Study On Ethanol Gas Sensor Based On Fabry-Pérot Interference Effects Of Porous Silicon

Alcohol is volatile,belonging to the flammable gas and easily exploded in the air. So it is necessary to monitor alcohol concentration in the industry production and road transportation. At present the common used alcohol sensor is fuel cell type and semiconductor type, with weakness being either high price or poor selectivity and demanding the heat device. Therefore it is very significant to develop the sensor of low price,high sensitivity and selectivity,detecting lower alcohol concentration. The main advantages of porous silicon gas sensor are higher sensitivity and selectivity without heating in the room temperature,high measure precision and low price. Based on the former work of our team, p-type silicon wafer is used as the start material to prepare porous silicon film by electrochemical anodic oxidation, then a steady photoluminescence PS is obtained by surface passivation. It is expected to get a functional PS material which is anti-oxidized in the air and excellent sensing property to alcohol. The main points of this dissertation are as following:(1) It is summarized that the current studies situation, preparation mechanism, stabilizing treatment, physicochemical properties, and applied research status for detecting of porous silicon.(2) Porous silicon was prepared by the pulsed electrochemical anodization method. The influences of different electrochemical conditions on the Fabry-Pérot (F-P) interference characteristic of porous silicon were investigated. The optimal condition to prepare the PS for alcohol detecting is presented: duty cycle 5:10, current density 78mA·cm^-2, effective anodization time 5 min, electrolyte HF/C₂H₅OH=2:1(V/V). The property of the films prepared under the conditions is very stable and the interference fringes are uniform.(3) The structure and the physicochemical properties were characterized, including the porosity, thickness of the PS film, the surface and the profile morphology. The porosity increased with the increasing current density. However, prolonging the anodization time lead to the porosity first increased and then decreased. The porosity reached a maximum value of 56.8% when the anodization time was 5 min. Increasing the concentration of HF could induce the porosity decreased. The film thickness existed a prositive correlation with current density, anodization time and the concentration of HF. (4) The qualitative and quantitative study of sensing alcohol were developed on the porous silicon with Fabry-Pérot (F-P) interference characteristic. The sensing mechanism was discussed and the response time was obtained, as well as the sensing reversibility. The reflectance spectra of the porous silicon were red-shifted(～25nm) and the corresponding optical thickness (OT) increased(～430nm) when exposed to a certain concentration of alcohol(500ppm). There is a positive correlation betweenΔOT and the concentration of alcohol, namely theΔOT increased with the increasing concentration of alcohol and the selectivity and reversibility were getting better. The response time for detecting alcohol at low concention was less than 1 min.