The strain applied to transition metal dichalcogenides (TMDs) reduces their energy bandgap, and local strains result in a funnel-like band structure in which funneled excitons move toward the most strained region. Herein, a funnel device based on asymmetrically strained WS2 and MoS2 is reported. Asymmetric strains are induced by transferring the TMD flakes onto a fork-shaped SU-8 microstructure. Raman and photoluminescence spectra peaks are shifted according to the morphology of the SU-8 microstructure, indicating the application of asymmetric strains to the TMDs. To investigate whether funneled excitons can be converted to electrical currents, various devices are constructed by depositing symmetric and asymmetric electrodes onto the strained TMDs. The scanning photocurrent mapping images follow a fork-shaped pattern, indicating probable conversion of the funneled excitons into electrical currents. In the case of the funnel devices with asymmetric Au and Al electrodes, short-circuit current (ISC ) of WS2 is enhanced by the strains, whereas ISC of MoS2 is suppressed because the Schottky barrier lowers with increasing strain for the MoS2 . These results demonstrate that the funnel devices can be implemented using asymmetrically strained TMDs and the effect of strains on the Schottky barrier is dependent on the TMD used.
Keywords: SU-8 microstructure; asymmetric strain engineering; funnel effect; short-circuit currents; transition-metal dichalcogenides.
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