ABSTRACT
A p–n junction exists in a semiconducting material in the region where the impurity content changes from an acceptor type (p type) to a donor type (n type). These junctions may be formed, for example, by the diffusion of impurity atoms into the surface of a crystal 1 or the segregation of impurities during crystal growth. 2 Single-crystal germanium, the most common material used for such junctions, contains two electronic bands which are involved in conduction processes. These are the valence band which is almost filled with electrons and the almost empty conduction band, which lies about 0.72 electron volt above the valence band. The Fermi energy for the intrinsic material is about in the centre of the gap or forbidden region between these bands. For p material it lies within the gap, but below the centre; for n material, above the centre. 3
