Electrical analysis of high-mobility poly-Si TFTs made from laser-irradiated sputtered Si Films

Polysilicon thin-film transistors (TFTs) fabricated from laser-irradiated sputtered Si films are electrically analyzed for carrier trap state density N/sub st/, temperature dependence of drain current, Hall effect, and potential profile in the channel. The field-effect mobility of the poly-Si TFTs increases 390 cm/sup 2//V-s with decreasing N/sub st/. With N/sub st/ decreasing, the activation energy obtained from the temperature dependence of drain current changes from a positive to a negative value which is almost equal to the value for single-crystal MOSFETs. Carrier velocity increases as N/sub st/ is decreased, but carrier concentration is nearly independent of N/sub st/. Plateau regions of zero electric field were observed in poly-Si TFTs with high N/sub st/. Therefore, it is concluded that high mobility occurs as a result of increasing carrier velocity, and electric field and of lowering the potential barrier by reducing N/sub st/.>