First-principles study of native point defects in crystalline indium gallium zinc oxide

摘要

Materials in In-Ga-Zn-O system are promising candidates for channel layers of high-performance thin-film transistors (TFTs). We investigated the atomic arrangements and the electronic structures of crystalline InGaZnO_4 containing point defects such as oxygen vacancy (V_O), interstitial hydrogen (H_i), and interstitial oxygen (O_i) by density functional theory (DFT) using a plane-wave pseudopotential method. The calculations for the atomic structure relaxation suggest that H_i bonds to a lattice oxygen (O_o), and O_i occupies a split interstitial site [O_i(split)] forming a chemical bond with O_o which is similar to O_2 molecule, or O_i occupies an octahedral interstitial site [O_i(oct)]. The electronic structure calculations reveal that V_o forms fully occupied states around the middle of the DFT band gap, while H_i does not form a defect level in the band gap but raises the Fermi level above the conduction band minimum. O_i(split) forms fully occupied states above the valence band maximum of the rndefect-free model (VBM_0), while O_i(oct) forms both occupied and unoccupied states above the VBM_0. It is thus suggested that V_o and O_i(split) are electrically inactive for electrons but work as hole traps, H_i acts as a donor, and O_i(oct) is electrically active, trapping both electrons and holes. These observations imply that V_o and O_i(split) do not but H_i and O_i(oct) influence electrical properties of the n-channel TFTs based on the In-Ga-Zn-O semiconductor materials.