Thermionic Constants of Semi-Conductors

Abstract

IN some recent papers1, we have described a convenient method of determining the thermionic constants of metals. The method consists essentially in determining, at different known temperatures, the rate of effusion of electrons through a small hole in a thin wall of a chamber made of the metal, instead of determining the direct emission from the surface. The advantage of the effusion method over the emission method is this. The expression for emission involves the transmission coefficient of the surface for electrons having the requisite momentum to cross the surface. This coefficient is very sensitive to adsorption of gases at the surface, and may differ considerably from unity. This coefficient, however, is eliminated in the expression for effusion, in the same manner in which the emissivity of the surface for electromagnetic radiations is eliminated when we take the electromagnetic radiations from a cavity through a small hole, instead of directly from the radiating surface. When the transmission coefficient is eliminated, any observed deviation of the A-coefficient in Richardson's equation from its theoretical value may be attributed to a small linear variation of the work function with temperature. Thus one is enabled by this method to determine not only the work function correctly, but also its temperature coefficient.