GB820611A - Improvements in or relating to semi-conductor diodes - Google Patents

Abstract

820,611. Semi-conductor diodes. MULLARD RADIO VALVE CO. Ltd. Aug. 12, 1955 [Oct. 18, 1954], No. 29916/54. Drawings to Specification. Class 37. A semi-conductor diode comprises a semiconductor single crystal which is thicker than the diffusion length of minority carriers and in which the lifetime of minority carriers is less than 5 Á seconds. A crystal in which the lifetime is less than 5 Á seconds may be made from a bar of Sb doped N-type Ge of 0.4-2 ohm cm. resistivity, obtained by zone levelling, by .electrolytically coating it with Ni circa 0.1- 100 Á thick, heating at 700-800‹ C. for 2-5 hours in an inert atmosphere such as nitrogen, and cooling over a period of 10 minutes to an hour to room temperature. The bar is then cut into slices 30 thou. thick and an alloy junction electrode is formed by fusing a blob of In to one face of the slice, an ohmic nickel solder electrode being provided on the other face. The desired lifetime may also be obtained by using Cu or Fe instead of Ni, Cu also acting as an acceptor impurity. The lifetime may alternatively or additionally be obtained by a surface treatment such as sand blasting or etching in a fluid containing ions such as Cu which increase recombination rate at the surface, by bombardment with electrons and neutrons, or by heating to a high temperature and cooling quickly. As a further alternative suitable material is obtained by placing measured amounts of impurity materials determining conductivity and lifetime respectively, e.g. Sb-Ge alloy and Cu on a bar of Ge in contact with a seed crystal and obtaining a. uniform crystal therefrom by zone levelling. Alternatively a single impurity which controls both conductivity and minority carrier lifetime may be used in this process.