Fabrication of microcrystalline silicon thin films for high-efficiency solar cells by using high-density hydrogen radicals

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The purpose of this, study, is to produce microcrystalline silicon films necessary for high-efficiency thin film solar cells. As deposition method, we used a hydrogen radical CVD, method in which hydrogen radicals react with silane molecules as well as affect the growing surface of films. We tried to control structure of microcrystalline silicon films by examining the growing process of thin films.First, to reveal the characteristic of the hydrogen radical CVD method, deposition rate, crystallinity and electrical properties of silicon films were investigated using SiH_4 and Si_2H_6 as a function of gas pressure and hydrogen dilution. As a result, film properties. Could be changed from amorphous to microcrystalline by these experimental parameters.Secondly, dependences of film properties on substrate temperature (200-350℃) and film thickness (100-lOOOnm) were examined. It was shown that at higher temperature crystallization starts at a faster stage and that in thicker films the electrical conductivity is more affected by the characteristic of amorphous phase.Thirdly, effect of lower layer on upper layer' properties was examined by forming a double layer structure with a P-doped layer on an undoped layer. Consequently, the crystallinity and electrical conductivity of top layer depended clearly on the surface configuration of bottom layer.electrical conductivity of deposited silicon films were affected by first-step deposition conditions even if second-step deposition conditions were fixed. This result indicates that film properties can be controlled well by two-step deposition. Moreover, film structure was found to depend on both film thicknesses of bottom and top layers.