Amorphous In-Ga-Zn-O was expected for channel layers in thin-film transistors. It was known that amorphous In-Ga-Zn-O was sensitive to an O/H-containing atmosphere; therefore, it was important to clarify the roles of oxygen and hydrogen in amorphous In-Ga-Zn-O. The present work presented atomic and electronic structures, defect formation energies and bond energies in amorphous In-Ga-Zn-O calculated by first-principles density functional theory. It was confirmed that oxygen deficiencies having low formation energies (2 to 3.6 eV) formed either deep fully-occupied localized states near the valence band maximum or donor states, which depended on their local structures. All the hydrogen doping formed -OH bonds and worked as a donor. The stable -OH bonds had a small formation energy of ∼0.45eV and consisted of three metal cations coordinated to the O ion. The bond energy of Ga-O was calculated to be ∼2.0 eV, which was the largest among the chemical bonds in amorphous In-Ga-Zn-O (1.7eV for In-O and 1.5eV for ZnO). This result supported the idea that the incorporation of Ga stabilized amorphous In-Ga-Zn-O thin-film transistors.

Sub-Gap States, Doping and Defect Formation Energies in Amorphous Oxide Semiconductor a-InGaZnO4 Studied by Density Functional Theory. T.Kamiya, K.Nomura, H.Hosono: Physica Status Solidi A, 2010, 207[7], 1698–703