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

Abstract

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.

Growth, Thermodynamics, and Electrical Properties of Silicon Nanowires

“…Most experimental studies indeed indicate that charge carrier mobilities in silicon nanowires are somewhat smaller than those in bulk Si. [227][228][229][230][231][232][233] There are some studies, however, that report mobilities higher than those in bulk Si. 159,224 A possible explanation for the high mobility values obtained could be the crystallographic orientation of the nanowires.…”

Overview and status of bottom-up silicon nanowire electronics

“…This naturally corresponds to the standard solution widely adopted by semiconductor industry. Interestingly, as discussed in Section 3, doping strategies for bottom-up NWs are not limited to ion-implantation [56,58,104] but alternative methods like in-situ doping [105] or solid-phase post-growth doping [66] are also available. On the other hand, by using a dual gate configuration 1 (see Fig.…”

“…If the device is operated by varying the top-gate voltage at constant back-gate voltage, it should in principle tend to mimic the behaviour of a NW-FET realised with physical doping. Examples of ''conventional-like'' tri-gate NW-FETs using bottom-up Si NW and relying on the physical doping of the channel have been demonstrated via lowfluence ion-implantation [56], in-situ VLS doping using PH 3 [105], and local phase-diffusion from a doped SiO x layer [66]. In addition, Cohen et al achieved similar results by heavily doping a Si buffer layer overgrown on top of a Si NW at the drain and source locations [104].…”

“…Au contamination has also been suggested as a source of non-ideality but the effect of in-growth metal incorporation into Si nanostructures remains controversial to date (as discussed in Section 2). Estimated mobilities were generally lower than in bulk Si [56,104,105]. On one side, this may be related to the errors introduced by incorrect approximation of quantities such as the oxide capacitance or the channel charge, commonly evaluated on the basis of simplified models [20].…”

Mechanical properties of kinked silicon nanowires

“…Recently, SiNWs have been synthesized by different methods such as solution techniques [4] and a metal-catalytic vapor-liquid-solid method [5][6][7]. As potential building blocks for field-effect transistors [8][9][10][11], resonators [12], and biosensing application [13][14][15], SiNWs have been intensively explored. To fabricate novel devices with fewer welding joints and improved electric connections, SiNWs with controlled shape are needed to realize their full potentials.…”