Patent GB-708899-A (GB)
Title: Improvements in or relating to electric rectifying devices employing semiconductors
Inventor: MATTHEWS KENNETH ALBERT
IPC: H03B7/06
Filed: 1952-10-14
Abstract: 708,899. Semi-conductor trigger and generating circuits. STANDARD TELEPHONES & CABLES, Ltd. Oct. 14, 1952, No. 25722/52. Addition to 686,958. Class 40 (6). [Also in Group XXXVI] A rectifier comprises a semi-conductor body of one conductivity type bearing a low resistance electrode, a region of opposite type conductivity on part of the body surface and a film of the first conductivity on part of the region, an electrode contacting the film, the two electrodes being spaced apart by a distance d = K#T, where T is the lifetime of minority current carriers and K is a constant depending on the electroforming and the turnover voltage required for the rectifier. The device has a high value negative resistance portion in its reverse characteristic, and low turnover voltage so that it may be used for trigger circuits and oscillators. Fig. 1 shows a device similar to that described in the parent Specification, comprising a point electrode 3, and a base electrode 2 connected to coating 4 surrounding an N-type germanium crystal 1. The crystal is etched and electroformed, as described in Specification 681,809, [Group XXXIX], whereby a region of P-type conductivity is formed, and a film of N-type conductivity is provided on the P region due to the injection of donor material during electroforming from the whisker electrode 3. To obtain the improved negative resistance portion in the characteristic, the Specification describes how the spacing between electrodes 3 and 4 may be determined as a function of the lifetime of holes in the semi-conductor body and the electroforming and desired turnover voltage at which the negative resistance portion commences. The point contact may consist of a small plated area, and if the carrier lifetime is sufficiently long, the electrodes may be on opposite sides of a thin slice of semi-conductor. Fig. 10 shows an alternative construction in which the electrode 3 has a spherical end and is placed in a V-shaped groove in the semi-conductor, the base electrode 2 being connected to the coating 4 as in Fig. 1. The voltage-current characteristic of the device has a negative resistance region between two positive resistance regions, and a stable, monostable and bistable circuits and a sine wave oscillator circuit are described. Fig. 11 shows the device arranged as a trigger circuit. The voltage-current characteristic has a negative resistance portion 12, Fig. 13, between two positive resistance portions 31, 14, and to provide a free running circuit, the resistance 19 is selected to have a higher value than the negative resistance and its load line 26 cuts the characteristic at one point 28 only, in the negative resistance portion, which is unstable. Condenser 20 operates to maintain the potential across resistance 19 at the turnover points, so that the cycle 11, 32, 13, 30, 11 is repeated. By arranging that the load line cuts the characteristic at one point only in either of the two positive portions 31 or 14, a circuit having one stable state is provided, and trigger pulses may be applied through terminals 21, to drive the circuit through either of the turnover points 11, 13 to perform one cycle. If resistance 19 has a value less than that of the negative resistance, the load line may be arranged to cut the characteristic at three points, so that a circuit having two stable states is provided. This free running arrangement may be modified to provide sine waves by connecting the primary of a transformer in series with condenser 20.