| AVS 56th International Symposium & Exhibition | |
| Thin Film | Thursday Sessions |
| Session TF-ThP |
| Session: | Aspects of Thin Films Poster Session |
| Presenter: | A. Takasaki, Aoyama Gakuin University, Japan |
| Authors: | A. Takasaki, Aoyama Gakuin University, Japan Y. Sato, Aoyama Gakuin University, Japan N. Oka, Aoyama Gakuin University, Japan F. Utsuno, Idemitsu Kosan Co., Ltd., Japan K. Yano, Idemitsu Kosan Co., Ltd., Japan Y. Shigesato, Aoyama Gakuin University, Japan |
| Correspondent: | Click to Email |
Sn-doped In2O3 (ITO) film has been used as a transparent electrode for various applications including organic light-emitting diodes (OLEDs) since it combines good conductivity and transparency in the visible region. The work function control of ITO film plays an important role in device parameters such as operation voltage or lifetime for OLED. The work function of ITO film has been controlled by surface treatments by plasma or UV-ozone treatment. However in such methods the work function of ITO film is unstable and can change over time. On the other hand, it is expected that the work function could be controlled by a variation in carrier density. In this study, we investigate how the work function depends on the carrier density of ITO films. The ITO films with various carrier densities were deposited by dc magnetron sputtering on glass substrates heated at 300 oC and 400 oC using high-density ceramic ITO targets with various SnO2 concentrations. Total gas pressure and dc power were maintained at 1.0 Pa and 50 W, respectively, for all the depositions. The film thickness of all the ITO films was adjusted as about 200 nm. Carrier density was controlled from 3.06 ×1019‐5.72×1020 cm-3 or 4.42 ×1019‐1.08×1021 cm-3 for the films deposited on the substrates heated at 300 oC or 400 oC, respectively, by using the ceramic ITO targets with the different SnO2 concentrations from 0 to 10 wt. %. The increase in the carrier density should be caused by the increase in the substitutional Sn4+ at In3+ sites of In2O3. Optical band gap of the films increased with the increasing SnO2 concentration of the target, where work function decreased. This must be explained quantitatively in terms of the shift of Fermi level with varying carrier density within a parabolic conduction band. The optical band gap or the work function of the films showed clearly positive or negative relationships to the two-thirds power of carrier density, respectively. Furthermore, a detailed analysis was performed using hard X-ray photoemission spectroscopy (HX-PES) in order to investigate the electronic state between the Fermi level and the valence band of ITO films deposited on the substrates heated at 400 oC. As a result, the density of state near the Fermi level was found to vary systematically with the carrier density. The synchrotron radiation experiments were performed at the BL47XU in the SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute (JASRI) (Proposal No.2009A1586).