(Once again, all references are to MRS paper numbers, abstracts for which can be found at the conference site.)
Today at the MRS Spring Meeting, John Robertson reported (paper A13.1) that his group at Cambridge University has achieved n-channel mobility of 450 cm2/V-sec in microcrystalline silicon TFTs, and 100 cm2/V-sec p-channel mobility. Both those values are very good, and that's a problem. Plenty of models exist to explain why the material's mobility might be bad, and those models break when the mobility is good. More research needed.
(Special thanks to Dr. Robertson for walking me through yesterday morning's session on graphene, too.)
Meanwhile, Yifei Huang and a Princeton University group demonstrated (paper A13.2) a self-aligned process for low temperature polysilicon TFTs. It uses nickel silicide source and drain regions, aligned using the gate structure. At low annealing temperatures, the nickel doesn't react with the gate and can simply be etched away. Results were among the best ever recorded for top gate TFTs.
In the solar cell sessions, Makoto Shimosawa described (paper A14.1) Fuji Electric's FWave flexible solar material. It laminates roll-to-roll amorphous silicon/amorphous SiGe tandem cells (deposited by PECVD on plastic) onto steel foil. Each 2 square meter sheet generates 92 watts at peak output and weighs just 16 kg (including the steel foil). The company is now ramping production to wider rolls, targeting production of 40 MW per year.
The a-Si/a-SiGe tandem cell may be on its way out, though, as Xixiang Xu's group at United Solar Ovonic reported (paper A14.2) better results with small area triple junction a-Si/nanocrystalline-Si/nc-SI cells. Scale-up to large areas and optimization of the nc-Si component cell are the next steps.
The conference's own coverage is definitely worth a look as well.
Thursday, March 27, 2008
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