NO2 monitoring at room temperature by a porous silicon gas sensor

A study on reactivity of p(+) porous silicon layers (PSL) to different gas atmosphere has been carried out. Substrate doping was 5-15 m Omega cm and 0 .5 Omega cm, porosity ranged from 30 to 75% and the thickness of the porous layers was 20-30 mu m. Three different processes to insure good electrical contact are proposed and discussed. PSL were kept at constant bias and cur rent variations due to interaction with different concentrations of NO2 wer e monitored at constant relative humidity (R.H.). Measurements were perform ed at room temperature (R.T.) and at atmospheric pressure. Concentrations a s low as 1 ppm were tested, but the high sensitivity of the sensor makes po ssible to test lower values. The recovery time of the sensor is of the orde r of one minute. Response to interfering gases (methanol, humidity, CO, CH4 , NO, NO2) has been examined also. In-situ FTIR spectroscopy in NO2 atmosph ere shows a fully reversible free-carrier detrapping in the IR region. conf irming the validity of the models proposed in the recent past for electrica l conduction in mesoporous silicon. (C) 2000 Elsevier Science S.A. All righ ts reserved.