Polycrystalline silicon films have been deposited on glass substrates at 350 °C by radio-frequency plasma-enhanced chemical vapor deposition using a SiF4+H2 gas mixture. Crystalline fraction decreased abruptly with increasing gas flow ratio. Film structure drastically changed by increasing gas pressure from 0.4 to 2.0 Torr. At lower gas pressure, columnar crystals 30 nm in diameter grew from the glass substrates, while at higher gas pressure larger columnar crystals with a maximum diameter of approximately 100 nm grew on an amorphous Si layer approximately 170 nm thick.
The local structure and crystallization of amorphous GeTe (a-GeTe) were examined by means of Ge K-edge EXAFS. In a-GeTe, both Ge-Ge and Ge-Te bonds were observed to exist in nearest neighbors of Ge. The average coordination number around Ge is 3.7, which is close to the tetrahedral structure. A random covalent network (RCN) model seems to be suitable for the local Structure. After a-GeTe crystallizes at 129°C, the Ge-Ge bond disappears and the Ge-Te bond length increases considerably. As temperature rises, in a-GeTe the Debye-Waller factor of the Ge-Te bond increases greatly, while that of the Ge-Ge bond increases only slightly. At the crystallization, it is found that the fluctuation of the Ge-Te bond length plays a major role in the change of the local structure and bonding state around Ge.
The etching of hydrogenated amorphous silicon (a-Si:H) in thermally generated atomic hydrogen has been investigated in detail, utilizing real time spectroellipsometry for characterization and end-point detection. When properly controlled, etching can yield ultrathin microcrystalline Si (μc-Si:H) films of relatively high density on virtually any substrate material. These films are unique in that their microstructure is established by the crystallization of the near-surface a-Si:H, rather than by the nucleation of crystallites on the substrate, as occurs for plasma-enhanced chemical vapor-deposited μc-Si:H films.
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