Impact of silicon substrate, iron contamination and perimeter on saturation current and noise in n+p diodes

In this article two different generations of silicon material from the early-eighties and the mid-nineties are compared. The impact of iron contamination and perimeter on the current voltage characteristics and low-frequency noise of n+p diodes was investigated. All diodes showed an ideality factor one over at least seven decades in current. Iron contamination reduces the minority carrier lifetime and thus increases the saturation current. The higher the oxygen content in the silicon substrate, the lower the minority carrier lifetime. At a given forward current this results in a lower number of excess minority carriers outside the depletion region and a higher I/fnoise. Czochralski-grown wafers with a high oxygen content have the highest l/fnoise. Epitaxial and floating-zone wafers did not show I/fnoise above I Hz for currents smaller than 0.2 mA. Above 0.2 mA l/f noise was observed because of series resistance fluctuations, with SI oc P/f.F or Czochralski-grown wafers with the lowest values for minority carrier lifetimes, the noise spectral density was found to be proportional to SI cc Zk/fAX-‘, with k z 3/2 and A the diode area. This indicates the absence of perimeter and series resistance effects. A model is proposed to explain the current and area dependence of the noise in diodes. In this model a position dependent I/’ noise parameter a is assumed