Nanowire-based field-effect transistors (FETs) have demonstrated considerable promise for\na new generation of chemical and biological sensors. Indium arsenide (InAs), by virtue of its high\nelectron mobility and intrinsic surface accumulation layer of electrons, holds properties beneficial for\ncreating high performance sensors that can be used in applications such as point-of-care testing for\npatients diagnosed with chronic diseases. Here, we propose devices based on a parallel configuration\nof InAs nanowires and investigate sensor responses from measurements of conductance over time\nand FET characteristics. The devices were tested in controlled concentrations of vapour containing\nacetic acid, 2-butanone and methanol. After adsorption of analyte molecules, trends in the transient\ncurrent and transfer curves are correlated with the nature of the surface interaction. Specifically,\nwe observed proportionality between acetic acid concentration and relative conductance change,\noff current and surface charge density extracted from subthreshold behaviour. We suggest the origin\nof the sensing response to acetic acid as a two-part, reversible acid-base and redox reaction between\nacetic acid, InAs and its native oxide that forms slow, donor-like states at the nanowire surface.\nWe further describe a simple model that is able to distinguish the occurrence of physical versus\nchemical adsorption by comparing the values of the extracted surface charge density. These studies\ndemonstrate that InAs nanowires can produce a multitude of sensor responses for the purpose of\ndeveloping next generation, multi-dimensional sensor applications
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