GB752457A - Improvements relating to p-n junction semi-conductors - Google Patents

Abstract

752,457. Making semi-conductors. GENERAL ELECTRIC CO. Jan. 13, 1954 [Jan. 16, 1953], No. 1024/54. Class 82(1). [Also in Group XXXVI] A PN junction is formed by melting a portion of a monocrystalline body of semi-conductor material of one conductivity type but containing both donor and acceptor materials with different segregation constants, so that at least a part of the melted portion recrystallises with conductivity of the opposite type. In one example, the body consists of a P type germanium bar containing indium as the dominant activator, and arsenic as the minor activator, the segregation constant of arsenic being substantially higher than that of indium. One end of the bar is heated in nitrogen or in a reducing atmosphere to melt a portion, which is then allowed to cool at a slow rate so that recrystallisation starts at the interface between the solid and liquid phases. Owing to the difference in segregation constants, the growing crystal assimilates more arsenic than indium so producing an N type portion 4 on the P type bar 3. Owing to the increasing preponderance of indium in the residual melted portion, the final portion eventually crystallises with excess indium and provides a low resistance portion of P type conductivity. The final tip portion possesses large quantities of both types of activator and may serve as a conductive terminal. In an alternative example, the temperature gradient at the interface is varied during cooling to vary the growth rate. Gallium and antimony are used as the acceptor and donor elements respectively, the segregation constant of gallium remaining substantially constant with increase in growth rate while that of antimony increases. By selecting the proportions of the activators in the initial N type germanium bar, and varying the temperature gradient it is possible to arrange for the first recrystallised portion 10, Fig. 5, to be P type and the later portion 11 to be N type, thus providing an NPN semiconductor body which may be utilised as a transistor. Silicon may be used in place of germanium.