Methods of avoiding edge effects on semiconductor diodes

The importance of diode edge effects in practical semiconductor devices and in test structures for electrophysical investigations including power devices, devices utilising avalanche effects, and radiation detectors is discussed. The main effects are on reverse characteristics introducing premature breakdown or excess currents. Experiments clarifying the role of field distribution and surface treatment of the edge and the application of simple methods of improvement, such as using overlay electrodes or surface protection are discussed. A description is given of guard-rings (single, double and multiple), formed by diffusion or other means, used to improve the characteristics of both Schottky and pn diodes. Emphasis is placed on summing-up various physical principles used rather than giving details of fabrication. The main discussion is on silicon devices but examples are also taken from compound semiconductors. (author)