Amorphous In-Ga-Mg-O Thin Films Formed by RF Magnetron Sputtering: Optical, Electrical Properties and Thin-Film-Transistor Characteristics

We report on optical and electrical properties of amorphous In-Ga-Mg-O (a-IGMO) films and characteristics of a-IGMO channel thin-film transistors which went through the reductive post-annealing process. Optical band-gap energies of a-IGMO films were larger than that of amorphous In-Ga-Zn-O (a-IGZO) films. Carrier density and Hall mobility of a-IGMO films with the reductive post-annealing were almost the same degree as those of a-IGZO films. Although the reductive annealing with the SiN _x underlayer makes an a-IGZO film degenerate semiconductor and its TFT inoperative, a-IGMO TFTs successfully operated after this reductive process. Break-junction tunnelling spectroscopy which was applicable not to a-IGMO but to a-IGZO with the reductive process showed a noticeable density of state character in the vicinity of the Fermi level for a-IGZO, which is consistent with its property.