p-Type Conversion of WS₂ and WSe₂ by Position-Selective Oxidation Doping and Its Application in Top Gate Transistors.

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Complementary operation of two-dimensional (2D) material-based field-effect transistors (FETs) requires high-performance p-type FETs.
• Ternary transition metal dichalcogenides like WS2 and WSe2 are promising 2D materials for FET applications.

Purpose of the Study:

• To achieve p-type conversion in intrinsically n-type 2D materials for advanced FET applications.
• To investigate the effectiveness of surface charge-transfer doping using WO3 for p-type FET fabrication.
• To mitigate hysteresis issues in 2D material FETs.

Main Methods:

• Selective surface charge-transfer doping using WO3 (work function ~6.5 eV) on the access region of WS2 and WSe2 FETs.
• Utilizing hexagonal boron nitride (h-BN) to cover the channel region, enabling selective doping.
• Employing top gate (TG) operation with an h-BN protection layer as an insulator.

Main Results:

• Successful p-type conversion of intrinsically n-type trilayer WSe2 FETs by reducing Schottky barrier width and injecting holes.
• Trilayer WS2 did not exhibit clear p-type conversion due to a lower valence band maximum compared to WSe2.
• WO3 doping introduced hysteresis in back-gated WSe2 FETs due to trap sites.
• High-performance p-type WSe2 FETs with negligible hysteresis were achieved using TG operation.

Conclusions:

• Surface charge-transfer doping with WO3 is a viable method for achieving p-type conversion in 2D materials like WSe2.
• Top gate operation with an h-BN insulator effectively suppresses hysteresis in doped WSe2 FETs.
• This work paves the way for high-performance complementary 2D FET circuits.