A new derivation of the law of the junctions

In this paper, the author presents students with a new and simple derivation of the law of the junctions. The law of the junctions is crucial to the correct understanding of the operation of the bipolar junction transistor. The integral of the product of the density of energy states and Fermi-Dirac distribution function is used to derive the density of free electrons and holes crossing from one side to another at a pn-junction under an external applied voltage.