Controllable Growth And Graphical Preparation Of Silicon Nanowires

The photoelectric properties about silicon nanowires with the characteristics ofdirect band gap semiconductor are very outstanding. For this reason, the siliconnanowires have a promising application prospect in the field of photovoltaic devicesand sensing devices.The controllable morphology and designated position growthare very important to the Si nanowires’ device application. Ag-catalyzed etchingmethod, which is also known as two-step method, is used to prepare SiNWs atnormal temperatures and pressures. The concrete preparation process is as follow:The clear Si wafer should be H-terminated before immersing in the solution with4.8mol/L HF and0.01mol AgNO₃to deposit silver particles. After Ag deposition step,Si wafer is etched in the oxidizing solution with4.8mol/L HF and0.4mol/L H₂O₂.The silver particles can be removed by diluent HNO₃. The characteristics of SiNWsmorphology changes are studied by means of adjusting experimental parameters.EDS, XRD, UV, FTIR, Raman, PL are used to characterize the properties of SiNWs.Si nanowres grow on the designated position could be carried out by thetechnology of surface graphical pretreatment and Ag-catalyzed etching method. Thecontrollable growth and graphical preparation of Si Nanowires are disscussed infollowing ways:Firstly, two different types of Si wafers are used to prepare SiNWs. Themorphology differences of them are analysed, subsequently. The reasons of thedifferences are discussed. Influence characteristics of SiNWs morphology with P（100） silicon, caused by silver depositon time, etching time, etching temperture,AgNO₃concentration, H₂O₂concentration and HF concentration, are focused on.Secondly, P （100） type silicon wafer is used to prepare SiNWs by one-stepmethod. In this method, Si wafer is directly immersed in the solution containing HFand AgNO₃for a period of time. The etching result of one-step method is comparedwith two-step method’s. The similarities and differences, caused by HF/Fe（NO₃）₃etching system and HF/H₂O₂etching system during the SiNWs preparation, areanalysised. Observing the locations of silver particles after different etching time,the Ag particles etching silicon’s way is confirmed.Lastly, a layer of Si3N4thin film is deposited on P （100） type silicon surface byLPCVD. Photolithography is then applied to etch windows with different shapes andsizes. Silicon is inside the window, Si3N4is outside the window. SiNWs emerge inthe windows by two-step method. SiNWs growing on specific location is realized byabove way.