Studies of Localized Charge Injection in Surface Avalanched pn Junctions

Abstract

A new type of gated avalanche diode has been designed to obtain information concerning charge trapping and avalanche injection. This experimental device contains a unique split gate which permits the experimental determination of the centroid of the injected electron flux into the oxide. Because the injected currents are very small and the environment is noisy, special care must be taken to measure the currents accurately. Thus far, experiments with these structures have been confined to heavily doped p-regions forming junctions to lightly doped <100> and <111> oriented n-type silicon. Measurements on these devices show that the centroid of the avalanching region undergoes a transient displacement away from the center toward the p-side of the junction and then returns slowly to the center. Theory has been developed which relates this behavior to the trapping of electrons in the oxide. The new structure can be applied to experiments which reveal the electron trapping properties of the oxide as well as being used to develop understanding of the nature of surface avalanche in the silicon.