Patent GB-794895-A (GB)
Title: Improvements in or relating to electric semiconductor devices
Inventor: SIM ALAN COUDRAY
IPC: G01R31/26
Filed: 1954-09-01
Abstract: 794,895. Semi-conductor devices. STANDARD TELEPHONES & CABLES, Ltd. Aug. 26, 1955 [Sept. 1, 1954], No. 25424/54. Class 37. A semi-conductor device is formed by applying a pointed electrode to the surface of a semiconductor body and passing a very short (spike) pulse of current through it of sufficient amplitude and duration to produce a molten region over the whole contact area but too short for the establishment of an equilibrium distribution of lattice disturbances. The effect of passing a heavy current into the semi-conductor from a point electrode, which is discussed in Specification 747,198 is to melt the semi-conductor locally or to melt the end of the wire which then dissolves some of the semi-conductor which on recrystallization is of the opposite conductivity type if a suitable electrode material is used. In addition thermal lattice disturbances are produced in the region beyond the molten region. The peak temperature reached at the contact depends on the initial contact resistance which may previously be established by passing a direct or alternating current or a train of pulses of increasing amplitude until stability is achieved. The duration and amplitude of the spike pulse determines the radius r 1  of the molten region. The radius r 2  of the region in which thermal lattice disturbances are produced may be controlled independently by application of a long forming pulse applied before or after the spike pulse. Fig. 4 shows a typical sequence of operations comprising applying a series of stabilizing pulses 9, 1 millisecond apart preceding a spike pulse 10 of 1 Ásec. duration and several amps. in amplitude. The spike pulse is followed by a long forming pulse 11 of 100 mA. and 25 milliseconds long which is cut off exponentially at 12 to prevent too rapid quenching. Equilibrium distribution of thermal lattice disturbances is attained by this pulse. Alternatively a number of spike pulses may be used which will extend the region of thermal disturbance without altering the size of the molten region. To produce a transistor a pointed wire collector electrode of silver arsenic alloy is applied to a body of N type Ge and a 25 millisecond 300 mA. forming pulse is passed through the contact in the forward direction. Spike pulses of increasing amplitude are then applied with intermediate cooling. If too many spike pulses are applied r 1  extends to r 2  and the collector resistance falls to a low value. The resistance may be restored by a long pulse of 500 mA. which increases r 2  without affecting r 1 . When a satisfactory collector for a transistor cannot be made by normal forming using phosphor bronze because of erratic distribution of phosphorus in the wire 1 Ásecond spikes of 5 amps. may be used. Transistors spoilt by an overlong forming pulse may be restored by a large spike pulse. Diodes may be produced from a ground and etched N-type Ge body by application of a 0.75 amp. 1 Ásecond pulse through a wire of aluminium-copper alloy, or from a P-type Si body by application of a 0.5 amp. 1 Ásecond pulse through a Bi plated Ag wire or an Ag wire containing 0.1 per cent As or P.