Patent GB-905398-A (GB)
Title: Improvements in or relating to semi-conductor devices
IPC: H01L29/00
Filed: 1959-02-13
Abstract: 905,398. Semi-conductor devices. PHILIPS ELECTRICAL INDUSTRIES Ltd. Feb. 13, 1959 [Feb. 15, 1958], No. 5076/59. Class 37. A circuit arrangement comprises a semiconductor body having two electrodes of opposite conductivity types separated by a highohmic part and a control electrode which is situated so that its associated variable depletion layer may interrupt the current path between the other two electrodes without involving punch-through effect. Fig. 1 shows an intrinsic germanium wafer with an N-type control electrode 2, a P-type surge electrode 4, and an N- type annular base electrode 6. The surge and base electrodes form a PIN diode structure, the current path of which may be penetrated by the depletion layer produced by reverse biasing of control electrode 2. If the surge electrode 4 is floating, its potential is equal to that of the control electrode 2 minus the pinch-off voltage, which may be small. Current between the base and surge electrodes can occur during pinch-off conditions due to the injection of carriers into the depletion layer from the surge electrode which react, or combine with carriers from the base electrode. Thus a diode rectifier with controllable threshold voltage can be provided, the threshold control voltage being fed to electrode 2 while the signal to be rectified is fed to surge electrode 4. In an alternative arrangement, the surge electrode 4 is annular and encloses a central base electrode 6 which is surrounded by a groove 30 to prevent the depletion layer reaching electrode 4, causing punch-through effect between the control and base electrodes which would result in a large base-control current. In a further arrangement, Fig. 7, the surge and base electrodes are both situated beneath the control electrode, but the base electrode is provided with a further low-ohmic layer of material of opposite conductivity type to that of the control and base electrodes, which prevent the depletion layer from reaching the base electrode. This inner low ohmic layer may be provided by adding a rapidly diffusing impurity to that used for forming the alloyed base electrode. The control electrode may be provided by an alloying process utilizing bismuth and arsenic, the base by using indium and gallium and the surge electrode by using indium and arsenic. The semi-conductor may consist of germanium, silicon, gallium arsenide or indium phosphide. Point contacts may be used in place of alloyed junctions provided they have a similar injection characteristic, e.g. a tungsten whisker could replace a P-type alloyed electrode. High ohmic N or P- type or compensated material may be used in place of intrinsic. The device may be used to provide a negative resistance by connecting a load between the control and base electrodes. Although the surge electrode potential follows that of the control electrode the control current is linearly proportional to the surge electrode current, the ratio being equal approximately to the ratio of carrier mobilities, i.e. about 2 for germanium. Consequently the connection between surge and base electrodes present a negative differential resistance. A saw-tooth relaxation oscillator (Fig. 10a, not shown) may be provided by connecting a capacitor 42 between surge and base electrodes, which when a negative voltage is applied to the base electrode charges through resistor 41 until the surge electrode conducts to discharge the capacitor through the control electrode 2 and resistor 40. The device may be used as a switch or trigger circuit, or to provide delayed A.V.C.