Analysis of double injection transients in amorphous silicon p-i-n diodes

In this article we present results of both experimental and computer modeling studies of transient double injection currents in amorphous silicon p-i-n diodes. After the application of a forward bias step pulse, the current decays until there is a sudden sharp rise, often by two to three orders of magnitude. The delay time for this current increase varies from microseconds to many milliseconds, and it is found to be strongly dependent on the pulse repetition rate, applied bias, degradation state of the sample, and illumination. Our results are in good agreement with computer simulations of these phenomena. The sudden current rise is associated with a change in transport mechanism from electron space-charge limited current flow to bipolar recombination limited current flow. Experimentally and theoretically it is found that in a degraded device the delay time is also very dependent on the spatial position of the metastable defects, with those near the n+ contact having a much more dominant effect than those near the p+ contact.