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 μm2, 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 film 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.