Submicron contacts for electrical characterization of semiconducting WS2 thin films

We report a new method to characterize the local electronic properties of polycrystalline semiconducting thin films. A lattice of triangular gold electrodes, with a typical area of 0.2 mu m(2), is evaporated on a p-type WS2 film. With the help of a conductive atomic force microscope, the current-voltage characteristics of the contacts established between the gold electrodes and the WS2 him are measured. A linear dependence of the current versus voltage is obtained on gold triangles in contact with grain edges. This indicates a high level of-doping or degeneracy of the semiconductor at the grain edges. The electrodes deposited on flat WS2 crystallites form rectifying diodes with the underlying grains. Barrier heights of 0.56-0.74 eV and diode ideality factors between 1.15 and 2 are determined. Under illumination, open-circuit voltages up to 500 mV can be measured on some contacts. A short response time of the photocurrent is observed (<0.1 ms) when the diodes are reversed biased, which is related to intrinsic properties of the crystallites. When the diodes are forward biased a longer response time is measured (>100 ms), linked to trapping effects at grain boundaries. (C) 1998 American Vacuum Society.