Patent GB-700236-A (GB)
Title: Electric circuit elements and devices utilizing semiconductive materials
IPC: H01L29/00
Filed: 1949-09-23
Abstract: 700,236. Semi-conductor amplifiers. WESTERN ELECTRIC CO., Inc. Sept. 23, 1949 [Sept. 24, 1948; Sept. 24, 1948], Nos. 24486/49 and 24487/49. Class 40 (4) [Also in Groups XXXVI and XL (c)] An electric circuit element comprises a filament or sheet of semi-conductor material having an ohmic connection at one end, a rectifying connection at a point near to the ohmic connection, and a further connection at a point remote from the ohmic connection. The device may be used for amplifying A.C. or D.C. signals, or storing electric signals. The invention relates to semi-conductor amplifying devices having emitter, collector and base electrodes as described in Specifications 694,021, 700,231, [Group XL (c)], and 700,232. In Fig. 1, a body of semi-conductive material such as high back-voltage N-type germanium comprises a filament or thin slab portion 10 having base and collector ohmic connections provided at enlarged end portions 13 and 14 respectively. The emitter electrode 15 makes rectifying contact with the filament portion. If the emitter is biased with a small positive voltage relative to the base electrode and the collector with a larger negative voltage, signals applied between the emitter and base electrodes result in amplified signals appearing in the collector circuit. Several different modifications are described, Figs 2-8 (not shown), including examples in which the collector electrode also forms a rectifying contact, or in which the rectifying contacts are provided either by point contacts, or by providing ohmic contacts to regions of opposite conductivity type material, or by line contacts. Fig. 10 shows another example utilising an additional bias source 115 which produces a field through the filament body 110. Instead of wide portions such as 11 and 12 of Fig. 1, the semi-conductive material may have regions of increased impurity concentration adjoining the ohmic contact electrodes to provide low resistance contacts to the metal. The emitter-base electrode impedance is low due to the forward bias, and the required high impedance of the collector-base electrode circuit is provided by the high resistance of the length of filament and/or the impedance of the collector rectifying contact which is biassed in the reverse direction. The use of a thin filament enables a strong field to be established giving a high drift velocity to the current carriers from the emitter, so that transit time effects may be reduced to facilitate the amplification of high frequency signals. The use of ohmic contacts instead of point contacts reduces noise and stabilizes the amplification factor. Feedback is governed by the distance between the emitter and the base electrode. If the collector is spaced from the emitter, the transit time may be of the order of microseconds, and the device may be used for delaying or storing a train of pulse signals. For this purpose the field along the filament body 110 should be uniform, and the path of the emitter "hole" current should be rectilinear. Two emitter 116 and collector 119 electrodes may therefore be used as shown in Fig. 19. For each input pulse applied to the emitter 116 the collector current comprises two signals, the first being the "direct" signal which appears substantially instantaneously due to normal potentiometer effect on the total current, and the second being the amplified "delayed" signal due to the arrival at the collector of the hole current from the emitter which has drifted down the filament under the influence of the applied field. The two signals may be distinguished from each other by means of an amplitude-limiter, or by employing a circuitbalancing arrangement such that the direct signal is cancelled out, Fig. 22 (not shown), or by using inductances to isolate the main body portion 110 from the signal, Fig. 23 (not shown). The pulses tend to become distorted to triangular pulses during transit due to dispersion, and if large input pulses are supplied so that the conductivity of the body portion 110 and therefore the field distribution is affected, further distortion effects occur whereby the relative steepness of the trailing edges of the pulses is increased, and frequency selective means responsive to the trailing edges may then be used to detect pulses in the output circuit. The number of distinguishable pulses which may be stored is shown to be #10v where V is the voltage between the emitter and the collector. Figs. 15, 16, 17 and 21 show further alternative arrangements. In Fig. 21, the emitter and collector portions 116A, 119A are of the same conductivity type as the body 110 and rectifying barriers J1, J2 are associated with electrodes 113,114. Figs. 16 and 17 show examples which may be used as delay storage arrangements, or as direct current amplifiers. Phase modulation of signals may be effected by varying the field strength along the filament such as by varying the potential of source 115 in Fig. 10. The process for preparing a thin slab of semi-conducting material is described, including an etching process, and the use of masks for obtaining devices of suitable shape by means of a grit blasting process. P and N-types of material in the examples may be interchanged with corresponding change in bias voltages. Conversion of N to P-type may be effected by electrical heating in the presence of suitable impurity. Specifications 592,260, 592,303, [both in Groups XL], 632,942, and 669,399, [both in Groups XL (c)], are referred to.