Abstract:
A fast responding NO2 sensitive device operating at room temperature has been
realized using the nanolayered amorphous Te (a-Te) grown onto insulating wafer of
silicon dioxide (SiO2) between Pt contact electrodes with larger thickness in a planar
arrangement. The structure of the fabricated sensor has been investigated by AFM and
SEM but its characterization was realized via studying the current - voltage
characteristics, dynamic response, long – term stability and effect of humidity.
Explanation of obtained results is given in terms of a model based on simultaneous
involvement of contact and surface phenomena for the gas sensing. As the Pt electrode
work function (5.43 eV) exceeds the respective value of a-Te (5.03 eV) the ohmic contacts
are formed and the current flow is controlled exclusively by bulk resistance of a-Te
nanolayer that is known to be controlled by type and concentration of toxic gas of the
ambiance. Wherein, as the energetic forbidden gap of a-Te (0.33 eV) is less than the work
function difference between contacting materials, at the contacts can arise the degenerate
regions of p-type metallic Te, as well as geometric contact gaps originated from
microscopically roughness. The gas adsorption inside these contacts gaps leads to
increasing the portion of the semiconducting a-Te nanolayer turned into metal of p-type
Te and consequently to a fast increasing of the current.