A theory of flicker noise in valves and impurity semi-conductors

A theory of contact noise at low frequencies is described It is assumed that this noise is due to diffusion of clusters of mobile impurity centres on to the contact surface, as in Schottky's theory of flicker effect in valves. A cluster disappears in time due to ionization and consequent ionic conduction away from the contact surface. This diffusion-conduction process is used to derive a formula for the flicker noise which is applicable to emission from oxide-coated filaments of valves and to contacts between particles of impurity semi-conductors, as in lead sulphide photo-conductive cells and rectifiers. The spectral power density of the noise is found to depend on current j and frequency f as j x +1 / f x , where 1< x <2. Experimental results for PbS cells, oxide emitters and copper-oxide rectifiers are found to be in good agreement with this law. Carbon resistors are also found to obey this law, and it is suggested that the same mechanism of diffusion of clusters of impurity atoms on to the contact surface between crystals is responsible for the effect.