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 microsc ope, the current-voltage characteristics of the contacts established b etween the gold electrodes and the WS2 him are measured. A linear depe ndence of the current versus voltage is obtained on gold triangles in contact with grain edges. This indicates a high level of-doping or deg eneracy of the semiconductor at the grain edges. The electrodes deposi ted on flat WS2 crystallites form rectifying diodes with the underlyin g grains. Barrier heights of 0.56-0.74 eV and diode ideality factors b etween 1.15 and 2 are determined. Under illumination, open-circuit vol tages 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 rev ersed biased, which is related to intrinsic properties of the crystall ites. When the diodes are forward biased a longer response time is mea sured (>100 ms), linked to trapping effects at grain boundaries. (C) 1 998 American Vacuum Society.