High-Performance p-Type Black Phosphorus Transistor with Scandium Contact

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Black phosphorus (BP) is a promising 2D material for next-generation electronics due to its high carrier mobility.
• Understanding the impact of processing and environmental factors on BP transistor performance is crucial for device fabrication.
• Metal contact engineering is vital for optimizing charge injection and transport in BP devices.

Purpose of the Study:

• To investigate the effects of vacuum annealing and Al2O3 capping on the electrical performance of black phosphorus transistors.
• To elucidate the influence of moisture on black phosphorus metal contacts.
• To determine the optimal black phosphorus film thickness for transistors with scandium contacts.

Main Methods:

• Fabrication and characterization of few-layer black phosphorus transistors with scandium and gold contacts.
• Electrical measurements under various conditions: as-fabricated, vacuum annealed, and Al2O3 capped.
• Analysis of device performance metrics including current density, on/off ratio, subthreshold swing, and hysteresis.

Main Results:

• A record current density of 580 μA/μm was achieved for BP transistors with scandium contacts after 400 K vacuum annealing.
• Vacuum annealing improved on-state current and Ion/Ioff ratio by one order of magnitude and subthreshold swing by ~2.5×.
• Al2O3 capping degraded transistor performance, reducing on-state current and Ion/Ioff ratio by 5× and 3×, respectively.
• Optimal BP film thickness for scandium contacts was found to be ~10 nm.
• All transistors with scandium contacts exhibited p-type behavior, indicating Fermi level pinning near the valence band.

Conclusions:

• Vacuum annealing is a highly effective method for enhancing the performance of black phosphorus transistors with scandium contacts.
• Al2O3 capping negatively impacts BP transistor performance, suggesting sensitivity to dielectric interfaces and potential degradation pathways.
• Scandium contacts promote stable p-type behavior in black phosphorus transistors, irrespective of flake thickness, simplifying device design and operation.