We investigate the evolution behavior of defect structures and the subgap states in In-Ga-Zn oxide (IGZO) films with increasing postannealing temperature by means of extended x-ray absorption fine-structure (EXAFS) measurements, positron annihilation lifetime spectroscopy (PALS), and cathodoluminescence (CL) spectroscopy, aiming to understand the relationship between defect structures and subgap states. EXAFS measurements reveal the varied oxygen coordination numbers around cations during postannealing and confirm two types of point defects, namely, excess oxygen around Ga atoms and oxygen deficiency around In and/or Zn atoms. PALS suggests the existence of cation-vacancy (VM)-related clusters with neutral or negative charge in both amorphous and polycrystalline IGZO films. CL spectra show a main emission band at approximately 1.85 eV for IGZO films, and a distinct shoulder located at about 2.15 eV for IGZO films postannealed above 600 °C. These two emission bands are assigned to a recombination between the electrons in the conduction band and/or in the shallow donor levels near the conduction band and the acceptors trapped above the valence-band maximum. The shallow donors are attributed to the oxygen deficiency, and the acceptors are thought to possibly arise from the excess oxygen or the VM-related clusters. These results open up an alternative route for understanding the device instability of amorphous IGZO-based thin-film transistors, especially the presence of the neutral or negatively charged VM-related clusters in amorphous IGZO films.

The origin of negative ions in the dc magnetron sputtering process using a ceramic indium-gallium-zinc oxide target has been investigated by in situ analyses. The observed negative ions are mainly O- with energies corresponding to the target voltage, which originates from the target and barely from the reactive gas (O2). Dissociation of ZnO-, GaO-, ZnO2 -, and GaO2 - radicals also contributes to the total negative ion flux. Furthermore, we find that some sputtering parameters, such as the type of sputtering gas (Ar or Kr), sputtering power, total gas pressure, and magnetic field strength at the target surface, can be used to control the energy distribution of the O- ion flux. © 2013 AIP Publishing LLC.

The shift of the Fermi level in polycrystalline aluminum doped zinc oxide (AZO) films was studied by investigating the carrier density dependence of the optical band gap and work function. The optical band gap showed a positive linear relationship with the two-thirds power of carrier density n(e)(2/3). The work function ranged from 4.56 to 4.73 eV and showed a negative linear relationship with n(e)(2/3). These two phenomena are well explained on the basis of Burstein-Moss effect by considering the nonparabolic nature of the conduction band, indicating that the shift of Fermi level exhibits a nonparabolic nature of the conduction band for the polycrystalline AZO film. The variation of work function with the carrier density reveals that the shift of the surface Fermi level can be tailored by the carrier density in the polycrystalline AZO films. The controllability between the work function and the carrier density in polycrystalline AZO films offers great potential advantages in the development of optoelectronic devices. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4733969]

The performance of a semiconductor device crucially depends on the carrier concentration of the semiconducting material. The hole concentration is governed by the density of states (DOS) and the Fermi–Dirac distribution, indicating the importance of the DOS in the top region of the valence band. Herein, the DOS of the valence band top region of nondoped and nitrogen‐doped Cu₂O films using UV photoelectron spectroscopy and constant‐final‐state yield spectroscopy is measured. The obtained DOS varies over six orders of magnitude from the valence band to the Fermi level. Judging from the DOS and the hole density observed from the Hall effect measurements, the valence band maximum (VBM) in the DOS distribution is then determined. The traditional method of determining the VBM by linear extrapolation of the onset region cannot reproduce the hole density; instead, the calculation requires the weak DOS of the in‐gap states above the traditional VBM up to the Fermi level. The wave function difference between the valence states and in‐gap states, observed using constant‐initial‐state yield spectroscopy, suggests that the traditional VBM is close to the border at which the wave function switches from conducting valence states to trap‐like in‐gap states.

Abstract

To investigate the thermal-switching properties of Pd-catalyzed Ni-Mg alloy films, we conducted in-situ analyses of the films’ electrical, optical, and thermal properties through hydrogen gasochromic reactions. These reactions allow the films to reversibly switch between metallic (dehydride) and semiconductor (hydride) phases. The thermal conductivities of the metallic and semiconductor states were found to be 14 and 1.0 Wm−1K−1, respectively. By applying the Wiedemann–Franz law (WFL), we attributed the significant decrease in thermal conductivity during hydrogenation to the reduction in free electrons.

The ultrafast transient behavior of InN under intensive laser irradiation remains unclear. The simultaneous measurements of pump–probe transient transmission and reflectivity are reported in this study. The irradiation-induced change in the dielectric constant of InN films due to the generation of thermalized carriers gives rise to complex transient behavior, and simultaneous increase in both transient transmission and reflectivity are observed at certain wavelengths. Herein, transient transmission is interpreted as the occupation probability of thermalized electrons at the probing level originating from a hot Fermi–Dirac distribution, and our calculation results are in good agreement with the experiments. Likewise, the Drude-like response due to the collective motion of thermalized carriers causes the increase in transient reflectivity, which depends on the change of dielectric constant caused by the collective motion of thermalized carriers. The ultrafast carrier dynamics is modeled by calculating the temporal evolution of the occupation probability of thermalized electrons in the conduction band. On the basis of the two-temperature model, the electron–phonon scattering time is extrapolated to be [Formula: see text] fs in InN, which dominates the cooling of excited electrons.

MgSnN2 with an average wurtzite structure (wz-MgSnN2) has recently emerged as a pseudo-III-nitride semiconductor, studied for applications in tandem solar cells, green light-emitting diodes, and other optoelectronic devices. This compound has only been researched recently, and, therefore, its charge-carrier transport properties are poorly understood. Understanding these properties is essential for optoelectronic applications. In this study, we grew wz-Mg1-xSn1+xN2 biaxially oriented polycrystalline films with x = -0.08 to 0.29 by reactive sputtering and investigated the charge-carrier transport properties using both direct current and optical techniques. We regarded the wz-Mg1-xSn1+xN2 films as magnesium tin oxynitride films (wz-MTNO) because a certain amount of oxygen was unintentionally incorporated into the sputtered wz-Mg1-xSn1+xN2 films. The wz-MTNO layers were n-type degenerate semiconductors with an electron density (n(e)) of the order of 10(20) cm(-3). In films with n(e) > 8 x 10(20) cm(-3), optically extracted resistivities (rho(opt)) obtained via a Drude-fit analysis of the infrared transmittance and reflectance spectra were almost identical to the direct-current resistivities (rho(dc)), indicating that the contribution of grain boundary scattering to the electron transport was negligible. However, the contribution of grain boundary scattering became unignorable with decreasing n(e). The Drude-fit analysis also allowed the determination of the conduction-band effective mass (m(c)*) for the first time. A band edge mass of m(c)*/m(0) & AP; 0.2 (m(0) denotes the free-electron mass) was obtained in the wz-MTNO layers with |x| < 0.1. As x was increased from -0.18 to 0.29, m(c)*/m(0) substantially increased from 0.18 to 0.56, indicating that the conduction-band dispersion decreased. That is, the conduction-band dispersion may be affected by the cation composition x. The findings of this study will provide important information to establish this material as a practical nitride semiconductor.

Herein, wurtzite-type MgSnN2-ZnSnN2 alloys (MgxZn1-xSnN2) are proposed as earth-abundant and band gap-tunable semiconductors with fundamental band gaps in the range of 1.5-2.3 eV. The alloys do not exhibit immiscibility, unlike the InN-GaN system, because the lattice mismatch between the endmembers is smaller than 1% in both a- and c-axis directions. The MgxZn1-xSnN2 alloys can be epitaxially grown on GaN(001) in the whole x range, and their fundamental band gap can be tuned from 1.5 to 2.3 eV with the increase in x from 0 to 1. Moreover, the MgxZn1-xSnN2 epilayers with x > 0.53 exhibit a green-light photoluminescence emission near room temperature, which indicates that they are direct-gap semiconductors. Direct-gap semiconductors with band gaps of 1.8-2.5 eV are eagerly anticipated for the development of green light-emitting diodes (LEDs) and top cells in high-efficiency tandem solar cells, though such wurtzite- or zincblende-type compounds that can be epitaxially integrated with conventional semiconductors are quite rare. Therefore, MgxZn1-xSnN2 alloys are attractive nitride semiconductors toward the development of green-LEDs and tandem solar cells.

AlN thin piezoelectric films are attractive for RF filter applications because of their low mechanical loss 1/Q(m). We here introduce new AlN based materials: polarization inverted ScAlN multilayer and YbAlN films. Enhancement of electromechanical coupling coefficient in YbAlN were theoretically and experimentally demonstrated. These materials are promising for application in BAW and SAW devices.

© Copyright Materials Research Society 2018. The use of zinc nitride (Zn3N2) films as a transparent electrode in various electronic devices has attracted much attention owing to its high-carrier mobility. In this study, we investigate the influence of the sputtering process on structural, optical, and electrical properties of a Zn3N2 film deposited by reactive magnetron sputtering. The reactivity of nitrogen species can be improved by changing the type of sputtering gas. Compared with Ar or Ne sputtering gas, polycrystalline Zn3N2 films deposited using He sputtering gas have a larger grain size. The optical band gap of the Zn3N2 films varied from ∼1.2 to 1.5 eV depending on the N2 flow ratio and type of sputtering gas. The maximum mobility was 91.1 cm2/Vs when the Zn3N2 film was deposited using Ar sputtering gas with an N2 flow ratio of 40%. The carrier density of Zn3N2 films deposited using Ar sputtering gas was notably higher than those deposited using Ne or He sputtering gas, and more oxygen atoms are considered to substitute into nitrogen sites, where oxygen is considered to be from the residual water vapor in the sputtering chamber.

Sputter-deposited TiO2 films with high visible-light photocatalytic activity were successfully realized by a hybrid TiO2/Pt/WO3 film structure with Pt nanoparticles uniformly distributed at the interface of the TiO2 and WO3 films. The TiO2/Pt/WO3 hybrid films enable the complete decomposition of CH3CHO under visible-light irradiation. The water contact angle of the TiO2/Pt/WO3 hybrid films reaches below 51 under visible-light irradiation. Pt nanoparticles are considered to act as a cocatalyst to improve the electron-hole separation efficiency. We demonstrate that the photogenerated holes in WO3 are transferred to the surface of the TiO2 film with less hole-trapping and induce high visible-light photocatalytic activity and hydrophilic behavior, and the photogenerated electrons are accumulated in the Pt nanoparticles. The highly hydrophilic thin films with high visible-light photocatalytic activity can be applied to various indoor products possessing self-cleaning and antifogging properties.

The influence of dislocation density and impurities on the thermal conductivity of epitaxial GaN thin films on c-plane sapphire substrates was studied. GaN thin films with nominal thicknesses of 100, 300, and 1500 nm were fabricated by reactive direct current magnetron sputtering using a Ga metal target and a mixture gas of Ar and N-2. A 300-nm-thick GaN film was also fabricated using a mixture gas of Ar-N-2-H-2. For all the 300- and 1500-nm-thick films, epitaxial growth was confirmed from the sixfold symmetry spots in the pole figure and selected area electron diffraction patterns. Rocking curves of GaN(0002) of these films showed highly oriented growth along the c-axis. The dislocation density deduced from the rocking curves of GaN(10 (1) over bar0) ranged from 10 11 to 10(12) cm(-2). In the cases where a mixture gas of Ar-N-2 was used, films included O and H impurities on the order of 10(22) atoms cm(-3) in a layer of approximately 50-100 nm thickness near the substrate, and a low-impurity region with impurities on the order of 10(21) atoms cm(-3) existed above the high-impurity region. The addition of H-2 to the sputtering gas led to a reduction in the impurity concentration to a level on the order of 10(21) atoms cm(-3); it also prevented the formation of the high-impurity region near the substrate. The thermal conductivity of GaN thin films on c-plane sapphire substrates was measured by the pulsed-light-heating thermoreflectance method. The thermal conductivity of the low-impurity region in the 300-and 1500-nm-thick films ranged from 14 to 18W m(-1) K-1. The dislocation density and the oxygen impurities in our films were attributed to inhibitory factors of the thermal conductivity. The breakdown of the bonding network caused by the formations of Ga-NH2 and Ga-OH was not a negligible inhibitory factor of heat conduction. (C) 2017 American Vacuum Society.

High-quality transparent conductive oxide (TCO) films, Sn-doped In2O3 (ITO) and In2O3-ZnO (IZO), were successfully deposited on either synthetic silica or polyethylene terephthalate ( PET) substrates in the "transition region" by reactive dc magnetron sputtering using In-Zn and In-Sn alloy targets, respectively, with a specially designed plasma emission feedback system. The composition, crystallinity, surface morphology, and electrical and optical properties of the films were analyzed. All of the IZO films were amorphous, whereas the ITO films were polycrystalline over a wide range of deposition conditions. The minimum resistivities of the IZO and ITO films deposited on the heated PET substrates at 150 degrees C were 3.3 x 10%(-4) and 5.4 x 10%(-4) Omega.cm, respectively. By applying rf bias to unheated PET substrates, ITO films with a resistivity of 4.4 x 10%(-4) Omega.cm were deposited at a dc self-bias voltage of -60 (C) 2017 The Japan Society of Applied Physics

Indium-tin-zinc oxide ( ITZO) films were deposited at various nitrogen flow ratios using magnetron sputtering. At a nitrogen flow ratio of 40%, the structure of ITZO film changed from amorphous, with a short-range-ordered In2O3 phase, to a c-axis oriented InN polycrystalline phase, where InN starts to nucleate from an amorphous In2O3 matrix. Whereas, nitrogen addition had no obvious effect on the structure of indium-gallium-zinc oxide ( IGZO) films even at a nitrogen flow ratio of 100%. Nitrogen addition also suppressed the formation of oxygen-related vacancies in ITZO films when the nitrogen flow ratio was less than 20%, and higher nitrogen addition led to an increase in carrier density. Moreover, a red-shift in the optical band edge was observed as the nitrogen flow ratio increased, which could be attributed to the generation of InN crystallites. We anticipate that the present findings demonstrating nitrogen-addition induced structural changes can help to understand the environment-dependent instability in amorphous IGZO or ITZO based thin-film transistors ( TFTs). (C) 2016 Elsevier B.V. All rights reserved.

In this study, we focused on the origin on the selective deposition of rutile and anatase TiO2 thin films during the sputtering process. The observation on microstructural evolution of the TiO2 films by transmission electron microscopy revealed the coexistence of rutile and anatase TiO2 phases in the initial stage under the preferential growth conditions for the anatase TiO2
the observations further revealed that the anatase phase gradually dominated the crystal structure with increasing film thickness. These results suggest that the bombardment during the sputtering deposition did not obviously affect the TiO2 crystal structure, and this was also confirmed by off-axis magnetron sputtering experiments. We also investigated the mechanism of the effect of Sn impurity doping on the crystal structure using first-principles calculations. It is found that the formation energy of Sn-doped rutile TiO2 is lower than that of Sn-doped anatase TiO2
this suggests that the Sn-doped TiO2 favours the rutile phase. These results offer a guideline for the utilization of selective deposition of rutile and anatase TiO2 thin films in various industrial applications.

The influence of dopant species and concentration on the grain boundary scattering of differently doped In2O3 thin films is studied by means of room temperature and temperature dependent Hall effect measurements. Barrier heights at grain boundaries E-B are evaluated from temperature dependent carrier mobility taking the theoretically calculated temperature dependence of intragrain mobility into account. It is thereby shown that also samples with a negative temperature coefficient of mobility exhibit significant grain boundary barrier heights and that E-B is usually underestimated when evaluated based on Seto's model. It is also shown that the most commonly used Sn doping of In2O3 with a dopant concentration &gt;2 wt.% SnO2 leads to significantly enhanced grain boundary scattering compared to nominally undoped, Zr-doped and H-doped films. An effect of grain boundary scattering is even observed for carrier concentrations similar to 10(21) cm(-3) if the films exhibit a pronounced (100) texture. The poor grain boundary properties of highly Sn-doped In2O3 are attributed to segregation of the Sn dopants, which is also indicated by measurements of surface Sn concentration. (C) 2016 Elsevier B.V. All rights reserved.

Structural evolution of transparent conductive In2O3-ZnO (IZO) films with increasing substrate temperature during sputtering was studied using transmission electron microscopy (TEM) and spectroscopic ellipsometry. Increasing the substrate temperature can induce film crystallization in the initial growth stage, and enhance the crystallization of IZO films. Extensive simulations using ellipsometry data demonstrated a decrease in the crystallization rate for IZO films deposited between 200 and 300 degrees C, which is attributed to the influence of the interference between nearby growing grains. TEM observations also reveal that the growth competition between different crystallites leads to an increase in the lateral grain size with increasing substrate temperature. (C) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Homologous In2O3(ZnO)(5) thin films were produced on a synthetic quartz glass substrate by thermal annealing of magnetron sputtered In2O3-ZnO compound films. When the annealing temperature was increased to 700 degrees C, the sputtered In2O3-ZnO film with In2O3 microcrystalline changed to a c-oriented homologous In2O3(ZnO)(5) structure, for which the crystallization is suggested to begin from the surface and proceed along with the film thickness. The annealing temperature of 700 degrees C to form the In2O3(ZnO)(5) structure was substantially lower than temperatures of conventional solid state synthesis from In2O3 and ZnO powders, which is attributed to the rapid diffusional transport of In and Zn due to the mixing of In2O3 and ZnO in the atomic level for sputtered In2O3-ZnO compound films. The homologous structure collapsed at temperatures above 900 degrees C, which is attributed to (1) zinc vaporization from the surface and (2) a gradual increase of zinc silicate phase at the interface. This c-oriented layer structure of homologous In2O3(ZnO)(5) thin films along the film thickness allowed the thin film to reach a power factor of 1.3 x 10(-4) W/mK(2) at 670 degrees C, which is comparable with the reported maximum value for the textured In2O3(ZnO)(5) powder (about 1.6 x 10(-4) W/mK(2) at 650 degrees C). (C) 2016 American Vacuum Society.

In this study, we focused on the origin on the selective deposition of rutile and anatase TiO2 thin films during the sputtering process. The observation on microstructural evolution of the TiO2 films by transmission electron microscopy revealed the coexistence of rutile and anatase TiO2 phases in the initial stage under the preferential growth conditions for the anatase TiO2; the observations further revealed that the anatase phase gradually dominated the crystal structure with increasing film thickness. These results suggest that the bombardment during the sputtering deposition did not obviously affect the TiO2 crystal structure, and this was also confirmed by off-axis magnetron sputtering experiments. We also investigated the mechanism of the effect of Sn impurity doping on the crystal structure using first-principles calculations. It is found that the formation energy of Sn-doped rutile TiO2 is lower than that of Sn-doped anatase TiO2; this suggests that the Sn-doped TiO2 favours the rutile phase. These results offer a guideline for the utilization of selective deposition of rutile and anatase TiO2 thin films in various industrial applications.

SnO2 films doped with antimony or tantalum were sputter-deposited for comparison, using an identical set of parameters. The influence of dopant concentration and choice of deposition parameters such as substrate temperature on the optoelectronic properties, especially film resistivity, were determined. Comparative analysis shows that tantalum doping yields lower film resistivity, probably due to an increased inhibiting influence of grain boundary scattering in the case of antimony doping. Sputter-deposited tantalum-doped films with lower than previously achieved resistivity 5.4 x 10(-4) Omega cm, carrier density 4.5 x 10(20) cm(-3), and mobility 25.7 cm(2) Vs(-1) are reported, while maintaining optical transmittance above 85% at a film thickness 400 nm. Ta/Sb co-doped thin films were synthesized for the first time, achieving similar results. (C) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

By varying the density of solution-processed lithium fluoride (sol-LiF) nanoparticles at the interface between tin-doped indium oxide (ITO) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), we have demonstrated that the electronic hole collection efficiency of an organic photovoltaic cell can be optimized through tuning the energy level alignment at the ITO/PEDOT:PSS interface. We synthesized the LiF nanoparticles in solution and deposited them onto ITO electrodes with increasing surface coverage up to 13.2 %. The surface work function of the nanostructured ITO increased linearly from 4.88 to 5.30 eV. When the sol-LiF-modified ITO electrodes were incorporated into polymer solar cells based on a bulk heterojunction of poly(3-hexylthiophene) polymer and methanofullerene, a maximum power conversion efficiency was recorded for a device with an ITO anode modified by 5.3 % of sol-LiF coverage, which corresponded to a measured work function of 5.07 eV. The improvement in short circuit current density by 87 % and power conversion efficiency by 74.3 % suggest that the sol-LiF interlayer density enabled work function tuning of the ITO anode to better match the highest occupied molecular orbital level of PEDOT:PSS, facilitating hole charge collection. The increase in electronic hole collection efficiency is attributed to both a lowered resistance at the ITO modified by sol-LiF and faster hole transport, although these gains are offset by an associated increase in contact polarization. Our findings suggest that the surface work function of ITO can be tuned to improve energy level alignment with other contact layers via the surface density of sol-LiF particles. More efficient hole transport, due to higher recombination resistance, offset by an increased charge extraction barrier presented by contact polarization; the two effects combined give rise to an optimum in sol-LiF nanostructuring of the ITO surface properties.

A process based on reactive gas flow sputtering (GFS) for depositing visible-light active photocatalytic WO3 films at high deposition rates and with high film quality was successfully demonstrated. The deposition rate for this process was over 10 times higher than that achieved by the conventional sputtering process and the process was highly stable. Furthermore, Pt nanoparticle-loaded WO3 films deposited by the GFS process exhibited much higher photocatalytic activity than those deposited by conventional sputtering, where the photocatalytic activity was evaluated by the extent of decomposition of CH3CHO under visible light irradiation. The decomposition time for 60 ppm of CH3CHO was 7.5 times more rapid on the films deposited by the GFS process than on the films deposited by the conventional process. During GFS deposition, there are no high-energy particles bombarding the growing film surface, whereas the bombardment of the surface with high-energy particles is a key feature of conventional sputtering. Hence, the WO3 films deposited by GFS should be of higher quality, with fewer structural defects, which would lead to a decrease in the number of centers for electron-hole recombination and to the efficient use of photogenerated holes for the decomposition of CH3CHO. (C) 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

TiO2 films with various Sn concentrations were deposited on quartz substrates using rf reactive magnetron sputtering. The crystal structure was investigated by using x-ray diffraction, Raman spectroscopy, and transmission electron microscopy, and the chemical states of Ti and Sn were analyzed by x-ray absorption near edge structure (XANES) spectroscopy. Without Sn doping, TiO2 films change the crystal structure from rutile to anatase as the total gas pressure increases in the sputtering deposition. On the other hand, Sn doping induces the transformation of TiO2 crystalline structure from anatase to rutile phase, where the XANES spectra implied that Sn substitutes into Ti site of rutile TiO2. Atomic force microscope analyses revealed that the Sn-doped TiO2 films exhibited a flat surface with the roughness of approximately 2 nm. (C) 2015 American Vacuum Society.

Thermal conductivity of a 300-nm-thick VO2 thin film and its temperature dependence across the metal-insulator phase transition (TMIT) were studied using a pulsed light heating thermoreflectance technique. The VO2 and Mo/VO2/Mo films with a VO2 thickness of 300nm were prepared on quartz glass substrates: the former was used for the characterization of electrical properties, and the latter was used for the thermal conductivity measurement. The VO2 films were deposited by reactive rf magnetron sputtering using a V2O3 target and an Ar-O-2 mixture gas at 645 K. The VO2 films consisted of single phase VO2 as confirmed by X-ray diffraction and electron beam diffraction. With increased temperature, the electrical resistivity of the VO2 film decreased abruptly from 6.3 x 10(-1) to 5.3 x 10(-4) Omega cm across the T-MIT of around 325-340 K. The thermal conductivity of the VO2 film increased from 3.6 to 5.4W m(-1) K-1 across the T-MIT. This discontinuity and temperature dependence of thermal conductivity can be explained by the phonon heat conduction and the Wiedemann-Franz law. (C) 2015 The Japan Society of Applied Physics

This work presents the spatial distribution of electrical characteristics of amorphous indium-tinzinc oxide film (a-ITZO), and how they depend on the magnetron sputtering conditions using O-2, H2O, and N2O as the reactive gases. Experimental results show that the electrical properties of the N2O incorporated a-ITZO film has a weak dependence on the deposition location, which cannot be explained by the bombardment effect of high energy particles, and may be attributed to the difference in the spatial distribution of both the amount and the activity of the reactive gas reaching the substrate surface. The measurement for the performance of a-ITZO thin film transistor (TFT) also suggests that the electrical performance and device uniformity of a-ITZO TFTs can be improved significantly by the N2O introduction into the deposition process, where the field mobility reach to 30.8 cm(2) V-1 s(-1), which is approximately two times higher than that of the amorphous indium-gallium-zinc oxide TFT. (C) 2015 AIP Publishing LLC.

We observed the carrier transport phenomena in polycrystalline Al-doped ZnO (AZO) films with carrier densities ranging from 2.0 x 10(19) to 1.1 x 10(21) cm(-3). A comparison of the optical carrier density and Hall carrier density indicates that the conduction band in AZO films is nonparabolic above 2.0 x 10(20) cm(-3). A transition from grain boundary scattering to ionized impurity scattering is observed at a doping level of x 10(20) cm(-3). The trap density at the grain boundary increases with increasing Al concentration in the films, implying that the doping level plays a decisive role in the trap density. The excellent fitting of the optical mobility and carrier density using the Brooks-Herring model shows that the acceptor concentration increases with increasing doping level. (C) 2014 The Japan Society of Applied Physics

We investigate the effect of dopant species and structure on the thermal conductivity of Sb-doped SnO2 (ATO) and Ta-doped SnO2 (TTO) films and compare the results with those of In2O3-, ZnO-, and TiO2-based transparent conductive films. The thermal conductivities (lambda) of polycrystalline ATO and TTO films are 4.4-4.9 and 4.7 W m(-1) K-1, respectively. The thermal conductivities via phonons (lambda(ph)) are almost identical for both dopant species (Sb and Ta): 4.3 and 4.5 W m(-1) K-1 for Sb and Ta, respectively, on average. These results for lambda(ph) are larger than that for Sn-doped In2O3 films (3.8 W m(-1) K-1) and considerably larger than that for amorphous ATO films (1.0 W m(-1) K-1). These facts lead us to conclude that the base-material species (SnO2 or In2O3) and structure (polycrystalline or amorphous) affect the thermophysical properties of ATO and TTO much more than the dopant species.

In this study, a stable reactive sputtering process using a Ti-Nb alloy target was achieved by applying a plasma impedance feedback system. High-quality transparent conductive Nb-doped TiO2 (Nb:TiO2) films were fabricated with high reproducibility. The films were deposited on unheated substrate and subsequently annealed at 873 K under vacuum conditions (below 6.0 x 10(-4) Pa) for 1 h. During reactive sputtering, the feedback system precisely controlled the oxidation of the target surface in the so-called transition region. The post-annealing process yielded polycrystalline Nb:TiO2 films whose lattice defects decreased with increasing Nb concentration. An extremely low resistivity (7.2 x 10(-4) Omega cm) was achieved for Nb:TiO2 film with 60-70% transmittance in the visible region. The reactive sputtering using Ti-Nb alloys is considered to be a strong candidate for industrial-scale thin-film deposition. Furthermore, it can also control the metal-oxygen stoichiometry of Nb:TiO2 films precisely to achieve desirable properties for each industrial application. (C) 2014 Elsevier B.V. All rights reserved.

Al and Ga doped ZnO (AZO and GZO) films were deposited using an off-axis dc magnetron sputtering method. At the off-axis positions, both the mobility and carrier density increased, resulting in enhanced conductivity of both the AZO and GZO films due to an increase in the crystallinity. The lowest resistivities of the AZO and GZO films deposited at room temperature were 1.1 x 10(-3) Omega cm and 6.5 x 10(-4) Omega cm, respectively. Increasing the substrate temperature up to 130 C led to a decrease in the lowest resistivity to 6.1 x 10(-4) Omega cm for the AZO films. The transmittance of all films was above 80% in the visible region. These results suggest that off-axis magnetron sputtering might be a potentially effective deposition method with the reduced bombardments from high-energy particles. (C) 2014 Elsevier B. V. All rights reserved.

Amorphous indium-zinc-oxide films were deposited in the "transition region" by reactive sputtering using an In-Zn alloy target with a specially designed double feedback system. The cathode voltage showed a V-and circle-shaped curve as a function of O-2 gas flow in the transition region, which differs from the S-shaped curve in Berg's model for reactive sputtering depositions. In-situ analyses with a quadrupole mass spectrometer combined with an energy analyzer revealed that the negative ions O-, O-2(-), InO-, and InO2-, with high kinetic energies corresponding to the cathode voltage, were generated at the partially oxidized target surface. Furthermore the positive ions O+, Ar+, In+, and Zn+ with rather low kinetic energies (around 10 eV) were confirmed to be generated by the charge exchange of sputtered neutral O, Ar, In and Zn atoms, respectively. (C) 2013 Elsevier B.V. All rights reserved.

Solution-processed lithium fluoride (sol-LiF) nanoparticles synthesized in polymeric micelle nanoreactors enabled tuning of the surface work function of tin-doped indium oxide (ITO) films. The micelle reactors provided the means for controlling surface coverage by progressively building up the interlayer through alternating deposition and plasma etch removal of the polymer. In order to determine the surface coverage and average interparticle distance, spatial point pattern analysis was applied to scanning electron microscope images of the nanoparticle dispersions. The work function of the sol-LiF modified ITO, obtained from photoelectron emission yield spectroscopy analysis, was shown to increase with surface coverage of the sol-LiF particles, suggesting a lateral depolarization effect. Analysis of the photoelectron emission energy distribution in the near threshold region revealed the contribution of surface states for surface coverage in excess of 14.1%. Optimization of the interfacial barrier was achieved through contributions from both work function modification and surface states. (C) 2013 Elsevier B.V. All rights reserved.

Al-doped ZnO (AZO) films were deposited on a fused silica glass substrate by reactive dc unbalanced magnetron sputtering using a Zn-Al (Al: 3.6 at.%) alloy target with an impedance control system. A very thin slightly reduced AZO buffer layer was inserted between the glass substrate and AZO films. For the AZO films deposited at 200 degrees C, the lowest resistivity in the absence of the buffer layer was 8.0 x 10(-4) Omega cm, whereas this was reduced to 5.9 x 10(-4) Omega cm after introducing a 5-nm-thick buffer layer. The transmittance for all the films was above 80% in the visible region. The effects of the buffer layer were analysed and discussed in detail. It is found that the insertion of the buffer layer can improve the crystallinity of the AZO film. (C) 2013 Elsevier B.V. All rights reserved.

We investigated the dependence of the thermal boundary resistance of the W/Al2O3 interface in W/Al2O3/W three-layered thin films on the interface morphology. The layered structures, Al2O3 thin layers with thicknesses from 1 to 50nm covered by top and bottom W layers with a thickness of 100 nm, were fabricated by magnetron sputtering using a W target (99.99%) and an Al2O3 target (99.99%). The fabrication of polycrystalline W and amorphous Al2O3 films was confirmed by structural analysis. The morphology of the bottom W layer/Al2O3 layer and Al2O3 layer/top W layer interfaces showed a wavelike structure with a roughness of about 1 nm. Thermophysical properties and thermal boundary resistance were measured by a pulsed light heating thermoreflectance technique. The thermal boundary resistance of the W/Al2O3 interface was 1.9 x 10(-9) m(2)K W-1, which corresponds to the thermal resistance of a 3.7-nm-thick Al2O3 film or a 120-nm-thick W film. (C) 2013 The Japan Society of Applied Physics

We investigated the dependence of valence-and core-level photoemission spectra of amorphous In2O3-ZnO (a-IZO) films on carrier density by using hard x-ray photoemission spectroscopy (h nu = 8000 eV). The valence band edge distinctly shifts toward high binding energy with the increase in carrier density from 0.80 to 3.96 x 10(20) cm(-3), and an abrupt jump for the shift of the valence band edge from high to low binding energy occurs at a carrier density of 4.76 x 10(20) cm(-3). After considering the effect of nonparabolic bandstructure, the shifts are still less than the width of the occupied conduction band, providing direct evidence for the band gap shrinkage. Our calculation results indicate that the contribution of the band gap shrinkage increases as the carrier density increases, which accords with the observations in doped conducting crystal materials, such as Sn doped In2O3. Moreover, it is found that the conduction electrons of a-IZO films are strongly perturbed by the ionization of core levels, which leads to obvious plasmon satellites in core photoemission spectra lines. (C) 2013 AIP Publishing LLC

We investigated the thermal conductivity of 200-nm-thick amorphous indium-gallium-zinc-oxide (a-IGZO) films. Films with a chemical composition of In : Ga : Zn = 1 : 1 : 0.6 were prepared by dc magnetron sputtering using an IGZO ceramic target and an Ar-O-2 sputtering gas. The carrier density of the films was systematically controlled from 10(14) to &gt; 10(19) cm(-3) by varying the O-2 flow ratio. Their Hall mobility was slightly higher than 10 cm(2) .V-1 .s(-1). Those films were sandwiched between 100-nm-thick Mo layers; their thermal diffusivity, measured by a pulsed light heating thermoreflectance technique, was similar to 5.4 x 10(-7) m(2) .s(-1) and was almost independent of the carrier density. The average thermal conductivity was 1.4W.m(-1) .K-1. (C) 2013 The Japan Society of Applied Physics

A Brownian dynamics simulation has been used to investigate the aggregation kinetics of bimodal colloidal mixtures with similar surface chemistries but different sizes, driven by the DLVO interaction potential. The time evolution of structural formation is examined by the mean number of neighbors under fast and slow aggregation regions. It was found that the electrolyte ionic strength affects the kinetic pattern of colloidal aggregation. Under the high electrolyte ionic strength conditions (fast aggregation), the selective aggregation of the least stable single component can take place in the early stage, while the other component is enriched in this least stable component in the later stage. With the ionic strength decreasing (towards the slow aggregation), the hybrid aggregation (selective aggregation and heteroaggregation) gradually dominates the aggregation kinetics. Also in the early stage, this evolves to the heteroaggregation of different components under lower ionic strength conditions. The volume fraction has no obvious influence on this kinetic pattern in the early stage. (C) 2011 Elsevier Inc. All rights reserved.

The nonequilibrium aggregation structure of primary particles in colloidal bidispersions is investigated at high volume fractions by Brownian dynamics simulations. It is found that introducing limited different sized particles in the monodispersion can obviously affect the short-range structures of primary particles. In a bidispersion, fractal dimension of aggregates, only consisting of primary particles, increases with increasing the size difference in the long-range scale. The structure factor S(q) of aggregates, obtained from the particle correlation function g(r), suggests that fractal structure disappears when the primary particles become not "primary" in volume fraction.