GB1060630A - Zone melting processes and apparatus - Google Patents

Abstract

In the formation of a thin rod of semi-conductor material having a substantially constant diameter of less than 5 mm by the relative passage of an inductively heated molten zone 66 (Fig. 1, not shown) through a thicker rod 12 with pulling together with rotation by means 26, the distance d between the solidifying interface 68 of the molten zone and an imaginary plane a through induction coil 62 is maintained constant by control of the rate of stretching. An image of a portion of the surface of the rod about the solidifying interface is projected on to a variable resistance photoelectric cell 72 and variation of the light intensity from a particular range causes passage of a signal to motor 52 for increasing or decreasing the rate of pulling. The image may be of an inside (Fig. 2, not shown) or outside (Fig. 4, not shown) surface portion. Two photoelectric cells in series (Fig. 3, not shown), for both inside and outside portions, may be employed. The use of an image of an outside surface portion about the solidifying interface gives additional control over the diameter of the zone-melted rod.