In many semiconductor devices the essential principle is the fact that the conductivity of the material is controlled by impurity concentrations, which can be varied within wide limits from one region of a device to another. An example is the p-n junction at the boundary between one region of a semiconductor with p-type impurities and another region containing n-type impurities. One way of fabricating a p-n junction is to deposit some n-type material on the very clean surface of some p-type material. (We an’t just

In the exponent, e is the quantum of charge, k is Boltzmann’s constant, and This absolute temperature.

CAUTION In e,V the base of the exponent also uses the symbol e, standing or the base of the natural logarithms, 2.71828 …. This e is quite different from e = 1.602 x 10-19 C in the exponent. <III Equation (44-23) is valid for both positive and negative values of V; note that V and I always have the same sign. As V becomes very negative, I approaches the value -Is. The magnitude Is (always positive) is called the saturation current.