We have developed a state-of-the-art technology to tailor oxygen-related point defects such as oxygen vacancies (V O ) and structural defects of polycrystalline highly conductive Sn-doped In 2 O 3 (ITO) films by a postirradiation of electronegative oxygen (O − ) ions. The intentional oxygen doping that would annihilate V O decreases carrier density (n e ) from 9.3 × 10 20 to 7.1 × 10 20 cm −3 with an increase of Hall mobility (μ H ) from 44 to 51 cm 2 •V −1 •s −1 , and subsequently, n e drastically decreases down to 1.2 × 10 19 cm −3 together with a decrease in μ H owing to a formation of Sn−O neutral complexes with a further increase in the amount of oxygen atoms that should fill the structural defects while retaining their crystal structure. Upon the filling of the structural vacancies, the successful control of intrinsic point defects is probably caused by almost no difference in the ionic radii between In 3+ having six-coordination and Sn 4+ having eight-coordination. The O − -ion-irradiation technology enables one to tailor the physical properties of ITO films over a wide range while retaining the crystal structure of the films.

We demonstrated that a mass density and size effect are dominant factors to limit the transport properties of very thin amorphous Sn-doped In 2 O 3 ( a -ITO) films. a -ITO films with various thicknesses ( t ) ranging from 5 to 50 nm were deposited on non-alkali glass substrates without intentional heating of the substrates by reactive plasma deposition with direct-current arc discharge. a -ITO films with t of more than 10 nm showed a high Hall mobility ( μ H ) of more than 50 cm 2 /V s. For 5-nm-thick a -ITO films, we found that μ H was as high as more than 40 cm 2 /V s. X-ray reflectivity measurement results revealed that the mass density ( d m ) determined the carrier transport in a -ITO films. For a -ITO films with t of more than 10 nm, d m had a high value of 7.2 g/cm 3 , whereas a -ITO films with t of less than 10 nm had low d m ranging from 6.6 to 6.8 g/cm 3 . Quantitative new insight from a size effect on the carrier transport is given for a -ITO films with t of less than 10 nm. This study shows that the ratio of t to mean free path of carrier electrons governed μ H .

We elucidated implicate ordering of amorphous Sn-doped In2O3 films grown on glass substrates during the phase transition to polycrystalline by postannealing from room temperature to 300 °C for 55 min. X-ray diffraction with two-dimensional detector revealed the following. First, fine grains are developed. Second, crystallites are grown with (222) preferential orientation associated with growing crystallites along (222) plane. Simultaneously, the alignment between grains is also promoted. Finally, while retaining the alignments among crystallites, long-range ordering was improved within the crystallites. Based on those findings, as a well-defined crystallization temperature, we propose a temperature at which the above-mentioned final stage starts.

We demonstrate that the state-of-the-art postirradiation technology for negatively charged oxygen (O−) ions is effective for tailoring carrier concentration (n e ), electrical resistivity (ρ), and optical band gap (E g) in a wide range for polycrystalline 50-nm-thick Sn-doped In2O3 (ITO) films on glass substrates by reactive plasma deposition with direct-current arc discharge. As-deposited ITO films showed n e of 9.2 × 1020 cm−3, ρ of 1.5 × 10−4 Ω cm, and E g of 3.50 eV. The postirradiation of O− ions for 180 min at 250 °C decreased n e to 2.4 × 1018 cm−3. This resulted in a significant increase in ρ to 3.5 × 10−1 Ω cm while retaining the bixbyite crystal structure and the spatial distribution of Sn dopant atoms. The postirradiation of O− ions led to the continuous decrease in the optical E g ranging from 3.50 to 3.02 eV, which is smaller than that of undoped In2O3. For degenerate ITO films, conventional theories about the broadening and narrowing of the optical E g explain the experimental results well. On the other hand, for nondegenerate ITO films, the optical E g shrinkage would be mainly caused by an upward energy shift attributable to the generation of the anti-bonding π* states between O 2p and In 4d orbitals within the topmost valence band owing to the lattice disorder associated with incorporated interstitial oxygen atoms that fill structural vacancy sites. On the basis of the Ioffe–Regel criterion utilizing the electron mean free path, Fermi momentum, and their product, we determined the critical n e at which degenerate ITO films transform to nondegenerate ones.

Metrics & MoreArticle Recommendations D ue to an arrangement mistake of X-ray diffraction (XRD) equipment, we detected a strong peak at 2θ ≈ 44.27°. For the calculations of lattice constants of as-deposited and O − -ionirradiated Sn-doped In 2 O 3 (ITO) films, as a result, we overestimated lattice parameters, as described below, by approximately 0.82% in the published manuscript.We measured XRD profiles for all the ITO films with a proper arrangement. The corrected data are shown in Figure 3. Figure 3a shows strong ( 222) and ( 440) peaks with very weak ( 431) and ( 622) peaks, regardless of O − -ion irradiation time t irr . As shown in Figure 3b, the lattice parameter of the as-deposited ITO film was a = 1.0184 nm. The O − -ion irradiation resulted in a decrease in the lattice parameters monotonically down to 1.0171 nm. The variation of the lattice parameters was found to be as small as 0.12% over the entire range of t irr . As shown in Figure 3c, the intensity ratios of I(440)/I(222) remain almost constant during the O − -ion irradiation. Figure 3d shows that Δ2θ(222) at t irr of 30 min was increased by 9.9% compared with that of asdeposited ITO films. The values of Δ2θ(222) obtained by the Lorentzian function approach used in the published article were underestimated: in this work, we found that a Gaussian function fitting approach for the data in Figure 3d is more suitable for reproducing peak shapes compared with those obtained by a Lorentzian function used in the published article. These changes do not affect the rest of the conclusions in the published article.