N-type in-situ doping effect on vapour-liquid-solid silicon nanowire properties for gas sensing applications

N-type in-situ doped SiNWs based resistors are fabricated and used as gas (ammonia) sensors. SiNWs are prepared by vapour-liquid-solid method (VLS) using gold as catalyst. In-situ doping level is adjusted by varying the phosphine to silane mole ratio. Because SiNWs can act as sensitive units specific design is developed to allow large sensing areas, following a process fabrication compatible with a mass production planar layout. SiNWs doping effect on ammonia detection is carried out under controlled ammonia/nitrogen mixture varying from 2 ppm to 700 ppm. Results highlight that the relative response, S-g=(I-0-I-g)/I-0, where I-0 and Ig are the current values in vacuum and reactive ambient respectively, follows a linear behaviour. The relative sensitivity, (S=Delta S-g/Delta[NH3]) decreases, whereas the sensitivity (SxI(0)) increases with the increase of the VLS SiNWs doping level. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim