On the Theory of Noise in P-N Junctions and Related Devices

A discussion of possible sources of noise in p-n junctions is given. The sources are classified into two groups, the first group constituting noise resulting from fluctuations inherent in the electronic system of a p-n junction, the second group constituting noise caused by a fluctuating quantity which exerts a control over the average flow of current. Noise of the first group is investigated, and it is shown to be a result of concentration fluctuations of the minority carrier. The model used for a p-n junction is characterized by a distribution of localized energy states for the minority carrier in addition to the valence and conduction-band states. The local concentration of the minority carrier, p(x, t), fluctuates by body and surface recombination and by diffusion current flow. Fluctuations in p(x, t) constitute an infinite-dimensional random process. A portion of the paper is devoted to reducing the problem to one in a finite number of variables while retaining the physical features of a p-n junction over the frequency range 0¿1/2¿Tp. A noise theory is developed on the basis of the resulting lumped parameter description of a p-n junction. The results of the noise theory are summarized in an equivalent circuit and an appropriate noise generator. Noise characteristics of p-n junction rectifiers and transistors are analyzed. The available noise power of a p-n rectifier is voltage dependent, the equation resembling that of Weisskopf for point-contact rectifiers.