Photoelectric Properties of Funnel Devices Based on Asymmetrically Strained Two-Dimensional Materials

Strain applied to transition metal dichalcogenides (TMDs) decreases their energy bandgap. When local strains are present, a band structure resembling a funnel is created, guiding excitons toward the most strained region. In this study, we present a device with a funnel-like structure based on WS₂ and MoS₂, achieved through asymmetric strains. These strains were induced by transferring TMD flakes onto a fork-shaped SU-8 microstructure. The Raman and photoluminescence spectra peaks were observed to shift based on the morphology of the SU-8 microstructure, confirming the application of asymmetric strains on the TMDs. To examine the potential conversion of funneled excitons into electrical currents, we fabricated various devices by depositing electrodes, both symmetric and asymmetric, onto the strained TMDs. Scanning photocurrent mapping (SPCM) images exhibited a fork-shaped pattern, suggesting the likely conversion of funneled excitons into electrical currents. Specifically, funnel devices with asymmetric Au and Al electrodes demonstrated an enhancement of short-circuit current (I_SC) in WS₂ due to the applied strains. On the other hand, I_SC in MoS₂ was suppressed as the increasing strain lowered the Schottky barrier, unlike WS₂ where the Schottky barrier was not affected by the strain. These findings underscore the potential of utilizing asymmetrically strained TMDs for implementing funnel devices, and emphasize the TMD-specific impact of strains on the Schottky barrier.