| Autor: |
Choi, W.K., Cho, J.S., Song, S.K., Jung, H.-J., Koh, S.K., Yoon, K.H., Lee, C.M., Sung, M.C., Jeong, K. |
| Zdroj: |
Thin Solid Films; July 1997, Vol. 304 Issue: 1-2 p85-97, 13p |
| Abstrakt: |
Undoped oxygen-deficient SnOx films were deposited on Si (100) and BK7 glass substrates by the reactive ion-assisted deposition technique. The average impinging energy (Ea) of the oxygen ion on depositing a Sn atom, a relative arrival ratio of ion to atom (Γ), was varied from Γ = 0.025 (Ea = 25 eV atom−1) to Γ = 0.1 (Ea = 100 eV atom−1) by controlling the discharge voltage at a fixed ion-beam potential of 500 V. Crystalline structures of as-deposited SnOx films appeared to be amorphous for all Ea values. In order to precisely examine the dependence of oxidation from SnO to SnO2 on initial oxygen content and annealing temperature, as-deposited SnOx films containing initially different oxygen contents were annealed at 400 ∼ 500 °C in a low vacuum (∼5 × 10−3 Torr) for 1 h to remove the external oxygen diffusion effect during the annealing process. The heat-treated SnOx films at 400 °C showed polycrystalline SnO structure until Ea = 50 eV atom−1 and were still amorphous over Ea = 75 eV atom−1. But after annealing over 500 °C those films over Ea = 75 eV atom−1 exhibited diffraction peaks at (110), (101), and (211), characteristic of polycrystalline SnO2. Scanning electron microscopy (SEM) micrographs for the as-deposited SnOx films show grains as small as a few tens of ångstroms in size, but those after 500 °C annealing reveals that the number of granular grain became larger in cross-sectional SEM and the grain grew to 300 Å at Ea = 100 eV atom−1. For as-deposited films, the root-mean-square of surface roughness (σ) slightly increased from 9 to 25 Å as Ea was increased, but conversely it reduced from 36 Å to 13 Å after annealing. From quantitative Auger electron spectroscopy, it was observed that characteristic transitional Auger peaks of Sn MNN shift to lower kinetic energy by as much as 3.8 ∼ 4.2 ± 0.02 eV in the case of the SnO films and 4.8 ∼ 5.2 ± 0.02 eV for SnO2 films, respectively, with respect to that of Sn metal (Sn0). Based on the valence band spectra taken by using He I angle-resolved ultraviolet photoelectron spectroscopy (angle-resolved UPS), two different phases of polycrystalline SnO and SnO2 films were clearly distinguished. The binding energy difference between the first peaks derived from SnO and SnO2 films in angle-resolved UPS spectra below the Fermi level was 1.6 eV. This value is very close to the value obtained from clean SnO and SnO2 samples by previous valence-band XPS spectra. As-deposited and annealed films showed optical transmittance as high as more than 80% grown at higher than Ea = 50 eV atom−1 in the visible wavelength and refractive index close to the bulk SnO2 value for the film deposited at Ea = 100 eV atom−1 after annealing. |
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