Ultrathin BiOx Charge-Transfer Doping for Cross-TMD Electronic Modulation and Homogeneous WSe2 Inverters

Charge-transfer doping provides a nondestructive route to tune two-dimensional transition-metal dichalcogenides (TMDs), but selectively patterned n-type dopants effective across different TMD channels remain limited. Here, ultrathin bismuth oxide (BiOx) is used as an n-type charge-transfer doping and passivation layer for monolayer MoS2 and WSe2 transistors. In MoS2, 2 nm BiOx preserves the channel structure and yields a TLM-extracted effective contact resistance of 0.71 ± 0.06 kΩ·μm at n2D = 1.8 × 1013 cm-2. Thicker BiOx strengthens n-type modulation but reduces gate controllability. The modulation remains stable after ambient storage and air annealing. BiOx also enhances electron transport in WSe2 and enables homogeneous WSe2 inverters with MoOx-doped p-FETs, achieving a gain of ∼19 and a total normalized noise margin of 0.895 VDD at VDD = 2 V. These results establish BiOx as a cross-TMD n-type charge-transfer dopant for contact, threshold-voltage, and polarity engineering.