Investigating the effect of aluminum oxide fixed charge on Schottky barrier height in molybdenum oxide-based selective contacts

Abstract

A tunneling atomic layer deposited (ALD) AlOx layer was inserted in a Si|SiOx|AlOx|MoOx|metal tunnel diode structure to investigate the impact of fixed interface charge on Schottky barrier height. ALD AlOx provides a synthesis-tunable fixed charge and can provide excellent field effect passivation at the SiOx|AlOx interface. A large (>1 × 1012 q.cm−2) negative fixed charge density was expected to decrease Schottky barrier height on p-type silicon and increase Schottky barrier height on n-type silicon by up to 0.4 eV based on an electrostatic model. Fixed charge density and interface trap state density were measured using a thick layer of AlOx in metal oxide semiconductor capacitor structures (MOSCAPs); Schottky barrier height and specific contact resistivity were measured using a tunneling-active layer of AlOx in contacted structures with MoOx. In some samples, HfOx interface layers were inserted between AlOx and silicon to quench the fixed negative charge. The Schottky barrier height was found to vary with processing conditions but did not have a strong correlation with expected fixed charge density. Thus, while fixed charge may play a role in determining the Schottky barrier height, other parameters also have significant affect. Further work is needed to minimize contact resistivity and elucidate other factors impacting the Schottky barrier height.