Hauk Han

Improved conductivity and mechanism of carrier transport in zinc oxide with embedded silver layer

The effects of an embedded silver layer on the electrical and optical properties of zinc oxide (ZnO)/silver (Ag)/zinc oxide (ZnO) layered composite structures on polymer substrates have been investigated. We have engineered transparent conducting oxide structures with greatly improved conductivity. Optical and electrical properties are correlated with Ag thickness. Film thicknesses were determined using Rutherford backscattering spectrometry. Hall effect, four-point probe, and UV-Vis spectrophotometer analyses were used to characterize electrical and optical properties. The results show that carrier concentration, mobility, and conductivity increase with Ag thickness. Increasing Ag thickness from 8to14nm enhances sheet resistance and resistivity by six orders of magnitude. The optical transmittance of the composite structure decreases when compared to a single ZnO layer of comparable thickness. However, a composite with 12nm of Ag provides conductivity and transmittance values that are acceptable for opto...

Band gap shift in the indium-tin-oxide films on polyethylene napthalate after thermal annealing in air

Indium-tin-oxide (ITO) thin films on polyethylene napthalate (PEN) with high carrier concentration (∼1021∕cm3) have been grown by electron-beam deposition without the introduction of oxygen into the chamber. The electrical properties of the ITO films (such as, carrier concentration, electrical mobility, and resistivity) abruptly changed after annealing in the air atmospheres. In addition, optical transmittance and optical band gap values significantly changed after heat treatment. The optical band gap narrowing behavior is observed in the as-deposited sample because of impurity band and heavy carrier concentration. The influence of annealing in air on the electrical and optical properties of ITO∕PEN samples can be explained by the change in the free electron concentration, which is evaluated in terms of the oxygen content. Rutherford backscattering spectrometry and x-ray photoelectron spectroscopy analyses are used to determine the oxygen content in the film. Hall effect measurements are used to determine...

Characterization of the physical and electrical properties of Indium tin oxide on polyethylene napthalate

Indium tin oxide (ITO) thin films, on polyethylene napthalate (PEN) of both good electrical and optical properties were obtained by radio-frequency sputtering. The optoelectronic properties of the ITO films on PEN substrate were evaluated in terms of the oxygen content and the surface morphology. Rutherford backscattering spectrometry analysis was used to determine the oxygen content in the film. Hall-effect measurements were used to evaluate the dependence of electrical properties on oxygen content. The results showed that the resistivity of the ITO film increases with increasing oxygen content. For an oxygen content of 1.6×1018–2.48×1018atoms∕cm2, the resistivity varied from 0.38×10−2to1.86×10−2Ωcm. Typical resistivities were about ∼10−3Ωcm. UV-Vis spectroscopy and atomic force microscopy measurements were used to determine the optical transmittance and surface roughness of ITO films, respectively. Optical transmittances of ∼85% were obtained for the ITO thin films. Our results revealed that substrate r...

Effect of various annealing environments on electrical and optical properties of indium tin oxide on polyethylene napthalate

The effect of different annealing ambients on the electrical and optical properties of indium tin oxide (ITO) on polyethylene napthalate (PEN) has been investigated. ITO layers of different carrier concentrations have been prepared by radio frequency sputtering followed by annealing in either 5% H2∕Ar, oxygen, or air at 150°C for 2h. The carrier concentration of the ITO films increased with heat treatment in the 5% H2∕Ar ambient. However, the carrier concentration of the ITO films decreased with heat treatment in oxygen and air atmospheres, respectively. Different annealing ambients affect the electrical properties of ITO/PEN samples by changing the oxygen vacancy in the ITO layer. Electrical mobilities were found to be affected by the carrier concentration. These experimental mobility values were in good agreement with those obtained from a theoretical ionized impurity scattering mechanism model. Optical transmittances of ∼86% were obtained for the ITO thin films and the optical band gap is about 3.15eV ...

Influence of defects and processing parameters on the properties of indium tin oxide films on polyethylene napthalate substrate

Indium tin oxide (ITO) thin films were deposited on polyethylene napthalate (PEN) by rf sputtering using different rf powers (60 and 120W) and at different substrate temperatures (room temperature and 100°C). Selected PEN substrates were pretreated using an Ar plasma before ITO sputter deposition. Rutherford backscattering spectrometry was used to determine the oxygen content in the films. Hall effect measurements were used to evaluate the electrical properties. In this paper the influence of defect structure, sputtering conditions, and the effect of annealing on the electrical and optical properties of ITO on PEN have been investigated. Electrical properties such as carrier concentration, mobility, and resistivity of the ITO films varied with rf power and substrate temperature. The electrical and optical properties of the films changed after annealing in air. This study also describes how the as-deposited amorphous ITO changes from amorphous to crystalline as a result of heat treatment, and investigates ...

Improved surface morphology and texture of Ag films on indium tin oxide via Cu additions

The surface and texture properties of Ag(Cu) alloy thin films on indium tin oxide (ITO) has been investigated and compared to pure Ag thin films on ITO. Atomic force microscopy (AFM) and x-ray diffraction results of annealed films show differences in the evolution of surface morphology and texture with annealing. The presence of Cu atoms in the silver alters the alloy’s surface energy and surface diffusion. This results in Ag and Ag(Cu) alloy having the very different surface morphology and crystallographic texture. The (111) texture of the Ag(Cu) is enhanced when compared to that of pure Ag films. The resistivity of Ag(Cu) films annealed at high temperatures (∼up to 600°C for 1h in vacuum) remained constant due to absence of agglomeration.

Copper enhanced (111) texture in silver thin films on amorphous SiO2

Small amounts (5at.%) of copper were added to silver thin films to improve adhesion and minimize agglomeration on SiO2 layers. Resistivity measurements from the Ag(Cu) films showed that small Cu additions do not significantly increase the resistivity compared to pure Ag. Texture evolution and surface morphology of Ag and Ag(Cu) thin films on SiO2 were also investigated using x-ray diffraction (XRD) techniques and atomic force microscopy. Normalized (111) θ-2θ XRD intensities increased from 91.6% to 96.8% upon addition of Cu, likely due to enhanced adatom diffusion resulting from the Cu addition. XRD pole figure analysis revealed differences in texture evolution between the Ag and Ag(Cu) thin films. Since high adatom surface diffusion of Cu promotes preferred grain growth of the Ag matrix, Ag(Cu) thin films showed enhanced (111) texture compared to Ag thin films. Glancing angle XRD results confirmed the evolution of (111) texture in the Ag and Ag(Cu) thin films. In the case of Ag, (111) texture was enhance...

Influence of Metal Impurity Defects on the Electrical and Optical Properties of ITO Films on the PEN Substrates

Indium tin oxide (ITO) has drawn a great deal of attention due to its potential use as transparent electrodes in organic light emitting diode (OLED) and photovoltaic applications. This work focuses on understanding the role of impurity defects on the electrical conduction and transmittance of ITO. Thin films of ITO with high carrier concentration have been deposited onto polyethylene napthalate (PEN) substrates by electron-beam deposition without introduction of oxygen into the chamber. The influence of air anneals on the electrical and optical properties of ITO/PEN samples can is evaluated in terms of the oxygen content and is explained in terms of changes in the free electron concentrations. Rutherford backscattering spectrometry and X-ray photoelectron spectroscopy analysis were used to determine the oxygen content in the film. A Hall effect measurement is used to determine the dependence of electrical properties on oxygen content. The electrical properties of the ITO films such as carrier concentration, electrical mobility, and resistivity abruptly changes after annealing in the air atmospheres. In addition, optical transmittance is improved from 7 to 71 % and optical band gap changes from 3.18 to 3.25 eV after heat treatment. The optical band gap narrowing behavior is because of impurity band and heavy carrier concentration. Metal impurity clusters form in the films as a result of oxygen deficiency and also generate defects and/or impurity states in the band gap and produces an optical band gap shift by merging of these impurity states and conduction band.

Tailoring electrical conductivity and mechanism of carrier transport in zinc oxide with embedded Ag layer

The effects of an embedded silver layer on the electrical properties of zinc oxide (ZnO) / silver (Ag)/ zinc oxide (ZnO) layered composite structures on polymer substrates have been investigated. We have engineered transparent conducting oxide structures with greatly improved conductivity. Electrical properties are correlated with Ag thickness. Film thicknesses were determined using Rutherford backscattering spectrometry. Hall effect, 4-point probe, and UV-Vis spectrophotometer analyses were used to characterize electrical and optical properties. The results show that carrier concentration, mobility, and conductivity increase with Ag thickness. Increasing Ag thickness from 8 to 14 nm enhances sheet resistance and resistivity by six orders of magnitude. We describe of the influence of Ag thickness on electrical properties of the ZnO/Ag/ZnO composite and propose a conduction mechanism for this system.