From Amorphous-Si Thin-Film-Transistors to Single Crystal-Si Transistors: Influence of Si Crystallinity on Device Properties

摘要

Silicon, under its various phases from amorphous (a-Si:H) to monocrystalline, with intermediates microcrystalline (μx-Si:H) and polycrystalline, can be used to manufacture devices with very different characteristics. We have investigated some links between device characteristics and material crystallinity. Carrier mobility is strongly dependant on defects with energy levels within the semiconductor bandgap, and these defects are reduced when crystal order is increased. The reduced drain leakage current in a-Si:H in comparison with microcrystalline (μc-Si:H) Thin-Film Transistors (TFTs) is explained by differences in material properties related to crystallinity. Finally, it is shown that μc-Si:H TFTs exhibit better threshold voltage (V_(th)) stability than a-Si:H ones. Investigation of V_(th) drift mechanisms indicates that this is related to improvement of the semiconductor material quality.