Transparent amorphous conductive Cd-In-Sb-O thin films for flexible devices

Transparent conductive amorphous Cd-In-Sb-O thin films were deposited on a flexible polyethylene naphthalate film by rf magnetron sputtering at room temperature. The large Hall mobility of ∼26 cm² V⁻¹ s⁻¹ was observed on the films with carrier density >10²⁰ cm⁻³. The carrier density varied from the order of 10²⁰ to 10¹⁷ cm⁻³ with increasing the oxygen partial pressure. The Hall mobility reached up to ∼17 cm² V⁻¹ s⁻¹, even at carrier density of ∼10¹⁷ cm⁻³. Flexible transparent filed-effect transistor was also fabricated using the Cd-In-Sb-O thin films as a channel layer and the device performance was investigated. The device exhibited a field-effect mobility of ∼0.45 cm² V⁻¹ s⁻¹ and an on-off ratio of ∼10² at room temperature.     

Organic semiconductor based on phenylethynyl end-capped anthracene

Organic semiconductor based on anthracene with phenylethynyl end capping units, which has rigid rod-like structure with high aspect ratio, was synthesized by Sonogashira coupling reaction. The structure of obtained material was confirmed by fourier transform infrared spectroscopy, mass and elemental analysis and its physical properties were characterized by ultraviolet-visible spectroscopy and cyclovoltammetry. 2,6-Bis-phenylethynyl-anthracene (BPEA) has deeper highest occupied molecular orbital level with higher stability as well as high intermolecular π-π stacking. The crystalline and morphological properties of BPEA thin film were studied using X-ray diffraction and atomic force microscopy. BPEA forms high long range ordered structure in the film and it exhibited high field effect mobility of 0.42 cm² V^− 1 s^− 1 (on/off ratio of 10⁷) with device reproducibility and high oxidation stability.     

Thin-film transistors with sol-gel deposited Mg0.1Zn0.9O films as active channel layer

We report on field-effect transistors using Mg_0.1Zn_0.9O thin film as channel layer. The effect of Mg is to increase the band gap and decrease the electron carrier concentration. The Mg_0.1Zn_0.9O film deposited by sol-gel method has a highly c-axis orientation and excellent optical properties. The devices display a channel mobility of 0.76 cm² V^− 1 s^− 1 and an on/off ratio of 400.     

Conductive and photovoltaic properties of multilayered ultrathin films designed by layer-by-layer assembly of titanium oxides

Titania-based ultrathin films were fabricated by layer-by-layer (LbL) assembly of titanium (IV) bis(ammonium lactato) dihydroxide (TALH) and polyelectrolytes. The thickness of the titania monolayer in the LbL films was 4-5 nm, which was consistent with the particle size of TALH in water. The conductivity and the electron mobility of the LbL films reached 10^− 8 S cm^− 1 and 10^− 5 cm² V^− 1 s^− 1, respectively. These results suggest that there exist percolation paths for the electron transport in the LbL film. Furthermore, it is demonstrated that photovoltaic properties of the LbL film can serve as an effective electron-transporting and accepting layer.     

Ammonia-free chemically deposited CdS films as active layers in thin film transistors

In this work we have grown CdS thin films using an ammonia-free chemical bath deposition process for the active layer in thin film transistors. The CdS films were deposited substituting sodium citrate for ammonia as the complexing agent. The electrical characterization of the as-deposited CdS-based thin film transistors shows that the field effect mobility and threshold voltage were in the range of 0.12-0.16 cm²V⁻¹ s⁻¹ and 8.8-25 V, respectively, depending on the channel length. The device performance was improved considerably after thermal annealing in forming gas at 250 °C for 1 h. The mobility of the annealed devices increased to 4.8-8.8 cm²V⁻¹ s⁻¹ and the threshold voltage decreased to 8.4-12 V. I_on/I_off for the annealed devices was approximately 10⁵-10⁶.     

Structural properties of low-temperature grown ZnO thin films determined by X-ray diffraction and X-ray absorption spectroscopy

The epitaxial growth of ZnO thin films on Al₂O₃ (0001) substrates have been achieved at a low-substrate temperature of 150 °C using a dc reactive sputtering technique. The structures and crystallographic orientations of ZnO films varying thicknesses on sapphire (0001) were investigated using X-ray diffraction (XRD). We used angle-dependent X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy to examine the variation of local structure. The XRD data showed that the crystallinity of the film is improved as the film thickness increases and the strain is fully released as the film thickness reached about 800 Å. The Zn K-edge XANES spectra of the ZnO films have a strong angle-dependent spectral feature resulting from the preferred c-axis orientation. The wurtzite structure of the ZnO films was explicitly shown by the XRD and EXAFS analysis. The carrier concentration, Hall mobility and resistivity of the 800 Å-thick ZnO film were 1.84 × 10¹⁹ cm^− 3, 24.62 cm²V^− 1s^− 1, and 1.38 × 10^− 2 Ω cm, respectively.     

Effect of process parameters on the growth and properties of impurity-doped zinc oxide transparent conducting thin films by RF magnetron sputtering

Zinc oxide transparent conducting thin films co-doped with aluminum and ruthenium were grown on polyethylene terephthalate substrates at room temperature using RF magnetron sputtering. The crystal growth and physical properties of the films were investigated with respect to the variation of discharge power density from 1.5 to 6.1 W/cm² and sputtering pressure from 0.13 to 2.0 Pa. X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) showed that the films grown with 3.6 W/cm² power density and sputtering pressure of 0.4 Pa had the best crystallinity and larger pyramid-like grains. The optimized electrical resistivity had a lowest measured value of about 9 × 10⁻⁴ Ω cm. The low carrier mobilities of the films (3-8.9 cm² V⁻¹ s⁻¹) have been discussed in terms of what is believed to be the dominant effect of ionized impurity scattering, but in addition chemisorption of oxygen on the film surface and effect of grain boundaries are also thought to be significant. The transmittances of the films in the visible range are greater than 80%, while the optical band gaps are in the order of 3.337-3.382 eV.     

Non-aqueous solution processed ZnO thin film transistors

Zinc oxide based thin film transistors (TFT) fabricated by a non-aqueous sol-gel solution process with a zinc neodecanoate precursor are demonstrated. X-ray diffraction measurement reveals that the ZnO films adopt a hexagonal structure with a random crystal orientation. Atomic force microscope and scanning electron microscope characterizations show that the films are closely packed and consisted of particles with an average size of 45 nm. The devices exhibit an n-channel enhancement mode behavior, with saturation mobility in the range of 0.95-1.29 cm² V⁻¹ s⁻¹, drain current on-to-off ratios higher than 10⁷ and threshold voltages between 5.3 and 16.8 V in an ambient environment. The results imply that high-performance ZnO TFTs produced by a simple and low-cost technique could be applicable to electronic devices.     

Transparent conducting Al and Y codoped ZnO thin film deposited by DC sputtering

Transparent conducting Al and Y codoped zinc oxide (AZOY) thin films with high transparency and low resistivity were deposited by DC magnetron sputtering. The effects of substrate temperature on the structural, electrical and optical properties of AZOY thin films deposited on glass substrates have been investigated. X-ray diffraction spectra indicate that no diffraction peak of Al₂O₃ or Y₂O₃ except that of ZnO (0 0 2) is observed. The AZOY thin film prepared at substrate temperature of 250 °C has the optimal crystal quality inferring from FWHM of ZnO (0 0 2) diffraction peak, but the AZOY thin film deposited at 300 °C has the lowest resistivity of 3.6 × 10⁻⁴ Ω-cm, the highest mobility of 30.7 cm² V⁻¹ s⁻¹ and the highest carrier concentration of 5.6 × 10²⁰ cm⁻³. The films obtained have disorderly polyhedral surface morphology indicating possible application in thin film solar cell with good quality and high haze factor without the need of post-deposition etching.     

Luminescence and electrical properties of solution-processed ZnO thin films by adding fluorides and annealing atmosphere

To develop an efficient channel layer for thin film transistors (TFTs), understanding the defect-related luminescence and electrical property is crucial for solution-processed ZnO thin films. Film growth with the fluorides addition, especially using LiF, followed by the oxygen ambient post-annealing leads to decreased defect-related emission as well as enhanced switching property. The saturation mobility and current on/off ratio are 0.31 cm² V⁻¹ s⁻¹ and 1.04 × 10³. Consequently, we can visualize an optimized process condition and characterization method for solution-processed TFT based on the fluorine-doped ZnO film channel layer by considering the overall emission behavior.