In Situ Axially Doped n-Channel Silicon Nanowire Field-Effect Transistors

Axially doped (n(+)-p(-)-n(+)) silicon nanowires were synthesized using the vapor-liquid-solid technique by sequentially modulating the introduction of phosphine to the inlet gas stream during growth from a silane source gas. Top-gate and wrap-around-gate metal oxide semiconductor field-effect transistors that were fabricated after thermal oxidation of the silicon nanowires operate by electron inversion of the p(-) body segment and have significantly higher on-state current and on-to-off state current ratios than do uniformly p(-)-doped nanowire field-effect devices. The effective electron mobility of the devices was estimated using a four-point top-gate structure that excludes the source and drain contact resistance and was found to follow the expected universal inversion layer mobility versus effective electric field trend. The field-effect properties of wrap-around-gate devices are less sensitive to global-back-gate bias and thus provide better electrostatic control of the nanowire channel. These results demonstrate the ability to tailor the axial doping profile of silicon nanowires for future planar and vertical nanoelectronic applications.