Image Force in Rectifiers

Abstract

THEORETICAI current-voltage characteristics of copper oxide and selenium rectifiers have been obtained by integrating the so-called diffusion equation¹. The result so obtained involves the distribution of the potential of the current carriers in the semiconductor. In general, this rises to a maximum near the interface between the semi-conductor and the rectifying electrode, and then decreases towards the metal in virtue of the image force e²/4kx² (k is dielectric constant of the semi-conductor), which acts on a current carrier in the semi-conductor when it is close to the metal electrode. With increasing applied reverse potentials this maximum is lowered, thus producing the increase in reverse current density which is familiar from known experimental characteristics. The potential due to the image force is additional to a potential distribution which arises from the physical nature of the barrier region. The case of an insulating barrier², the case of a barrier containing a uniform distribution of spontaneously ionized impurity centres³, and a combination of the two1^4,5 have been treated neglecting the space charge due to the current carriers; the insulating barrier has also been studied⁶ with proper allowance for the space charge due to the current carriers. Only in ref. 2, however, has a theoretical characteristic been given which incorporates the effect of the image force. A general method of taking into account the image force is proposed here, and the results are applied to the copper oxide rectifier.