Equivalent circuit analysis of noise in bulk semiconductor devices

Equivalent transmission-line analogs may be developed to advantage for the analysis of noise in bulk semiconductor devices. We discuss first a transmission-line analog for the law of conduction and diffusion of a single species of charge carriers that experience small disturbances from equilibrium. Through the use of Nyquist´s theorem it is possible to obtain the power spectra of the noise sources of the equivalent transmission-line circuit at thermal equilibrium. Next, an equivalent circuit can be obtained if there is more than one charge carrier. This circuit is generalized to the case of drifted carriers and applied to the metal-semiconductor-metal (MSM) diode and to the small-signal analysis of the Gunn effect. We show how the equivalent circuit for the Gunn effect gives, by inspection, a lower bound on the noise measure achievable with a Gunn diode. We find that the Gunn diode has noise measures exceeding the lower bound. A traveling-wave Gunn device achieves the lower limit.