A. M. Rossi

Front-side micromachined porous silicon nitrogen dioxide gas sensor

Abstract In this paper a new C-MOS compatible fabrication process is presented for a nitrogen dioxide porous silicon (PS) sensor. Electrically insulated PS sensing layers and even free-standing PS membranes have been obtained by front side electrochemical micromachining, reducing in this way electrical leakage towards the crystalline substrate. The electrical behavior of the device in a controlled environment was measured by means of a volt–amperometric technique at constant bias. A huge variation of the current was detected at RT for NO 2 concentrations as low as 200 ppb (Δ G / G =111). The interference of humidity, ethanol, methanol, CO and ozone is also discussed.

Towards a Deeper Comprehension of the Interaction Mechanisms between Mesoporous Silicon and NO2

The high sensitivity of a room-temperature porous silicon NO2 sensor has required an investigation of surface dynamics between NO2 and mesoporous silicon. By means of electrical measurements in gas atmosphere and in-situ FTIR, evidence of a new interaction mechanism strongly affecting the electrical conductivity of the porous silicon (PS) sensors has been found. Absorption bands have been attributed to NO2—, suggesting carrier transfer from the silicon wires to NO2, thanks to its high electronic affinity. The models proposed until now, explaining the high resistivity of mesoporous silicon, strongly support this interpretation.

Investigation of the non-radiative processes in porous silicon

The temperature (T) dependence of the yellow-red photoluminescence band is studied in the range from 300 K to 10 K. From the simultaneous intensity and lifetime measurements it is possible to separate unambiguously the radiative and non-radiative components of the decay process. From the analysis of the non-radiative component a model is suggested in which potential barriers can confine excitons, limiting in this way the possible paths for non-radiative recombination.

IR detection of NO2 using p+ porous silicon as a high sensitivity sensor

Mesoporous silicon doped with 3.0 x 10(19) B atoms cm-3 (p(+)-type) is an insulating material which dramatically increases its electrical conductivity when exposed to traces of gaseous NO2; nitrogen dioxide chemisorption at the surface generates carriers, the population of which is readily evaluated through the intensity of IR absorption.