Complementary carbon nanotube metal–oxide–semiconductor field-effect transistors with localized solid-state extension doping

Low-dimensional semiconductors such as one-dimensional carbon nanotubes could be used to shrink the gate length of metal–oxide–semiconductor field-effect transistors (MOSFETs) below the limits of silicon-based transistors. However, the development of industry-compatible doping strategies and polarity-control methods for such systems is challenging. Here we report top-gate complementary carbon nanotube MOSFETs in which localized conformal solid-state extension doping is used to set the device polarity and achieve performance matching. The channel of the transistors remains undoped, providing complementary metal–oxide–semiconductor-compatible n- and p-MOSFET threshold voltages of +0.29 V and −0.25 V, respectively. The foundry-compatible fabrication process implements localized charge transfer in the extensions from either defect levels in silicon nitride (SiN_x) for n-type devices or an electrostatic dipole at the SiN_x/aluminium oxide (Al₂O₃) interface for p-type devices. We observe SiN_x donor defect densities approaching 5 × 10¹⁹ cm⁻³, which could sustain carbon nanotube carrier densities of 0.4 nm⁻¹ in the extensions of scaled nanotube devices. Our technique is potentially applicable to other advanced field-effect transistor channel materials, including two-dimensional semiconductors.