| Porous Silicon is widely applied in kinds of sensors with the characteristics of good insulation, gas sensing in the low temperature, the emitting and electrical insulation. With the rapid development of MEMS technology, the porous silicon has great application prospect.Porous silicon （PS） layers were obtained by electrochemical etching; two methods were used to improve the gas-sensing performance of the porous silicon gas sensor. One was putting the sensor under the ultraviolet irradiation. The other was the use of the traditional doping process. The gas-sensing performance was studied under different concentrations of NO2, which makes a foundation for widely use.Under the irradiation of UV, the initial resistance of PS decreases quickly. The sample with an etching current density of 80mA/cm2 has the largest change. The photo-generated charge efficiency increases in the sequence: PS-40<PS-60<PS-80 and this sequence is consistent with the increase of the porosity, which means the increase of surface-to-volume ratio. It has been demonstrated that the sensitivity to NO2 was enhanced with the UV irradiation compared with that without irradiation and the sensing character of PS-80 owns the largest influence under the illumination of UV. At the same time, the response and recovery character to NO2 of porous silicon gas sensor improved under the UV irradiation.TiO2 or WO3 films were deposited on porous silicon substrates by reactive DC magnetron sputtering to fabricate the porous silicon gas sensor. According to the image of SEM, they are structures with lots of coherent channel. The result of measurement showed a much higher response value and faster response characteristics to NO2 gas with TiO2 or WO3 doped under room temperature.PS with WO3 doped has the best NO2 gas sensing. It shows a high sensitivity of 27.8 to 2ppm of NO2, and the sensor response time is about 5sec. But, the recovery time of the sensor with WO3 doped is longer than the other samples. |
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