Patent GB-697880-A (GB)
Title: Electric circuits including semiconductor devices
IPC: H03D1/10
Filed: 1951-06-26
Abstract: 697,880. Automatic voltage control systems; protective arrangements. WESTERN ELECTRIC CO., Inc. June 26, 1951 [Feb. 16, 1951], No. 15125/51. Class 38 (iv). [Also in Groups XXXVI, XXXIX and XL (c)] An electric circuit comprises a semi-conductor body having a p-n junction and means for applying thereto a reverse voltage greater than the critical voltage of the junction. As the voltage applied in the reverse direction across a p-n junction is increased, the current at first is small and remains approximately constant, but at a critical voltage the current suddenly increases to a large value, thereby providing a constant voltage device. The theoretical aspect of this effect is discussed and information given on factors which affect the value of this critical voltage; values of 150 volts and 800 volts are mentioned, for samples of germanium material. Fig. 1 shows the device used to provide a constant voltage source. The semi-conductor body is produced as a single crystal by slowly withdrawing some of a molten mass of germanium and adding suitable donor or acceptor materials to the melt to change the conductivity type. Subsequent cutting operations are performed to produce the short rod portion 1, 3 containing the p-n junction 5, with larger end portions 2 and 4 which increase the heat dissipating capacity of the device. Low resistance electrodes 10 are applied to end portions 2 and 4 and voltage from source 8 in the reverse direction is applied across electrodes 10. The voltage drop across electrodes 10 is substantially equal to that across the transition layer 5. The voltage from source 8 is slightly greater than the critical voltage of the junction, and with resistance 9, the arrangement provides substantially constant voltage across terminals 10. In this example, gallium was added to the germanium to produce the p-type portion, and the surface of the semi-conductor was treated with antimony oxychloride and the specimen was then dipped in ozokerite wax as a protection against atmospheric changes. To prevent overheating, a cooling blast of air may be applied to the junction, or operation above the critical voltage may be intermittent only. Silicon may be used in place of germanium, and heat treatment at 900 C. for 24 hours may be applied to increase diffusion and increase the critical voltage. Fig. 4 shows an arrangement in which the voltage across terminals 15 is maintained constant in spite of variations in the voltage of source 8, or of the connected load. Devices 16 and 16<SP>1</SP> consist of p-n junction arrangements, arranged to operate in the constant voltage portion of their characteristics. The grid of valve 20 is connected to the junction of resistance 17 and device 16, and the cathode to the junction of resistors 19 and 18, so that variations in the voltage across !eads 15 are amplified by valve 30 and applied through constant voltage device 16<SP>1</SP> to the grid of power valve 25 which operates as a shunt-variable impedance across terminals 15. The arrangement may also bo regarded as a two-stage D.C. amplifier, which also amplifies A.C. signals fed to the grid of valve 20. The p-n junction device may be connected across an output circuit and suitably biased so as to provide a voltage limiter or pulse clipper. It may also be connected across a telephone transmission line and biased below its critical voltage so that it provides protection for equipment against voltage surges due to lightning, induction, or switch operation. Alternatively the device may be connected in series with a bias source so that it is biased at or slightly below the critical voltage, and it may then operate as a non-linear element to serve as a detector for signal modulated carrier waves. The relatively small reactive component of the device used in this way, makes it suitable for use at very high frequencies. Specification 694,021, [Group XXXVI], is referred to.