The relationship between space-charge-limited current and density of states in amorphous silicon

Abstract

Abstract This paper is concerned with the nature of the current-voltage (J-V) characteristics of thin amorphous silicon layers under space-charge-limited conditions. J-V curves have been calculated by using a computer program which employs any arbitrary form of the density-of-states function N(E) as input. The use of simple analytical forms of N(E) illustrates the way in which J(V) depends on the form of N(E) and shows that, under certain conditions, it should be possible to observe the effects of carrier trapping both in deep states near the Fermi level and in tail states remote from the Fermi level. The possibility of observing tail-state trapping at attainable current densities is enhanced by low values of N(E), by working at low temperatures and by using thin samples. Calculations have also been made by using two experimentally determined density-of-states functions, one derived from field-effect conductance and the other from deep-level transient spectroscopy (DLTS) measurements. The corresponding J-V characteristics show wide variations. Comparison with experimental results in the literature shows no evidence for the deep minimum in N(E) derived from DLTS measurements.