ELECTRICAL ANALYSIS OF HIGH-MOBILITY POLY-SI TFTS MADE FROM LASER-IRRADIATED SPUTTERED SI FILMS

Poly-Si TFT's are fabricated from laser-irradiated sputtered Si films. The poly-Si TFT's are electrically analyzed for carrier trap state density N(st), temperature dependence of drain current, Hall effect, and potential profile in the channel. Field-effect mobility of the poly-Si TFT's increases 390 cm2/V . s with decreasing of N(st). Also, with N(st) decreasing, the activation energy obtained from temperature dependence of drain current changes from positive to negative value, which is almost equal to the value for single-crystal MOSFET's. It is found that carrier velocity increases as carrier trap state density N(st) is decreased, but that carrier concentration is nearly independent of N(st). Moreover, plateau regions of zero electric field are observed in poly-Si TFT's with high N(st). Therefore, it is concluded that high mobility occurs as results of increasing carrier velocity and electric field, and of lowering the potential barrier by reducing N(st).