Hydroxylation-driven Type-I to Type-II band alignment transition in WS₂/m-plane ZnO heterostructures

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Two-dimensional transition-metal dichalcogenides (TMDs) integrated with wide-bandgap semiconductors are key for advanced optoelectronics.
• The WS2/ZnO heterostructure offers potential for high-efficiency light-emitting diodes (LEDs) due to its Type-I band alignment.

Purpose of the Study:

• To investigate the impact of water adsorption and hydroxylation on the WS2/ZnO interface's optoelectronic properties.
• To understand how surface modifications affect the band alignment crucial for LED performance.

Main Methods:

• First-principles calculations using the HSE06 hybrid functional.
• Analysis of electronic structure, band alignment, and charge transfer using Bader charge analysis.

Main Results:

• Surface hydroxylation converts the desirable Type-I band alignment to a less efficient Type-II alignment, reducing LED recombination efficiency.
• Hydroxylation shifts the conduction band offset by ~1.3 eV, causing spatial separation of electrons and holes.
• Localized hydroxylation induces in-gap states, leading to exciton localization.

Conclusions:

• Surface water adsorption significantly alters the WS2/ZnO interface, detrimentally impacting LED efficiency.
• The ability to tune band alignment from Type-I to Type-II via surface modification opens possibilities for other optoelectronic devices like photodetectors.