GB1353917A - Method and apparatus for forming crystalline bodies of a semicon ductor material - Google Patents

Abstract

1353917 Group III-Group V compounds RCA CORPORATION 26 Aug 1971 [4 Dec 1970] 40048/71 Heading C1A [Also in Division B1] A crystalline body of a Group III-V semiconductor compound wherein the Group III element is selected from Al, Ga, In or mixtures thereof, and the Group V element is selected from P, As, Sb or mixtures thereof is prepared by melting a charge comprising the Group III element in elemental or combined form and passing vapours of the Group V element into the molten charge at a point below the surface of the charge so as to react with the available Group III element and form the desired III-V compound and then crystallizing the melt. The melt may be crystallized by gradient freezing, by the Bridgman technique or by crystal pulling in which portions of the reacted melt are slowly crystallized to form a monocrystalline or polycrystalline body. The flow of Group V element vapour into the non-solid portion of the crystallizing melt may be continued during the crystallization. The crystallization may be commenced using a seed crystal on which the material from the melt is epitaxially deposited. The charge used to form the melt may in fact comprise some already formed III-V compound, whereby the desired product is crystallized from a melt comprising a saturated solution of the Group V element in the III-V compound. The monocrystalline or polycrystalline nature of the product varies according to the growth rate used. A suitable apparatus is shown in Fig. 3, where a container 86 under a suitable pressure of inert gas, holds a crucible 90 on a movable rotatable support 88, a susceptor 94, a R.F. heating coil 92 and a heat shield 96. The container 86 also holds a crucible and lid 98, 100, which crucible is raised and lowered by wire 102, and which has a tube 104 passing through its base into crucible 90. The tube 104 may also carry a sealing disc 114 positioned below the liquid sealing material 112 used during the process. In the process the charge 108 comprising Group III element is heated until molten, and then by means of heater 106 the Group V material 110 in crucible 98 is raised to vaporizing temperature and passes down tube 104 which has been immersed in the molten charge 108 so that its tip is adjacent the bottom of the crucible. When the reaction is complete, as is evident from the bubbles of Group V material emerging from the melt, either the tube 104 is raised whilst heater 92 is arranged to impress a suitable crystallizing gradient on the crucible, or the crucible is lowered and crystallization is initiated and continued by the crucible leaving the heating coil. In a further embodiment (not shown) a crystal may be pulled by suitable means from the melt.