Transient space charge limited currents in a-Si:H

Abstract

Transient space charge limited currents in a-Si:H films have been calculated including recent estimates of the density of localized states. The multiple trapping model for an exponential density of states predicts a decay of the current before a transit time proportional to t α−1 × [1 − K t α] −2 where K is a constant depending upon the escape frequency from a trap, the free carrier transit time and α = T/T 0 The space charge limited transit time is (.78) 1/α times less than the space charge free transit time. After a few transit times, the current decays as t α−1 until the final steady state space charge limited current is reached. For a pulse excitation of CV the current is proportional to t α−1 × exp(βt α) where β depends upon α and the free carrier transit time. After a space charge transit time the current decays as t −α and then as t −(α+1).