Investigation of the size-scaling behavior of spatially nonuniform barrier height contacts to semiconductor surfaces using ordered nanometer-scale nickel arrays on silicon electrodes

Nanosphere lithography has been used to prepare a series of ordered, periodic arrays of low barrier height nanometer-scale n-Si/Ni contacts interspersed among high barrier height n-Si/liquid contacts. To form the arrays, ordered bilayers of close-packed polystyrene spheres were deposited onto (100)-oriented n-type single crystal Si surfaces. The spheres formed a physical mask through which Ni was evaporated to produce regularly spaced and regularly sized SUM contacts. By varying the diameter of the latex spheres from 174 to 1530 run, geometrically self-similar Si/Ni structures were produced having triangular Si/Ni regions with edge dimensions of 100-800 nm. The resulting Si surfaces were used as electrodes in contact with a methanolic solution of LiClO(4) and 1,1'-dimethylferrocene(+/0). The current-voltage and photoresponse properties of these mixed barrier height contacts were strongly dependent on the size of the Ni regions, even though the fraction of the Si surface covered by Ni remained constant. Electrodes formed from large-dimension Si/Ni and Si/electrolyte contacts behaved as expected for two area-weighted Schottky diodes operating independently and in parallel, whereas electrodes having nanoscale SUM regions surrounded by Si/liquid contacts behaved in accord with effective barrier height theories that predict a pinch-off 'effect for mixed barrier height systems of sufficiently small physical dimensions.