| abstract |
An oxide semiconductor layer in which “safe” traps exist exhibits two kinds of modes in photoresponse characteristics. By using the oxide semiconductor layer, a transistor in which light deterioration is suppressed to the minimum and the electric characteristics are stable can be achieved. The oxide semiconductor layer exhibiting two kinds of modes in photoresponse characteristics has a photoelectric current value of 1 pA to 10 nA inclusive. When the average time τ 1 until which carriers are captured by the “safe” traps is large enough, there are two kinds of modes in photoresponse characteristics, that is, a region where the current value falls rapidly and a region where the current value falls gradually, in the result of a change in photoelectric current over time. |