Impact of the Frequency Dependence of the Parasitic Admittance on the Diffusion Noise of a Diode Junction at Low Bias

In this article, we report for the first time that the well-established diffusion noise can be apparently increased in large proportions and that such a situation can be very common at some specific frequencies in the p-n junction structures operating at a very low direct bias current. Noise theories and the associated measurement techniques are a major issue for the emerging semiconductor technologies, the development of accurate computer-aided design (CAD) models, and the designing of low-noise circuits and systems. The conventional shot noise model usually satisfactorily describes the p-n junction noise in solid-state devices, such as diodes and transistors. It has proven to be very efficient for many different conventional and advanced semiconductor technologies. However, alterations may sometimes be needed as previous works indicate scenarios where this so-called shot noise exhibits deviations from the theory, which translates into some noise suppression. In this article, we report on alterations that look like low-frequency diffusion noise enhancement (unexpected noise increase). It occurs at low current levels, for many generic commercially available diodes and the p-n junctions in transistors. Therefore, we propose an appropriate electrical noise model that satisfies both the low-frequency noise experimental data and the electrical behavior of the devices observed from impedance spectroscopy. We also evaluate this model as the ambient temperature is varied. Finally, it is discussed how this model can be connected to the conventional van der Ziel shot noise model and a better insight on the possible origin of such diffusion noise enhancement is provided.