GB877422A - Improvements in or relating to semi-conductor devices - Google Patents

Abstract

877,422. Semi-conductor devices. STANDARD TELEPHONES & CABLES Ltd. June 26, 1959 [July 3, 1958], No. 21293/58. Class 37. A point contact germanium device is electroformed by an alternating current of such frequency that the turnover voltage of the junction thus formed does not differ from the value that would have been attained by passage for the same time of an alternating current of higher frequency but of the same R.M.S. value. During electroforming acceptors are subject to diffusion and to drift in the electric field. For thermal acceptors, i.e. acceptor centres produced by lattice disturbances, the drift rate greatly exceeds the diffusion rate, whereas the reverse is true for conventional acceptor impurities. Independent control may be provided over the thermal diffusion and drift by use of a forming current of sufficiently high frequency. In one embodiment a pure alternating forming current is used so that the acceptors diffuse as a result of the heat generated but merely oscillate in the electric field with no resultant drift. If the alternating frequency is sufficiently high the amplitude of this oscillation will be so small that the turnover voltage of the resulting junction will be independent of the point in the cycle at which the forming voltage is cut off. Alternatively a direct-current component of variable magnitude is superimposed on the alternating current to aid or oppose the thermal diffusion in a controlled manner. In a suitable forming circuit, shown schematically in Fig. 4, 25 millisecond pulses of a 1 mc/s. current and direct current respectively are fed together to a point contact diode. Specification 747,198 is referred to in the Provisional Specification.