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 l ayers as sensing material. The gas action makes the conductance of the devi ce, measured parallel to the surface between ohmic contacts, decrease. It i s shown how the thickness and the doping level of these layers affect the s ensor sensitivity. A simple model is proposed to describe the gas action, b ased on ionization of chemisorbed NO2 molecules inducing field-effect mecha nism. Calculations lead to thickness, doping level and gas concentration de pendence in agreement with experimental results. The ability for environmen tal applications is also discussed and it is concluded that even if such de vices can detect low NO2 concentrations, they suffer from limitations due t o a parasitic effect of moisture. (C) 1999 Elsevier Science S.A. All rights reserved.