Morphological Control And Mechanism Study Of Silicon Nanowires Based On Metal-assisted Chemical Etching

Silicon nanowires (SiNWs) have been long considered a promisingmaterial due to their extraordinary electrical and optical properties. As asimple, highly efficient fabrication method for SiNWs, the metal-assistedchemical etching (MACE) has been intensively studied over past years.However, effective control with simple parameter modulation is still achallenging topic and some key questions still remain in the mechanism withinthese processes. Therefore in this work, a systematic study on the morphologymanipulation and related mechanistic process has been carried out. The mainwork is presented as the following:Firstly, the new morphology modulation method of introducing light toMACE process with mechanism study and application researchWe proposed a new light-modulated MACE method and systematicallystudied the influence of illumination power, wavelength and the doping levelof silicon substrate on SiNW’s formation. Not only can conic structuresconsisting of inclined and clustered SiNWs be generated and effectivelymodified by the incident light, but also new patterns such as “bamboo shoot”arrays and “Star” pattern can be formed under certain conditions. Moreimportantly, detailed study has revealed a new top-down “diverting etching”mode of the conic structures in this process other than the previously proposed“bending” model. As predicted, a mass transport of silver particles at the surface etching front has occurred. Evidences suggest relationship of thisphenomenon to the inhomogeneous distribution of the light-induced electronsbeneath the etching front. The experimental method and related mechanismstudy can hopefully open new routes to understand and modulate theformation of SiNWs and other nanostructures.Secondly, the mechanism study based on metal-assisted chemical etchingDifferent doping levels and doping types of silicon substrates wereinvestigated as variables to study its on the deposition of Ag nanoparticles,dendrites and on the morphology and etching rate of silicon nanowires undercertain solution concentration. Also, factors that can lead to the inclination ofSiNWs during MACE process were concluded. A new mechanism regardingthe influence of doping has been proposed combining previous results of theinfluence of H2O2’s concentration on the etching process.