Jie Shen

A new transparent conductive thin film In2O3:Mo

Abstract A new high quality transparent conductive thin film In2O3:Mo (IMO) was prepared by conventional thermal reactive evaporation at the substrate temperature of approximately 350°C. From X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) analysis of IMO films, it was confirmed that Mo6+ substituted In3+ without changing the cubic bixbyite structure of In2O3 and there were no new compounds in IMO as well. One atom of dopant contributes with more electrons to the electrical conductivity and at the same carrier concentration there is fewer dopant in IMO than in other doped oxides. So, the IMO film exhibits simultaneously higher values of Hall mobility, electric conductivity, visible light transmittance, infrared reflectance and plasma wavelength. An electrical resistivity as low as 1.7×10−4 Ω cm was obtained, while the infrared reflectance above 4 μm and the average total visible light transmittance of the IMO film plus the glass substrate were both over 80%, and the plasma wavelength was at approximately 2.2 μm. IMO is more suitable for the energy efficient windows used in cold climates or even for optoelectronic device applications.

Molybdenum-doped indium oxide transparent conductive thin films

We developed a novel transparent conductive film, molybdenum-doped indium oxide (IMO). Using normal thermal reactive evaporation without any special treatments, IMO films have been prepared on normal glass microscope slides at about 350 °C with electrical resistivity of 1.7×10−4 Ω cm, mobility over 100 cm2 V−1 s−1, and an average spectral transmittance in the visible region over 80%. From x-ray photoelectron spectroscopy and x-ray diffraction spectra of the IMO films, it is confirmed that the lattice of IMO is the same as that of In2O3 of cubic bixbyite structure, Mo6+ substitutes for In3+ in In2O3, and there are no new compounds in IMO. The valence difference of 3 between Mo6+ and In3+ is of great advantage to the IMO film with high conductivity and high transparency simultaneously.

Carrier concentration dependence of terahertz transmission on conducting ZnO films

With the dc reactive magnetron sputtering method, conducting ZnO thin films with different carrier concentrations on glass substrate were fabricated. The dielectric responses of the ZnO films are characterized with terahertz time-domain spectroscopy. Frequency-dependent conductivity, power absorption, and refractive index are obtained, and the experimental results can be well reproduced with the classic Drude model. Our results reveal that by adjusting the carrier concentration of the ZnO film, the conducting ZnO film can serve as broadband antireflection coatings for substrates and optics in the terahertz frequency range.

Electrical and optical properties of molybdenum-doped ZnO transparent conductive thin films prepared by dc reactive magnetron sputtering

Molybdenum-doped ZnO (ZMO) transparent conductive thin films were prepared by dc reactive magnetron sputtering on glass substrates from metallic targets. The structure, surface morphology, chemical state, optical and electrical properties of ZMO films were studied. The XRD pattern confirmed that ZMO thin films were polycrystalline with the hexagonal crystal structure, and the surface morphology measured by AFM demonstrated that the surface was smooth and compact. Chemical state analysis revealed that molybdenum atoms existed mainly in Mo6+ and Mo5+ ions but not in only single oxidation states. The minimum resistivity of 7.9 × 10−4 Ω cm is obtained with a carrier mobility of 27.3 cm2 V−1 s−1 and a carrier concentration of 3.1 × 1020 cm−3, and the average transmittance is more than 85% in the visible light region. The refractive index and extinction coefficient at the wavelength of 550 nm are 1.853 and 7.0 × 10−3, respectively. The energy bands increase from 3.37 eV to 3.8 eV with the increase in carrier concentrations and the carrier effective mass m* is 0.33 times the electron mass.

Defect-mode dependence of two-photon-absorption enhancement in a one-dimensional photonic bandgap structure

A one-dimensional photonic crystal containing a single CdS defect layer of various thicknesses was fabricated. The dependence of the two-photon-absorption (TPA) coefficient on the defect mode was investigated by use of a femtosecond pump-probe method. Experimental results show that the TPA coefficient of the CdS defect layer depends strongly on the defect mode in the photonic bandgap. This is consistent with the predicted dependence of light intensity within the defect layer.

Visible Light Photoelectrochemical Response of Carbon- Doped TiO2 Thin Films Prepared by DC Reactive Magnetron Sputtering

Carbon-doped TiO2 thin films were prepared by direct current (DC) reactive magnetron sputtering at room temperature in Ar/O2 ambience, using a titanium target incrusted with graphite pieces. The films as prepared were characterized by X-ray diffraction (XRD), UV-Vis transmission spectra, and photoelectrochemistry methods. The XRD patterns of the films showed that the doping of carbon was beneficial to the crystallization of the films. When the ratio of area of C/Ti was less than 0.10, the crystallization of the films increased with the increase in graphite area in the target. The band gap of the films decreased from 3.4 eV (pure TiO2 films) to 3.1 eV when the ratio of area of C/Ti in the target was 0.05. The photoelectrochemical property of the films improved when the ratio of area of C/Ti in the target was less than 0.10. When this ratio was 0.10, the photocurrent density of the films was 0.069 μA·cm−2 at 0 V under visible light illumination. However, an abnormal photoelectrochemical response was observed when the ratio of area of C/Ti in the target was 0.16.

Intense Photocurrent from Mo-Doped TiO2 Film with Depletion Layer Array

A novel bilayer structure of TiO2 film was found capable of yielding fairly strong photocurrent under visible light. The base layer was lightly doped with Mo and then etched by reactive ion beam, and was finally covered by an undoped TiO2 surface layer. Because of Fermi level drop at the interface of the trenches, such a deposition-etching-redeposition process implanted an array of depletion layer into TiO2 film successfully. Microstructures, crystallite parameters, and the absorption property were investigated with scanning electron microscope, atomic force microscopy, X-ray diffraction, and ultraviolet-visible spectroscopy in order. Photocurrent density was collected on an electrochemical workstation under visible light. The results indicate that carrier collection probability near depletion layer was enhanced significantly owing to high parallel diffusivity. Under visible light, current density demonstrates a marked increase as etching depth grows. At an etching depth around 660 nm, photocurrent density achieved is 56 times larger than TiO2 film. Depletion layer at vertical trench edges may have a much bigger universal value than anticipated for various doping cases of wide-bandgap films.

Observation of two-photon absorption enhancement at double defect modes in one-dimensional photonic crystals

One-dimensional photonic crystals (1D PC) with two CdS defect layers in a SiO2∕TiO2 dielectric thin film stack were fabricated. Two-photon absorption (TPA) coefficients of the CdS defect layers in the 1D PC were investigated using femtosecond pump-probe method. Significant enhancement of the TPA coefficient in the CdS defect layers was observed to occur at the two defect modes. Experimental results show that the enhanced TPA coefficient at the defect mode of 800nm is larger than that at the defect mode of 762nm. A numerical simulation by matrix transfer method is performed and agrees with the experimental results very well.

Ar plasma irradiation improved optical and electrical properties of TiO₂/Ag/TiO₂ multilayer thin film.

Embedding a thin metal layer between two thin dielectric or semiconductor layers [dielectric/metal/dielectric (DMD)] leads to a kind of transparent electrode that is promising as a substitute for the currently widely applied indium tin oxide electrode. However, the optical and electrical properties of DMD still wait for further improvement. In this study, Ar plasma irradiation (API) was, for the first time to our knowledge, applied to improve the optical and electrical properties of a TiO2/Ag/TiO2 electrode that was fabricated by electron-beam evaporation of TiO2 and electric-resistance heating of high purity Ag under vacuum. Ar plasma was produced by radio frequency glow discharge. The Ag layer was bombarded before the second layer of TiO2 was deposited. The electrode with configuration of TiO2 (24  nm)/Ag(14  nm)/TiO2 (24  nm) after API for 10 s shows excellent performance. The mean transmittance between 370 and 800 nm reaches 94% and the sheet resistance is as low as 6  Ω/sq, while Haackes figure of merit is as high as 112×10(-3)  Ω(-1). The improvement mechanism is discussed based on field emission scanning electron microscope images and absorption spectra. The improvement is attributed to the fact that API reduces the localized surface plasmon resonance of Ag nanoparticles and makes the Ag film thinner and denser.

Enhanced photocatalytic activity of C-TiO2 thin films prepared by magnetron sputtering and post-carbon ion implantation

TiO2 thin films were fabricated by RF magnetron sputtering on titanium substrates and then implanted with different amounts of carbon. The microstructure, valence states and optical characteristics of each sample were investigated by X-ray diffraction, X-ray photoelectron spectroscopy and UV-vis diffuse reflection spectroscopy. Photoelectric property was evaluated under visible light using a xenon lamp as illuminant. The experimental results indicate that the implanting carbon concentration has a significant influence on film’s micro structure and element valence states. The dominant valence states of carbon vary as carbon content increases. Carbon ion implantation remarkably enhances the current density and photocatalytic capability of TiO2 thin films. The optimized implanting content is 9.83×1017 ion/cm2, which gives rise to a 150% increased photocurrent and degradation rate.