Applications

Nanocrystalline Si (nc-Si:H) thin films prepared by PECVD or HWCVD are a candidate for electronic and photovoltaic applications such as thin-film transistors (TFTs) (see, e.g., [37]) and solar cells. Nanocrystalline Si solar cells are more stable than a-Si:H-based solar cells [38, 39], since nc-Si:H is relatively free from light-induced degradation. Taking p-i-n structure, the open circuit voltage Voc is achieved to be 600 meV and the efficiency is approaching 10% [40, 41].

The applications of TFTs in large-area flat panel displays are very attractive using Si thin films. TFTs based on hydro-genated amorphous silicon films (a-Si:H) have been used in massive produced displays and sensor arrays. Although the mobility (TFT mobility) of a-Si:H TFTs is low (~1 cm2-V-1 s-1), they are suitable as the pixel switches in active matrix liquid crystal displays. This is due to a capability of fabrication with low cost and large area (>15 in), with high yield and very uniform performance. To get high-resolution displays, larger electron mobility should be required in the pixel TFTs. The major drawbacks for a-Si:H-based TFTs are (i) low electron mobility and (ii) low stability: the threshold voltage Vth shifts with successive switching. The TFT mobility using nc-Si:H is reaching ~20 cm2 V-1 s-1 and higher stability is reported. Note that the TFT mobility in polycrystalline Si by pulsed laser crystallization (PLC) is reported to be ~600 cm2 V-1 s-1 [20]. The challenge to get higher mobility and higher stability in nc-Si:H films is continuing.

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