NO2 detection by a resistive device based on n-InP epitaxial layers

This paper deals with a new type of NO2 sensor using n-type InP epitaxial layers as sensing material. The gas action makes the conductance of the device, measured parallel to the surface between ohmic contacts, decrease. It is shown how the thickness and the doping level of these layers affect the sensor sensitivity. A simple model is proposed to describe the gas action, based on ionization of chemisorbed NO2 molecules inducing field-effect mechanism. Calculations lead to thickness, doping level and gas concentration dependence in agreement with experimental results. The ability for environmental applications is also discussed and it is concluded that even if such devices can detect low NO2 concentrations, they suffer from limitations due to a parasitic effect of moisture. (C) 1999 Elsevier Science S.A. All rights reserved.