Effect of back surface field on photocurrent in a semiconductor junction

Abstract

An analysis has been carried out for a silicon diffused junction having a back surface field, with particular reference to the generation of photocurrent. The minority carrier distribution, and, photocurrent, as a function of width of the base region of this device, has been calculated. It has been observed that for a back surface field silicon diffused junction, the photocurrent reaches its maximum value at a much shorter width of the base layer. The dependence of photocurrent on the base layer impurity concentration has been studied after taking into account the dependence of diffusion length and diffusion constant on the impurity concentration in the base layer. The photocurrent for the same structure having a drift field in the base layer and a low high junction at the back has also been calculated, and the results indicate that the effect of a high-low junction on photocurrent in this case is less pronounced. A qualitative description of the photoeffect in pp + junction has also been included and the importance of including photovoltaic effect at the low-high junction to explain the overall performance of device has been stressed.