Blue Femtosecond Laser-Induced Cyrstallization of Amorphous Silicon
從實驗結果可觀察到，在室溫下儘管我們提高脈衝重疊百分比，晶粒的成長大小似乎有一個極限值存在，由實驗結果可知：在室溫時，最大平均晶粒約280 nm，此時所用能量密度為30 mJ/cm2，93.75□的脈衝重疊百分比。
Amorphous silicon (a-Si) was crystallized by femtosecond laser annealing (FLA) using a blue (λ= 400 nm) ultrafast Ti:Sapphire laser system. The line-scan method was applied in the experiment. The intense ultrashort laser pulses lead to efficient nonlinear absorption and the generation of very dense photoexcited plasma in irradiated materials, enabling nonlinear melting on silicon materials. We also study the structural characteristics of recrystallized amorphous silicon films. The grains in the FLA-processed a-Si were found to grow larger as overlapping between irradiated areas was increased up to 89.8% at appropriate fluence. When we increase the overlapping at the same fluence, there will be more energy absorbed by amorphous silicon layer to excite the electrons from valence band to conduction band. Then the annealed amorphous silicon translates into polycrystalline silicon. After increasing the overlapping larger the threshold, the grain size decrease oppositely. We observe that there seems to be a grain size limitation in the room temperature condition even though we increase the overlapping condition. We get the largest grain size is around 280 nm as fluence is 30 mJ/cm2 and overlapping is 93.75□ at room temperature. At last we make comparisons with near-infrared femtosecond laser annealing and excimer laser annealing from the viewpoints of absorption coefficient and penetration depth.
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