Heterojunction gas sensors for environmental NO2 and CO2 monitoring

The NO2 and CO2 sensing properties of a heterojunction gas sensor formed be tween n-type ZnO and a p-type composite based on a mixture of BaTiO3/CuO/La 2O3 have been evaluated and compared with the performance of its component p- and n-type materials. It was found that the individual ZnO and BaTiO3/Cu O/La2O3 sensors showed resistance increases when exposed to NO,. When expos ed to CO2, the ZnO based sensor showed no response, while the BaTiO3/CuO/La 2O3 sensor showed a small resistance increase. The heterojunction sensor wa s found to be insensitive to < 3000 PPM CO2 although at higher concentratio ns it showed a small decrease in resistance. The resistance also decreased when exposed to low levels of NO2, indicating that a different detection me chanism was operative at the heterocontact compared with the single-phase m aterials. (C) 2001 Elsevier Science Ltd. All rights reserved.