addition of the solvent constituent. The more volatile constituent is preferably supplied to the surface of the solution in vapour form from a container communicating with the surface which is fixed relative to the constant distance. The invention is illustrated with reference to Figs 1(a) and 1(b) wherein the solution is contained in an enclosure 1 which ends in a cone 2 and contains a seed 3. Volatile constituent 5 is contained in container 4 and communicates via 6 with a bell 24 immersed in the liquid constituent. The enclosure 1 may be lowered by means of rod 7 into a furnace 11 which presents successive zones 12, 13, 14, 15 and 16. Gas supplied via 19 maintains the liquid level at 21 via pressure at level 28. The enclosure 1 is lowered at the required growth rate as a function of the height of the column of liquid between surface 21 and interface 20, which interface 20 is maintained at a fixed-level by the regulation of the temperature gradient in zone 16. Vaporization of constituent 5 causes a constant vapour pressure in the space 22 and determines the diffusion of the constituent 5 into the liquid at 17. Solvent utilized in forming the crystal at interface 20, is replaced from the volume of solvent at 23. During formation of the crystal the enclosure 1 is lowered, the bell remains fixed, level 28 falls, pressure in volume 18 increases and the volume thereof decreases as the pressure in 22 remains constant. In this manner the height of liquid column 17 remains constant and a regular crystal 25 is obtained. In another embodiment illustrated with reference to Fig 2 the height of liquid between the crystallization interface 43 and the porous bottom 34 of non- movable tube 32 is maintained constant. In this device the enclosure 31 is movable and slides on tube 32, which latter has a container with grid 38 for the constituent 37 to be evaporated. Volume 44 is of homogenous concentration determined by the vapour pressure of 37 in 46 and 48, and volume 41 has a concentration gradient with diffusion towards the interface 43. Figure 3 illustrates another device operating with the same principle as in Fig 2, and wherein the liquid is contacted with the other constituent outside the device and then circulates through tubes 55 and 52 via surface of perforated plate 65. Rods of semiconductor compounds (III-V) may be obtained. In particular the solvent may be gallium or indium and the volatile constituent may be phosphorus or arsenic.