P-type electrical contacts for 2D transition-metal dichalcogenides

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Digital logic circuits rely on complementary metal oxide semiconductor (CMOS) technology using n- and p-type field-effect transistors (FETs).
• Achieving controllable p-type doping in low-dimensional semiconductors, particularly two-dimensional (2D) transition-metal dichalcogenides (TMDs), remains a significant challenge.
• Existing methods struggle to create effective p-type devices using high-work-function metals on 2D TMDs, despite success with n-type contacts.

Purpose of the Study:

• To develop high-performance p-type field-effect transistors (FETs) on 2D transition-metal dichalcogenides (TMDs).
• To investigate the interface properties between 2D TMDs and high-work-function metals for p-type device fabrication.
• To demonstrate the potential of these p-type TMD devices in electronic and optoelectronic applications.

Main Methods:

• Industry-compatible electron beam evaporation of high-work-function metals (palladium and platinum) onto single- and few-layered molybdenum disulfide and tungsten diselenide.
• Atomic resolution imaging and spectroscopy to analyze the van der Waals (vdW) interfaces.
• Electronic transport measurements to characterize device performance, including contact resistance, mobility, and on/off ratio.

Main Results:

• High-performance p-type FETs fabricated on 2D TMDs with near-ideal vdW interfaces, free from chemical interactions.
• Demonstrated low contact resistance (3.3 kΩ·µm), high mobility (~190 cm²/V·s), and excellent on/off ratio (10⁷).
• Successfully fabricated an ultra-thin photovoltaic cell with a 0.6 V open-circuit voltage and 0.82% power conversion efficiency.

Conclusions:

• Controllable p-type doping and high-performance devices are achievable in 2D TMDs using specific metal contacts and fabrication techniques.
• The developed vdW contacts offer a promising route for advancing 2D electronics and optoelectronics.
• This work overcomes a critical hurdle in realizing the full potential of 2D materials for next-generation electronic applications.