掺硼nc-Si:H薄膜中纳米硅晶粒的择优生长

Preferred growth of nanocrystalline silicon in boron-doped hydrogenated nanocrystalline silicon films

利用等离子体增强化学气相沉积(PECVD)生长的系列掺硼氢化纳米硅(nc-Si:H)薄膜中纳米硅晶粒(nanocrystallinesilicon,简称nc-Si)有择优生长的趋势。用HRTEM、XRD、Raman等方法研究掺硼nc-Si:H薄膜的微观结构时发现:掺硼nc-Si:H薄膜的XRD只有一个峰,峰位在2θ≈47o,晶面指数为(220),属于金刚石结构。用自由能密度与序参量的关系结合实验参数分析掺硼nc-Si:H薄膜择优生长的原因是:适当的电场作用引起序参量改变,导致薄膜在适当的自由能范围内nc-Si的晶面择优生长。随着掺硼浓度的增加,nc-Si:H薄膜的晶态率降低并逐步非晶化。nc-Si随硅烷的稀释比增加而长大,但晶态率降低。nc-Si随衬底温度升高而长大,晶态率提高。nc-Si随射频功率密度的增大而长大,晶态率增大的趋势平缓。但未发现掺硼浓度、稀释比、衬底温度、射频功率密度的变化引起薄膜中nc-Si晶面的择优生长。

Series of Boron-doped hydrogenated nanocrystalline (nc-Si:H) films were prepared with Plasma Enhanced Chemical Vapor Deposition (PECVD) system by rf(13.59 MHz) and dc bias stimu-lation. Its microstructure was investigated by using High Resolution Transmition Electron Microscope(HRTEM), X-ray Diffraction (XRD) Meter and Raman Spectrum Meter. The preferred growth of nc-Si in the Boron-doped films is found. The peak of XRD spectrum is at 2θ≈47o and the index of crystalline plane is (220). The reason is considered as following, the electric field derived from dc bias makes the bond of Si-Si to array in certain direction. The size of nc-Si and crystalline volume fractionare strongly depended on the deposited parameters: boron concentration, hydrogen concentration, rf power density and substrate temperature. But the preferred growth of nc-Si in the boron-doped nc-Si:H films can only be realized by dc.bias.