Semiconductor device

A semiconductor device comprising:

• a gate electrode;
• a gate insulating film over the gate electrode;
• a multilayer film over the gate insulating film, the multilayer film comprising an oxide layer and an oxide semiconductor layer;
• a source electrode in contact with a top surface of the oxide layer;
• and
• a drain electrode in contact with the top surface of the oxide layer,
• wherein the oxide layer comprises indium and a metal element,
• wherein the oxide semiconductor layer comprises indium and the metal element, and
• wherein an absorption coefficient of the multilayer film measured from a constant photocurrent method is lower than 1×10−3 cm−1.

A semiconductor device comprising:

• a gate electrode;
• a gate insulating film over the gate electrode;
• a multilayer film over the gate insulating film, the multilayer film comprising an oxide layer and an oxide semiconductor layer;
• a source electrode in contact with a top surface of the oxide layer;
• and
• a drain electrode in contact with the top surface of the oxide layer,
• wherein the oxide layer comprises indium and a metal element,
• wherein the oxide semiconductor layer comprises indium and the metal element,
• wherein a mixed layer is formed in the multilayer film by moving oxygen between the oxide layer and the oxide semiconductor layer,
• wherein an atomic ratio of the metal element to indium of the oxide layer is 1.5 times or more as large as an atomic ratio of the metal element to indium of the oxide semiconductor layer,
• wherein an atomic ratio of the metal element to indium of the mixed layer is larger than the atomic ratio of the metal element to indium of the oxide semiconductor layer,
• wherein the atomic ratio of the metal element to indium of the mixed layer is smaller than the atomic ratio of the metal element to indium of the oxide layer, and
• wherein an absorption coefficient of the multilayer film measured from a constant photocurrent method is lower than 1×10−3 cm−1.