Funnel Devices Based on Asymmetrically Strained Transition Metal Dichalcogenides

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 (I-SC) of WS2 is enhanced by the strains, whereas I-SC 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.

Automated summary

The strain applied to TMDs reduces their bandgap and causes a funnel-like band structure with funneled excitons moving towards the most strained region. A funnel device based on asymmetrically strained WS2 and MoS2 is presented, with Raman and photoluminescence shifts indicating the effect of strains. Different devices with symmetric and asymmetric electrodes are constructed to investigate the conversion of funneled excitons into electrical currents. The scanning photocurrent mapping images show a fork-shaped pattern, suggesting the conversion is possible. The effect of strains on the Schottky barrier is dependent on the TMD used, as demonstrated by enhanced short-circuit current for WS2 and suppressed current for MoS2.