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 show ed an ideality factor one over at least seven decades in current. Iron contamination reduces the minority carrier lifetime and thus increase s the saturation current. The higher the oxygen content in the silicon substrate, the lower the minority carrier lifetime. At a given forwar d current this results in a lower number of excess minority carriers o utside the depletion region and a higher 1/f noise. Czochralski-grown wafers with a high oxygen content have the highest 1/f noise. Epitaxia l and floating-zone wafers did not show 1/f noise above 1 Hz for curre nts smaller than 0.2 mA. Above 0.2 mA 1/f noise was observed because o f series resistance fluctuations, with S-1 proportional to I-2/f. For Czochralski-grown wafers with the lowest values for minority carrier l ifetimes, the noise spectral density was found to be proportional to S -1 proportional to I-k/fA(k-1), with k approximate to 3/2 and A the di ode area. This indicates the absence of perimeter and series resistanc e effects. A model is proposed to explain the current and area depende nce of the noise in diodes. In this model a position dependent 1/f noi se parameter a is assumed. (C) 1997 Elsevier Science Ltd.