Point defects and electrical properties of Sn-doped In-based transparent conducting oxides (original) (raw)
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Modeling the structural properties and energies of transparent conducting oxides
Thin Solid Films, 2007
In the current study we evaluate the use of a dumped shifted force electrostatic interaction model for the study of the structural properties of indium oxide and tin-doped indium oxide (ITO). This model is found to be computationally efficient and accurate in the calculations. More specifically, the ion positions of In 2 O 3 , the preference of b-sites In substitution with Sn and the lattice constant of ITO anomalous dependency on Sn content varying from 3% to 6% calculated with this model agree with the experimental data and other theoretical first principle studies. For Sn content higher than 6% the calculated data deviate from the experimentally observed as the existence of the In 4 Sn 3 O 12 phase was not taken into account. Also, we found an agreement to the Vegard's law of the lattice constant with simple In substitution with Sn ions. Finally the bulk modulus calculated for the ITO (92-97 GPa) is in good agreement with experimental data for ITO films.
Materials
Low-temperature-processed ITO thin films offer the potential of overcoming the doping limit by suppressing the equilibrium of compensating oxygen interstitial defects. To elucidate this potential, electrical properties of Sn-doped In 2 O 3 (ITO) thin films are studied in dependence on film thickness. In-operando conductivity and Hall effect measurements during annealing of room-temperature-deposited films, together with different film thickness in different environments, allow to discriminate between the effects of crystallization, grain growth, donor activation and oxygen diffusion on carrier concentrations and mobilities. At 200 ∘ C , a control of carrier concentration by oxygen incorporation or extraction is only dominant for very thin films. The electrical properties of thicker films deposited at room temperature are mostly affected by the grain size. The remaining diffusivity of compensating oxygen defects at 200 ∘ C is sufficient to screen the high Fermi level induced by depos...
materials Transparent Conducting Oxides—An Up-To-Date Overview
Transparent conducting oxides (TCOs) are electrical conductive materials with comparably low absorption of electromagnetic waves within the visible region of the spectrum. They are usually prepared with thin film technologies and used in opto-electrical apparatus such as solar cells, displays, opto-electrical interfaces and circuitries. Here, based on a modern database-system, aspects of up-to-date material selections and applications for transparent conducting oxides are sketched, and references for detailed information are given. As n-type TCOs are of special importance for thin film solar cell production, indium-tin oxide (ITO) and the reasonably priced aluminum-doped zinc oxide (ZnO:Al), are discussed with view on preparation, characterization and special occurrences. For completion, the recently frequently mentioned typical p-type delafossite TCOs are described as well, providing a variety of references, as a detailed discussion is not reasonable within an overview publication.
Journal of Alloys and Compounds, 2018
At substrate temperature (T S) close to melting point of Sn (T Sn) rapid incorporation of metallic dopants in significant amount introduces sharp rise in mobility (m) and concentration (n e) of charge carriers, leading to substantial reduction in resistivity (r); simultaneous sharp widening in optical gap (E g) results in optimum Figure-of-Merit (F). The E g vs. n e 2/3 plot demonstrates two distinct regimes of T S across T Sn , leading to higher reduced effective mass of charge carriers, m * vc by 0.072m 0 owing to rapid incorporation of Sn 4þ at substitutional site of In 3þ in In 2 O 3 matrix. Consequently, the self-energy due to electronimpurity scattering rises and/or the material self-converts to an alloy-like ensemble. On further increase in T S , F reduces due to enhanced optical absorption by metallic dopants and dopant induced defects, as noted by enhanced Urbach-energy (E U). Rather than any arbitrary T S , T Sn has been demonstrated as an optimal growth temperature for ITO films grown by RF magnetron sputtering.
Surface studies of crystalline and amorphous Zn–In–Sn–O transparent conducting oxides
Thin Solid Films, 2012
X-ray and ultraviolet photoelectron spectroscopy (UPS) studies were made of in situ RF magnetron-sputtered crystalline (c) and amorphous (a) Zn-In-Sn-O (ZITO) thin films, ex situ pulsed laser deposited c-and a-ZITO thin films, and bulk ZITO ceramics. Cosubstitution of Zn and Sn for In results in an increase of the In core level binding energy at a given Fermi level compared to that measured in undoped and Sn-doped In 2 O 3 (ITO). In plots of work function vs. Fermi level, in situ c-ZITO and a-ZITO films have low ionization potentials (7.0-7.7 eV) that are similar to undoped In 2 O 3. In contrast, dry-air-annealed in situ films, ex situ films, and bulk ceramics have higher ionization potentials (7.7-8.1 eV) that are more similar to ITO and match well with previous work on air-exposed surfaces. Kelvin Probe measurements were made of select a-ZITO films exposed to air and ultraviolet/ozone-treated so as to measure work functions under conditions commonly employed for device fabrication. Results (4.8-5.3 eV) were in good agreement with the UPS work functions of oxygen-exposed materials and with literature values. Lastly, a parallelogram plot of work function vs. Fermi level shows that a wider range of work functions is achievable in ZITO materials as compared to other transparent conducting oxides (Sb-doped SnO 2 , Al-doped ZnO, Sn-doped In 2 O 3), making ZITO more versatile for applications.
Solid State Sciences, 2012
Indium oxide co-doped with tin and zinc (ITZO) ceramics have been successfully prepared by direct sintering of the powders mixture at 1300 C. This allowed us to easily fabricate large highly dense target suitable for sputtering transparent conducting oxide (TCO) films, without using any cold or hot pressing techniques. Hence, the optimized ITZO ceramic reaches a high relative bulk density (w 92% of In 2 O 3 theoretical density) and higher than the well-known indium oxide doped with tin (ITO) prepared under similar conditions. All X-ray diagrams obtained for ITZO ceramics confirms a bixbyte structure typical for In 2 O 3 only. This indicates a higher solubility limit of Sn and Zn when they are co-doped into In 2 O 3 forming a solid-solution. A very low value of electrical resistivity is obtained for [In 2 O 3 :Sn 0.10 ]:Zn 0.10 (1.7 Â 10 À3 U cm, lower than ITO counterpart) which could be fabricated to high dense ceramic target suing pressure-less sintering.
Physical Review B, 2010
The electronic properties of single- and multication transparent conducting oxides (TCOs) are investigated using first-principles density-functional approach. A detailed comparison of the electronic band structure of stoichiometric and oxygen deficient In2O3 , α , and β-Ga2O3 , rock salt and wurtzite ZnO, and layered InGaZnO4 reveals the role of the following factors which govern the transport and optical properties of these TCO materials: (i) the crystal symmetry of the oxides, including both the oxygen coordination and the long-range structural anisotropy; (ii) the electronic configuration of the cation(s), specifically, the type of orbital(s)— s , p , or d —which form the conduction band; and (iii) the strength of the hybridization between the cation’s states and the p states of the neighboring oxygen atoms. The results not only explain the experimentally observed trends in the electrical conductivity in the single-cation TCO, but also demonstrate that multicomponent oxides may offer a way to overcome the electron localization bottleneck which limits the charge transport in wide band-gap main-group metal oxides. Further, the advantages of aliovalent substitutional doping—an alternative route to generate carriers in a TCO host—are outlined based on the electronic band structure calculations of Sn, Ga, Ti, and Zr-doped InGaZnO4 . We show that the transition metal dopants offer a possibility to improve conductivity without compromising the optical transmittance.
A novel transparent pn+ junction based on indium tin oxides
Thin Solid Films, 2004
p-Type indium-doped SnO thin films were successfully fabricated on degenerate n indium tin oxide glass and quartz glass q 2 by sol gel dip-coating method. It was found from the X-ray diffraction results that indium-doped SnO thin films were in the 2 same rutile structure as that of undoped SnO . Hall effect measurement results showed that for InySn ratioF0.33 and process 2 temperature approximately 525 8C, the indium-doped tin oxide were p-type. The I-V curve measurement of a prototype transparent pn junction consisting of a layer of p-type indium-doped SnO and a layer of degenerate n tin-doped indium oxide showed q q 2 typical rectifying characteristics. ᮊ