A pn junction is formed from two different semiconducting materials in the form of identical cylinders with radius 0.165 mm. In one application electrons per second flow across the junction from n to the p side while holes per second flow from p to the n side. (a hole acts like a particle with charge .) We have to find (a) the total current and (b) the current density.

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(a)

Electrons carry negative charge. Therefore, when they flow from the n to the p side of pn junction they contribute to electric current as flow of positive charge from p to the n side of the junction. And, holes carry positive charge equal in magnitude to the charge of electrons and their flow from p to the n side of the junctions adds to the current flow of electrons from n to the p side.

It is given that electrons per second flow across the junction from n to the p side and holes per second flow from p to the n side. Thus the total current flow through the junction is

(b)

Radius, r, of the junction is

Therefore, the current density at the pn junction is