Theory of metallic contacts on high resistivity solids—I. Shallow traps

Abstract

The theory of injecting contacts on insulating solids containing shallow traps is presented. It is shown that the types of contact an injecting electrode can make on a high resistivity solid can be divided into three convenient categories: (a) separated accumulation regions; (b) overlapping accumulation regions; and (c) low space charge condition. The energy diagrams for metal-insulator-metal systems containing these contacts are discused in detail, and the relationship between the insulator parameters and the work function of the electrodes developed. It is shown that contacts (b) and (c) are the types normally found at a metal-insulator interface, while type (a) normally exists only for very deep lying traps. The low-field conductivity of the insulator for the various types of contacts is calculated. It is shown that overlapping accumulation regions and the low space charge condition cause the insulator conductivity to increase markedly from its intrinsic value; thus the conductivity is extrinsic in nature. Other properties of the contact are also discussed, including the space-charge field at the electrode-insulator interface and the amount of charge injected into the insulator.