No abstract

With the discovery of observable tunnel emission through thin insulating films, much attention has been focused on this mechanism of current transfer. The importance of space-charge limited current in somewhat thicker films has also been recognized. We have recently observed a third mechanism of current transfer, namely, the high-fie Id emission of hot electrons from a metal into the conduction band of an insulator in contact with it; this process is identical with Schottky emission into the vacuum. 1 The system consists of a thin insulating layer J between two metals M x and M 2 , a voltage V being maintained between the metals (see Fig. 1). The work function between / and M x is

This paper presents a physical description of the action of ZnO varistors, which are complex ceramic bodies of ZnO grains sintered in an oxide flux; their conductivity is very low at low voltage, but becomes high after a certain breakdown voltage is reached. It is found that depletion layers in the ZnO adjacent to the intergranular layers of oxide flux are the principal barrier to conduction at low voltage. These depletion layers are formed because electron traps in the intergranular layer absorb electrons from the ZnO, and the oxide flux itself is found to be more conductive than the neighboring barriers; conduction within the flux is observed at low temperatures. Electrical breakdown is associated with the completion of trap filling in thin regions of the intergranular layer. This model is supported by a wide range of physical phenomena.

The rate of Auger recombination in materials with a many-valley band structure such as that of PbTe is calculated in this paper. It is found that recombination comes principally from the collision of current carriers in different valleys; the recombination rate can be large at quite low temperatures if the ratio of transverse-to-longitudinal effective masses in a valley is far from unity. The calculated rate sets an upper limit to the resistance of a simple p-n junction in such materials; for material of band gap 0.1. eV, this limit is 6 Ω cm2 at 77 °K.

It is shown that the interaction of magnetostatic waves with a current can be characterized by a coupling constant analogous to, but much greater than, the piezoelectric coupling constant. The theory is applied both to surface and forward-traveling volume magnetostatic waves, and the problems of excitation, reflection, and absorption by a single microstrip and by a narrow-band interdigital transducer are treated. It is found that the coupling constant is close to 0.5 for any reciprocal wave, and is greater for any nonreciprocal wave, when the transducer is in contact with the magnetic medium. These values are too large to allow effective signal processing, since the emitted waves react strongly on the transducer; narrow-band transducers must be lifted above the surface so as to weaken the coupling.