The Dependence of Capture Rate on Electric Field and the Possibility of Negative Resistance in Semiconductors

It is pointed out that the rate of capture of electrons and holes by charged centres should depend markedly on electric field strength when this is high enough to produce hot electrons. In particular the capture rate for an attractive centre should decrease while the rate for a repulsive centre should increase as the field rises. Each effect will alter the steady state density of carriers. For the case of repulsive centres a decrease in carrier density will occur and the possibility of using this phenomenon to produce a negative resistance state in the semiconductor is discussed. Suitably compensated n-type germanium crystals containing copper, nickel or gold appear to have the requisite properties for exhibiting negative resistance at temperatures low enough for the thermal ionization rate of the centre to be small. It is pointed out that the long time constants involved in the process preclude the use of short pulse fields.