Patent GB-694029-A (GB)
Title: Improvements in semiconductive translating devices and in methods of making them
IPC: G01R31/26
Filed: 1949-12-29
Abstract: 694,029. Semi-conductor amplifiers. WESTTERN ELECTRIC CO., Inc. Dec. 29, 1949 [Dec. 29, 1948; Dec. 29, 1948], Nos. 33222/49 and 33223/49. Class 40 (iv). [Also in Groups II, XXXVI and XL (c)] A semi-conductor amplifier having rectifying contacts is treated by applying a voltage between a first rectifying contact and an ohmic connection to the semi-conductor, while a second rectifying contact is also connected to the ohmic .contact, the voltage being of such magnitude that the electrical characteristics of a region in the neighbourhood of the first rectifying contact are permanently altered to improve the amplifying properties. Fig. 2 shows an arrangement suitable for carrying out the treatment. A block of semi-conductive material such as N-type germanium is provided with a low resistance contact to form base electrode 18, and rectifier contacts to form emitter electrode E and collector electrode C. An alternating voltage of about 0.1 volts at 1000 c.p.s. is applied via transformer 41 to the emitter electrode, together with a positive bias voltage adjustable from 0 to 2 or more volts supplied from battery 45. An alternating voltage at 60 c.p.s., and adjustable between 0 and 135 volts is applied to the collector via transformer 48. A direct current source may be included in series with resistance 50. A cathode-ray oscilloscope 62 is connected to display a horizontal deflection proportional to collector voltage and a vertical deflection proportional to collector current. Figs. 4a and 4b shows the voltage-current patterns initially obtained when the emitter is open circuited and closed with a bias of one volt respectively. If the voltage across transformer 48 is increased " over the peak," the pattern changes to that shown in Fig. 4c, the shape changing from position 1 towards position 13 as the emitter bias is increased. At some stage in this process the device will " form " due to a change in conditions in the semi-conductor material below the collector point and when the voltage 48 is reduced again to about 30 volts and an optimum bias between 0 and + 1 volts is applied to the emitter, the pattern will be as Fig. 4d, showing a modulated region corresponding to greatly increased power amplification of the device. The transformed surface region may be symmetrical about the collector or may extend more towards the emitter. If the applied voltages were excessive, or the surface too sensitive, or thei collector and emitter points too close, " over-forming " results as shown in Fig. 4e, in which unstable regions exist. The germanium material may be prepared as described in Specifications 632,942 and 632,980, [both in Group II], and may contain small percentages of antimony. After grinding and polishing, the surface may be etched with a solution containing hydrogen peroxide and hydrofluoric acid, and then washed in water. Drying may be effected by washing in methyl alcohol and acetone. An alternative etchant described includes nitric acid, hydrofluoric acid and copper nitrate. The Specification describes how the power gain of a crystal amplifier may be measured. The rectifying electrodes may consist of phosphor bronze, silver, tungsten, molybdenum, aluminium or platinum. Specification 694,021 also is referred to.