Hot electrons and negative resistance at 20°K In n-type germanium containing Au − centres

Abstract

Experimental results are presented of the variation with electric field of the capture rate of electrons at Au − centres in n-type germanium at 20°K. The capture rate per centre at low fields is about 2.0 × 10 −12 cm 3 sec −1 and at high fields about 3 × 10 −9 cm 3 sec −1, an increase by a factor of about 1 × 10 3. This is shown to be consistent with the assumption of a transition probability which depends on electron tunnelling through a Coulombic potential barrier, if the energy-loss part of the transition probability decreases with increasing electron energy. Evidence of a shallow trap, other than the compensating donor, is found which supports the interpretation of previous work. It is shown that the current density vs. field curve in the absence of an electrical domain exhibits a pronounced differential negative resistance. The steady state current in the presence of a domain is seen to take up a value above the minimum permissible value, the latter being predicted on the basis of a simple model of domain formation and the principle of least entropy production. The velocity at which the domain migrates towards the positive contact is measured as a function of illumination level and applied field. It is shown to vary in an approximately linear way with illumination level, but its absolute magnitude is lower by a factor of 10 2 than that expected on the basis of a simple model. The situation at high illumination levels is complicated by electron transfer from one gold level to the other and it is not considered in detail.