Electrical Characteristics of the Junction in a Simplified Selenium Rectifier Cell

The selenium-cadmium contact is a simplified version of the commercial selenium rectifier and is studied with the purpose of understanding the physics of contact resistance asymmetry. A theory by W. Schottky, which predicts the contact resistance at zero voltage and the course of this resistance with d-c reverse bias, is not adequate to account for the experimental data. An attempt is made to extend the theory by assuming a fraction of the bromine ions in the selenium to be free. Agreement with experiment is obtained for low voltages at a high temperature, but for high voltages at all the temperatures employed there is marked disagreement. The theory developed is sufficiently general to conclude that the contacts studied have either a polarizable layer less than 10^-5 centimeter thick between the cadmium and selenium, or there is a mechanism of deactivation of bromine ions at higher voltages. The experiments do not distinguish between the alternatives.