Theory of space charge limited currents

Space-charge-limited currents are important in energy devices such as solar cells and light-emitting diodes, but the available theory from the 1950s finds it necessary to postulate defect states that are distributed in energy in order to match data. Here, we show that this postulate is not warranted. Instead, we demonstrate that dopants and the concomitant Frenkel effect, which have been neglected, control the shape of measured current-voltage characteristics. We also account for the observed peak in the noise power. The new theory can anchor efforts to develop experimental techniques to measure deep-trap levels.