Study On The Gas-sensing Properties Of WO₃thin Films Composited Of Ordered Porous Silicon

Nowadays with the development of industry technologies as well as theenhancement of people’s environmental awareness, people begin to pay more andmore attention on the research of gas sensors. As a type of gas-sensing materialaround room temperature, porous silicon is widely studied and used as a low-powergas sensor at room temperature because of its simple preparation methods andunique microstructure; while tungsten oxides is also getting more and more attentionsfor the good gas-sensing properties. This paper mainly focuses on the preparation andgas-sensing properties tests of n-type ordered porous silicon, on the basis of which wecomposite WO3thin films with n-type ordered porous silicon, test their gas-sensingproperties, and discuss about the gas-sensing mechanisms.N-type porous silicon is prepared using the two-cell electrochemical method withpore diameter ranging from50to200nm, after which the gas-sensing properties aretested. The results are as follows: the pore diameter and depth of porous silicon willgrow larger with the increase of current density; when the current density is smallenough the main pores will branch; when the current density is120mA·cm-2we getordered porous silicon with smooth pore walls; when the current density is more than140mA·cm-2the silicon substrate will get electropolished; the depth of porous silicongrows larger with the increase of time while the pore diameter grows wider and porewalls become smoother. The sensitivities of the sample to1ppm NO2and50ppm NH3are3.37and5.09respectively, which is prepared under120mA·cm-2for25min.WO₃thin films are sputtered on the surface of ordered porous silicon to formcomposite structure, after which the gas-sensing properties are tested. Theexperiments show that the sensitivity of the sample to1ppm NO2is as high as19.14,whose sputtering time is10min. And the composite structure shows higher sensitivityto NO2than NH3and other organic vapor. The abnormal resistance change ofcomposite structure after absorbing NO2could be due to the inversion layer aroundthe surface of WO3thin films. There exist a lot of defects and surface states aroundthe heterojunctions after the composition of WO3thin films and porous silicon, whichshould be responsible for the increase of sensitivity to NO2.