Question

Difference between barrier potential and cut in voltage pn junction

Answer 1

Explanation:

There is a relation between the barrier height at equilibrium which is called the contact difference of potential phi or the built in voltage, or the diffusion voltage of a pn junction diode and its cut in voltage Vci. It is so that Vci increases as phi increases and always Vci is smaller that phi. The built in voltage phi can be expressed by phi= Vt ln (NaNd/ ni^2) with the parameter have their usual meaning. The cut in voltage is the co-sequence of the linear model of the I-V  curve of the diode. It is so that the I-V curve is approximated by two pieces of a straight lines, one is horizontal and the other is inclined the point between them is cosidered as the point of onset conduction and called the cut in voltage. This point is normally reached at a voltage smaller than phi.

When the junction voltage reaches phi a very large current will pass through the diode which is much larger than the current at the cut in voltage. Under normal operating condition of the diode the maximum operating current of the diode is still smaller than that of the current corresponding to current at  the cancellation of the barrier height.

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