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_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 ²/V-s with decreasing N_st. With N_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_st is decreased, but carrier concentration is nearly independent of N _st. Plateau regions of zero electric field were observed in poly-Si TFTs with high N_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_st