GB606626A - Improvements in translating devices for electric waves and methods of preparing them - Google Patents

Abstract

606,626. Crystal detectors. WESTERN ELECTRIC CO., Inc. Feb. 27, 1946, No. 6129. Convention date, Dec. 14, 1944. [Class 40 (v)] A rectifier element is made by casting an ingot from a quantity of silicon of high purity, to which has been added before fusion a small amount of a metal which produces ions comparable in size to the interstices in the lattice structure of the pure silicon, shaping. an element from the ingot, heat treating the element to produce a thin surface layer of pure silicon, and applying an electrical stress to ionize the added metal and to cause the ions to lodge in the interstices in the surface layer. A suitable metal to add is aluminium, which is added in a proportion determined as described in Specification 602,140. A thin slab 3 cut from the ingot is polished and heated at 1050‹ C. for two hours to produce a layer of vitreous oxide over a thin layer of crystallised pure silicon. The back surface is then polished and nickel-plated and soldered to a brass cylinder 5 inside a cylinder 4 of steel or beryllium copper. A tungsten contact wire 8 having its end ground flat is spot-welded to a nickel pin 6 held in an insulating member 7 made of phenolic resin with a powdered quartz filler. The rectifier 12, 13, Fig. 4, is conditioned by placing it in circuit with a source 15 of alternating current and a load 16 arranged as an harmonic generator. In addition, a D.C. bias from a source 19 may be applied across byepass condenser 17 under control of a key 21. Assuming that the rectifier element 12 is electropositive, the self-bias due to rectification will tend to cause the ions of impurities in the silicon away from the rectifying surface. The large bias from source 19 acts in the opposite direction. As a result, when key 21 is closed, some of the large aluminium ions together with other ions are driven into the surface layer. When key 21 is opened, the ions tend to return to the body of the element, but the larger ions tend to remain in the interstices of the lattice structure of the silicon. Thus, after a number of closures of key 21, the surface layer becomes saturated with aluminium ions which produces a stable element of good rectifying quality.