Chemical composition and rectifying properties of metal-semiconductor interfaces

The chemical picture of the constitution of semiconductors derived in the previous paper was used as a basis for examining metal-semiconductor interfaces. It was found that the chemical composition of a semiconductor exerts a profound influence upon its ability to form a rectifier. The insulator NiO (of stoichiometric composition) which is green can be converted into a black material with semiconducting properties either by bringing into its lattice excess oxygen ions (heating in an oxidizing atmosphere) or by substituting a monovalent ion for an occasional in a neutral atmosphere. Both treatments lead to crystals with some “missing electrons” or with Ni²⁺ ions taking the place of some Ni³⁺ ions. As a result, they possess electronic conductivity. Oxidation in addition to producing Ni³⁺ ions also produces positive holes which can migrate through the crystal. The replacement of some ions by monovalent ions, however, makes it possible to retain the original structure without producing holes.