Patent ID: 8168974

Claim:
A field-effect transistor provided with a source electrode, a drain electrode, a gate insulator, a gate electrode, and a transparent channel layer, wherein the channel layer comprises an amorphous oxide of a compound having (a) a composition when in crystalline state represented by In 2-x M3 x O 3 (Zn 1-y M2 y O) m , wherein M2 is Mg or Ca; M3 is B, Al, Ga or Y; 0≦x≦2; 0≦y≦1; and m is zero or a natural number less than 6, or a mixture of said compounds; (b) an electron carrier concentration of 10 12 /cm 3 or more and less than 10 18 /cm 3 , wherein an electron mobility of the channel layer tends to increase with increase of the electron carrier concentration; and (c) an oxygen defect density decreased by treatment in an atmosphere containing oxygen at a predetermined pressure during or after formation of the amorphous oxide; and at least one of the source electrode, the drain electrode and the gate electrode is transparent to visible light, wherein current between the drain electrode and the source electrode when no gate voltage is applied is less than 10 microamperes.