Verfahren zur vorbestimmten Verteilung mindestens einer Beimischung im Hauptbestandteil eines festen Körpers aus einem schmelzbaren Ausgangsmaterial

769,674. Treatment of materials by zone melting. WESTERN ELECTRIC CO., Inc. Nov. 14, 1952 [Nov. 16, 1951], No. 17944/55. Divided out of 769,673. Class 82(1) [Also in Groups XI and XXXVI] A method of treating a body of fusible material containing at least two minor ingredients to produce at least two regions in the body in each of which a different minor ingredient predominates comprises forming a molten zone in a part of the body without contacting the molten zone with an electrode, progressively melting the solid at at least one solid-liquid interface to cause the molten zone to expand in volume and then progressively freezing out solid at the said solid-liquid interface to cause the molten zone to contract in at least one direction, the volume of the molten zone being at all times less than the volume of the body. The method is particularly applicable to producing a desired distribution of conductivity-determining impurities in germanium or silicon to form PN and NPN fractions. In one example. an ingot of germanium is treated by the zone melting process of Specification 769,673 so as to have uniform concentrations A and B, of boron and antimony respectively with the antimony predominating so that the conductivity is N type. A block is sawn from the ingot. the surface layer of the block is melted to a depth of X 1 S (Fig. 2) and the layer is then allowed to freeze progressively in an outward direction. Since the distribution coefficient of boron is greater than 1 and that of antimony less than 1, boron predominates in the part X 1 X 2 of the oncemelted layer and antimony predominates in the part X 2 S of the layer thus forming an NPN transition region in the block. The conductivity-determining impurities may be added to the semi-conductor material by means of a pill which is added to or melted with the molten zone or by gas doping to produce the required transition regions. In a further example, a molten zone ee1 (Fig. 4) is formed in a rod of germanium containing uniform concentrations A and B of antimony and gallium respectively, with the antimony predominating so that the conductivity is N type, and the zone length is decreased until the entire zone has refrozen. Since the distribution of gallium is greater than that of antimony, gallium predominates over the parts ed and e1d1 and antimony over the part dd1 thus forming an NPNPN transition region in the rod. An electric furnace (see Group XI) to melt the surfaces of the blocks is also described. Specif