Crystallization of Amorphous Silicon with Clean Surfaces

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Abstract
Crystallization of amorphous Si (a-Si) on SiO2 layers in ultra-high vacuum (UHV) was examined by transmission electron microscopy (TEM) and reflection high energy electron diffraction. The SiO2 growth, the a-Si deposition on the SiO2 layer, and the annealing for the crystallization were successively carried out in a UHV molecular-beam-epitaxy chamber. It has been found that the initial nucleation and the grain growth occur at the surface of the a-Si layer, in contrast with the nucleation at the a-Si/SiO2 interface ordinarily observed in the previous studies. Cross-sectional TEM observations revealed a novel mode of crystallization which resulted in the formation of mushroom-shaped Si grains at the a-Si surface. The mechanism of the crystallization was also discussed.