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. Author manuscript; available in PMC: 2011 Feb 10.
Published in final edited form as: Nano Lett. 2010 Feb 10;10(2):547. doi: 10.1021/nl9034219

Figure 1.

Figure 1

Screening length effect on the operation and sensitivity of NW FET sensors. The working regime and effectiveness of gating effect induced by molecules at surface of NW-FET sensors are determined by the relative magnitude between carrier screening length λSi and nanowire size (radius) R. In the high carrier concentration regime where λSi≪R, NW-FET works in the linear regime, where the conductance G varies with gate voltage linearly. In the low carrier concentration regime where λSi≫R, NW-FET works in the depletion (subthreshold) regime where the G varies with gate voltage exponentially. In the linear regime, the field effect of positive/negative surface charges induces band bending and carrier depletion/enhancement inside the NW within a region of depth ∼ λSi. The amount of band bending at the NW surface is also denoted as surface potential shift ΔϕSi. In the subthreshold (depletion) regime, carriers in NW have long screening length (λSi ≫R) and the field effect of surface charges can gate the whole NW, fully utilizing the high surface volume ratio of NW. In this case, the Fermi level EF is shifted by ΔϕSi relative to the band edges throughout the whole cross-section of NW.