Semiconductor Device and Method for Evaluating Semiconductor Device

A semiconductor device comprising:

• a transistor including an oxide semiconductor layer in a channel formation region, the oxide semiconductor layer being electrically connected to a first electrode and a second electrode,
• wherein, while a voltage is applied between the first electrode and the second electrode, the oxide semiconductor layer begins to be irradiated with light having a peak intensity in a wavelength range of 340 nm to 360 nm and an intensity of 3 mW/cm2 at a temperature of 25° C. at a time T0 and irradiation is stopped at a time T1,
• wherein a value of a current flowing between the first electrode and the second electrode at a time T2 is greater than or equal to 70% and less than 100% of a maximum value of a current flowing between the first electrode and the second electrode between the time T0 and the time T1,
• wherein a value of a current flowing between the first electrode and the second electrode at a time T3 is greater than or equal to 5% and less than 100% of the maximum value of the current flowing between the first electrode and the second electrode between the time T0 and the time T1,
• wherein the time T2 is after a period of greater than or equal to 1 second and less than or equal to 15 seconds from the time T0 and before the time T1, and
• wherein the time T3 is after a period of greater than or equal to 1 second and less than or equal to 15 seconds from the time T1.

An evaluation method for a semiconductor device comprising the steps of:

• starting to apply a voltage between a first electrode and a second electrode at a time T0 so that a current flows in an oxide semiconductor layer electrically connected to the first electrode and the second electrode;
• irradiating the oxide semiconductor layer with light having an energy higher than an energy gap of the oxide semiconductor layer, wherein the irradiating step starts at a time T1 and stops at a time T2;
• comparing a value of a current flowing between the first electrode and the second electrode at a time T3 with a maximum value of a current flowing between the first electrode and the second electrode between the time T1 and the time T2;
• and
• comparing a value of a current flowing between the first electrode and the second electrode at a time T4 with the maximum value of the current flowing between the first electrode and the second electrode between the time T1 and the time T2;
• and
• stopping to apply the voltage between the first electrode and the second at time T5,
• wherein the time T1 is after the time T0,
• wherein the time T3 is between the time T1 and the time T2,
• wherein the time T4 is after a period of greater than or equal to 1 second and less than or equal to 15 seconds from the time T2, and
• wherein the time T5 is after the time T4.