연 X-선 분광법을 이용한 a-GIZO 박막의 분광학적 특성 연구

Abstract

Amorphous gallium indium zinc oxide (a-GIZO) thin films of different compositions (Ga2O3: In2O3: ZnO = 1:1:1, 2:2:1, 3:2:1, 4:2:1) on Si substrate were investigated by high-resolution x-ray photoelectron spectroscopy (XPS) and x-ray absorption spectroscopy (XAS) using synchrotron radiation. The O 1s, Ga 3d, In 4d, Zn 3d core and shallow-core levels as well as the valence band maxima and the O K-edge XAS were investigated. Each O 1s spectrum could be deconvoluted by a main component (O1 component in the text) representing Ga-In-Zn-O quarternary system along with two other higher-binding energy components (O2 and O3 in the text). The O3 intensity increased as the Ga2O3 content increased. The spectral peak separations between the Ga 3d (~20 eV) and Zn 3d (~12 eV) orbitals and between the In 4d (~19 eV) and Zn 3d orbitals became larger, respectively, as Ga2O3 content increased. The valence band maximum shifted towards higher binding energy (BE), upto ~0.5 eV for the as-prepared samples and ~0.25 eV for the cleaned samples, and the conduction band minimum (measured at the O K-edge) was measured at photon energies ranging upwards to ~0.2eV as the Ga2O3 content increased, demonstrating that the band gap can be tailored by increasing the Ga2O3 content. Finally, the effects on the local chemical states and the corresponding electrical conduction by increasing the Ga2O3 content are discussed.Then, the Ne+ ion sputtering effect on amorphous-Ga-In-Zn-O (a-GIZO) thin-film was investigated in an attempt to understand the conductance increase of the film by sputtering. The O 1s, Ga 3d, In 4d, Zn 3d, valence band, and O K-edge spectral analysis showed that the sputtering reduced Zn and In contents relative to that of Ga, resulting in more oxidized environment for Ga and In atoms, and also generated an subgap state in the valence band. Further sputtering resulted in metallic In, the more for the lower Zn and In content film. The generation of subgap state and metallic In is suggested to be a cause of effective increase of conductance by sputtering.