| 摘要 |
In the downward pulling of a crystalline rod through a die from a melt, a convex solidifying surface is maintained by employing a die of thermally anisotropic material, the thermal conductivity of the die in a direction perpendicular to the axis of the rod being at least 10 times that in the direction of the axis of the rod. The thermally anisotropic material may be pyrographite or boron nitride. An n-type thermoelectric rod of an alloy of bismuth selenide and telluride containing iodine may be pulled. The height of the centre of the convex surface above its periphery is not greater than one thirtieth of the diameter of the rod. The temperature gradient in the vicinity of the solid-liquid interface may be in the range of 500-1,000 DEG C./in. The rate of pulling may be 1 in/hr. according to Fig. 1 (not shown), a rod 11 with a convex solidifying surface 50 is pulled through a die 21 from a melt 15 in a quartz vessel 13 #f which has a gas inlet 20 for argon and is heated by a resistance coil 17. Die 21 has an annular recess 51 to assist in the control of the flow of heat, and is supported by an annular metal plate which is cooled by coil 27. In a modification (not shown), the metal plate extends below the die to increase the temperature gradient in the vicinity of the solid-liquid interface. The rod is quenched by passage through oil and a cooling coil 43. According to Fig. 4 (not shown), a rod 11 is pulled from each of four orifices 150 in a die 121 which has outer and inner annular recesses 151a and 151b respectively. |
