Funnel Devices Based on Asymmetrically Strained Transition Metal Dichalcogenides

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Strain engineering in transition metal dichalcogenides (TMDs) is known to modify their electronic properties, including bandgap reduction.
• Local strain gradients can induce unique band structures, such as funnels, that direct charge carriers or excitons.
• Understanding exciton behavior under strain is crucial for developing novel optoelectronic devices.

Purpose of the Study:

• To design and fabricate a funnel device utilizing asymmetrically strained tungsten disulfide (WS₂) and molybdenum disulfide (MoS₂).
• To investigate the conversion of strain-guided excitons into electrical currents within these devices.
• To analyze the impact of asymmetric strain and electrode choice on device performance, specifically short-circuit current (I_SC).

Main Methods:

• Inducing asymmetric strain in WS₂ and MoS₂ flakes by transferring them onto a fork-shaped SU-8 microstructure.
• Characterizing strain application using Raman and photoluminescence spectroscopy, observing peak shifts correlated with microstructure morphology.
• Fabricating devices with symmetric and asymmetric electrodes (Au, Al) on strained TMDs to study photocurrent generation.
• Performing scanning photocurrent mapping to visualize current flow patterns and correlate them with the strained microstructure.

Main Results:

• Raman and photoluminescence spectra confirmed the successful application of asymmetric strains to WS₂ and MoS₂.
• Scanning photocurrent mapping revealed fork-shaped patterns, indicating the conversion of funneled excitons into electrical currents.
• For WS₂, strain enhanced the short-circuit current (I_SC) in devices with asymmetric electrodes.
• For MoS₂, strain suppressed I_SC due to strain-induced lowering of the Schottky barrier with increasing strain.

Conclusions:

• Asymmetrically strained TMDs can be effectively implemented in funnel devices for photocurrent generation.
• The effect of strain on the Schottky barrier and subsequent device performance is highly dependent on the specific TMD material.
• This work highlights the potential for strain engineering in TMDs to tune optoelectronic properties for advanced device applications.