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

这项研究的目的是生产高效薄膜太阳能电池所需的微晶硅薄膜。作为沉积方法，我们采用了氢自由基化学气相沉积(CVD)的方法，即氢自由基与硅烷分子反应，并影响薄膜的生长表面。我们试图通过研究薄膜的生长过程来控制微晶硅薄膜的结构。首先，为了揭示氢自由基化学气相沉积方法的特点，研究了SiH_4和Si_2H_6作为气体压力和氢的稀释度对硅薄膜的沉积速率、结晶度和电学性质的影响。因此，薄膜的性能。其次，考察了衬底温度(200-350℃)和薄膜厚度(100-100 nm)对薄膜性能的影响。结果表明，在较高的温度下，晶化开始的速度较快，较厚的薄膜的电导率受非晶相特性的影响较大。再次，通过在未掺杂的薄膜上形成双层结构，考察了下层对上层性能的影响。因此，顶层的结晶度和电导率明显取决于底层的表面结构，即使在第二步沉积条件固定的情况下，第一步沉积条件也会影响薄膜的电导率。这一结果表明，两步沉积可以很好地控制薄膜的性能。此外，还发现膜的结构取决于底层和顶层的膜厚。

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.