Etching Of Ordered Silicon Nanowires Arrays For Gas Sensing Applications

With the development of industry,many kinds of gases in society emerge more and more frequently,especially the gases which is toxic for human body like NO_x?NH₃ and the volatile organic compounds.So it is necessary to detect these gases accurately and reliably.Traditional gas sensor usually has a work temperature of far above room temperature,and its system seems too big to integrate.So it has importance to explore a gas sensor which can work in room temperature and has abilities of miniaturization and integration.The silicon nanowire?SiNW?gas sensors which are available now usually work in room temperature,but they have limited sensitivity values,and the preparation of them usually need complex process technology or cost too much,these disadvantage limited the silicon nanowire gas sensors'mass application.This paper obtained straight-aligned silicon nanowire arrays through a simple and low cost way that is so called one step metal-assisted chemical etching?MACE?.The morphology influence of etchant concentration and etching time was investigated through scanning electron microscope?SEM?.We achieved a set of best etchant concentrations and etching time.We study the gas sensing properties'differences of silicon nanowires which we have prepared and been deposited by three kinds of metal particles.We observed that silicon nanowire gas sensors which are modified with Cu,Ti and w by magnetron have increasing performance in sensitivity,response and recovery time than the gas sensors which are consisted of pure silicon nanowires to 5ppm NO₂ to a various extent.We developed a kind of anisotropy second etching method which can significantly improve silicon nanowires'active surface area,that is we use anisotropy etchant KOH to to etch the silicon nanowires in the next step,and a rougher surface is observed.Specific surface area value is obtained from a BET method.The value is ten times to the silicon nanowires before KOH etching.We use SEM and TEM to characterize the morphology the diameter of nanowire is decreased,and the cluster is smaller.Effect of the second etching time is investigated,and we observed that when the etching time is 20s,the gas sensor showed the best sensitivity to 100ppm H₂.We tested the rough SiNW array-based sensor'sensing properties to H₂ from the concentration of 50ppm to 10000ppm.Consequently,the rough SiNW array-based sensor exhibited considerable gas sensitivity and a linear response with a wide range of concentrations?50–1000 ppm?at room temperature.Good stability and selectivity,satisfying response–recovery characteristics were also achieved.Then we tested a kind of oxidation gas-NO₂.As a result,the sensor based on the rough SiNWs array exhibits higher sensitivity and better response-recovery response time than the smooth ones.In a word,this paper provide a new anisotropy second etching method,and it is an effective way to improve the silicon nanowires'gas sensing properties at room temperature.