Highly end-doped siliconnanowires for field-effect transistors on flexible substrates

Abstract

We report on the VLS (vapour–liquid–solid) fabrication and characterization of in situ axially doped silicon nanowires (SiNWs) at both ends, and on their integration into a bottom gate–top contact geometry on both rigid and flexible substrates to realize field-effect transistors (FETs). To improve contact resistance between SiNWs and source/drain electrodes, we axially tuned the level of doping at both ends of the SiNWs by sequential in situ addition of PH₃. Characterisation of SiNWs by scanning spreading resistance microscopy in the device configuration allowed us to determine precisely the different sections of the SiNWs. The transfer to flexible substrates still allowed for workable FET structures. Transistors with electron mobilities exceeding 120 cm² V⁻¹ s⁻¹, I_on/I_off ratios greater than 10⁷ and ambipolar behaviour were achieved.