Metal oxide and semiconductor device

A semiconductor device comprising:

• a metal oxide comprising a channel formation region, a pair of electrodes in contact with the metal oxide, an insulator in contact with the metal oxide, and a gate electrode overlapping with the channel formation region with the insulator therebetween,
• wherein the metal oxide is a composite material which comprises:
• a plurality of first regions formed of a first material;
• and
• a second region formed of a second material,
• wherein the first material and the second material each comprise In, Zn and O,
• wherein the first material comprises Ga,
• wherein a concentration of In in the second material is higher than a concentration of In in the first material,
• wherein the first regions are irregularly dispersed in the second region,
• wherein each of the plurality of first regions has a size of greater than or equal to 0.5 nm and less than or equal to 2 nm,
• wherein an energy level of a conduction band minimum of the second material is lower than an energy level of the conduction band minimum of the first material by 0.2 eV or more,
• wherein an energy gap of first material is greater than or equal to 3.3 eV and less than or equal to 4.0 eV, and
• wherein an energy gap of the second material is greater than or equal to 2.2 eV and less than or equal to 2.9 eV.