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.

Use of phosphine as an n-type dopant source for vapor-liquid-solid growth of silicon nanowires.

Phosphine (PH3) was investigated as an n-type dopant source for Au-catalyzed vapor-liquid-solid (VLS) growth of phosphorus-doped silicon nanowires (SiNWs). Transmission electron microscopy characterization revealed that the as-grown SiNWs were predominately single crystal even at high phosphorus concentrations. Four-point resistance and gate-dependent conductance measurements confirmed that electrically active phosphorus was incorporated into the SiNWs during VLS growth. A transition was observed from p-type conduction for nominally undoped SiNWs to n-type conduction upon the introduction of PH3 to the inlet gas. The resistivity of the n-type SiNWs decreased by approximately 3 orders of magnitude as the inlet PH3 to silane (SiH4) gas ratio was increased from 2 x 10(-5) to 2 x 10(-3). These results demonstrate that PH3 can be used to produce n-type SiNWs with properties that are suitable for electronic and optoelectronic device applications.