Tunneling through thin oxide interface layers in a-Si:H Schottky diodes

Abstract

A detailed study of hydrogenated amorphous silicon (a‐Si:H) surfaces before and after thermal and plasma oxidation treatments was carried out using x‐ray photoelectron spectroscopy. The thickness of the surface oxides is correlated with the electrical properties of corresponding Mo Schottky barrier structures. Oxide layers up to 1.5 nm in thickness cause a decrease of the reverse current of nearly two orders in magnitude, while the forward current is hardly affected. For oxide thicknesses above 2.0 nm a large reduction in the forward current is observed. Surprisingly, the associated tunneling probabilities of the oxide interface layers in the a‐Si:H Schottky diodes are the same as those previously reported for c‐Si‐based tunnel diodes. Tunneling in the a‐Si:H devices cannot be simply described by the properties of a rectangular barrier, which is adopted most frequently in these studies. A potential form where the barrier height increases quadratically with thickness fits the observed tunneling characteristics more quantitatively, both in absolute magnitude and oxide‐thickness dependence of the tunnel current.