1,147,015. Semi-conductor devices. ITT INDUSTRIES Inc. 18 Jan., 1968 [26 Jan., 1967], No. 2691/68. Heading H1K. A Zener diode is produced by alloying doping material to a wafer through a surface zone produced by the planar process. The alloying step is performed in a temperature gradient in which the temperature increases towards the inside of the wafer. As shown, a P-type region 6 is produced in a wafer of N-type silicon 1 by the planar process using an oxide mask 4. A layer of aluminium is evaporated on to the surface, photomasked, and etched to leave an area 2. The wafer is then mounted on a graphite heating plate in a water cooled quartz reactor containing an inert gas and the aluminium is alloyed through region 6 to produce P + type region 5. The electrode is strengthened by evaporating on a layer of aluminium followed by a layer of silver using the same mask and without breaking the vacuum. The silver layer is tempered and the electrode is thickened by electroless plating. A plurality of such diodes are simultaneously produced in a single wafer which is then subdivided, the individual divider being mounted in a sleeve or envelope with a pressure contact applied to the strengthened electrode. Reference has been directed by the Comptroller to Specifications 1,023,579 and 1,052,673.