The Study Of Nano-Crystalline Silicon Thin Film In Hot-Wire Chemivcal Vapor Deposition (HWCVD)

Silicon thin film solar cells mainly include hydrogenated amorphous silicon (a-Si:H) solar cells, microcrystalline silicon solar cells, polycrystalline silicon solar cells and tandem or triple junction solar cells made of these materials. As the second-generation solar cells, silicon thin film solar cells have the advantage of abundant raw materials, low cast, easy to deposit in large area. This thesis mainly research boron doped hydrogenated nano-crystalline silicon prepared by hot-wire chemical vapor deposition(HWCVD).In this paper, we research the doped property of thin films deposited by tungsten diameters of 0.3mm under various parameters, and the effect of tungsten filament with the diameter of 0.2mm and 0.3mm on property of nano-crystalline thin films.First of all we research the doped property of thin films deposited by tungsten diameters of 0.3mm under filament temperature=1800℃.We have changed the ratio of diborane in gas, substrate temperature and the deposition pressure, then discuss the change of deposition rate, crystalline volume fraction, dark conductivity and carrier concentration of thin films. The results revealed that dark conductivity and carrier concentration of thin films have the maximum under ratio of diborane in gas=7%, substrate temperature=220℃,deposition pressure=50Pa separately. Considering the results of crystalline volume fraction and deposition rate,this can be explained by catalysis cracking BH3 radicals on thin film surface and the interaction between BH3 and silicon dangling bonds on surface.We report the property of nano-crystalline thin films deposited by tungsten filament with the diameter of 0.2mm and 0.3mm, under filament temperature=1800℃. Deposition rate, crystalline volume fraction and dark conductivity demonstrate that because tungsten filament with the diameter of 0.3mm has larger surface area than 0.2mm, so hydrogen termination of Si dangling bonds on surface is larger, this causes the enhancement of BH3 radicals physisorption and SiH3 radicals migration on surface, so deposition rate and crystalline volume fraction of thin films deposited by 0.3mm diameter tungsten are larger than 0.2mm diameter, and dark conductivity of thin films is smaller than 0.2mm diameter tungsten.