The Synthesis Of SiNWs-ZnO Heterojunction Arrays And Their Humidity Sensitivity Studied

Since the 1990s, the synthesis and application of the low dimension nano-materials, especially the one-dimensional semiconductor nanowires, have attracted more and more attention in the fields of physics, chemical, material, information technology and etc. The one-dimensional semiconductor nano materials and their function devices will initialize a new technology revolution and become the center of attention in the 21st century.In this thesis, the preparation of two kinds of new large-area aligned semiconductor nanowires, silicon nanowires (SiNWs) and zinc oxide nanowires (ZnONWs) were investigated, respectively. Special attention had been paid on the preparation processes and the influences of experiment parameters on the synthesis of the SiNWs and ZnONWs. The optimum parameters were determined through the experimental research. Moreover, the humidity sensor based on SiNWs-ZnO heterojunction arrays was prepared and the sensing characteristic of SiNWs-ZnO heterojunction arrays was also investigated. The main works are listed as following:(1) The silicon wafer was etched by the wet chemical etching method and the silicon nanowire arrays were achieved from top to bottom of the Si wafer. The effects of four growth conditions on the morphology of silicon nanowires were discussed, including the concentration of hydrofluoric acid, the concentration of silver nitrate, the etching time and the reaction temperature. Furthermore, the effects of the crystal orientation and resistances of Si wafers on the etching mechanism of silicon nanowires were specially investigated. The experimental data showed that the doping types of Si wafer had not obvious influenced on the formation of SiNWs. The etching orientation of all the nanowires was [100] and the vertical etching rate was decreased with an increase of doping concentration when HF+ AgNCO3 was used as etching solution. In addition, the lengths of SiNWs were found to increase with the increase of the above four growth conditions and the optimum parameters of the synthesis of Si nanowires were determined as that the concentration of hydrofluoric acid was 5 M, the concentration of silver nitrate was 0.02 M, the etching time was 60 min and the reaction temperature was 50℃.(2) The zinc oxide nanowire arrays were synthesized from bottom to top of the Si wafer also by a solution method. The effects of four growth conditions on the growth of zinc oxide nanowires were discussed, including the thickness of seed layer, the concentration of zinc nitrate and hexamethylenetetramine, the reaction time and temperature. The experimental data showed that ZnO nanowires preferred to epitaxial grow along C axle on the ZnO seeds layer and the seeds layer was thicker, the ZnONWs was bigger and closer. The length of ZnONWs added with the concentration of solution and growth time increase. But, the density of ZnONWs became small as the concentration increase. Besides, the nano-tubular structure of ZnO was observed when the growth temperature reached to 90℃.(3) The SiNWs-ZnO heterojunction arrays were obtained by depositing a ZnO layer on the SiNWs arrays, and the highly sensitive humidity sensor based on SiNWs-ZnO heterojunction arrays was packaged and fabricated then. The characteristic curve of humidity sensitivity was measured and the experimental data showed that the moisture sensor based on SiNWs-ZnO heterojunction arrays exhibited higher sensitivity, shorter response/recovery times, better ability to resist hysteresis and longer lifespan than Si-ZnO heterojunction films.In conclusion, the large-area wall-aligned silicon and zinc oxide nanowires could be synthesized by the solution method under relative normal conditions. The humidity sensitivity experiments showed that the SiNWs-ZnO heterojunction arrays are a structure which is sensitive to humidity, and thus will have some potential applications as sensors, such as the moisture sensor.