Molybdenum-doped ZnO Research Articles

Molybdenum-Doped ZnO Thin Films Obtained by Spray Pyrolysis.

A batch of ZnO thin films, pure and doped with molybdenum (up to 2 mol %), were prepared using the spray pyrolysis technique on glass and silicon substrates. The effect of molybdenum concentration on the morphology, structure and optical properties of the films was investigated. X-ray diffraction (XRD) results show a wurtzite polycrystalline crystal structure. The average crystallite size increases from 30 to 80 nm with increasing molybdenum content. Scanning electron microscopy (SEM) images demonstrate a smooth and homogeneous surface with densely spaced nanocrystalline grains. The number of nuclei increases, growing over the entire surface of the substrate with uniform grains, when the molybdenum concentration is increased to 2 mol %. The estimated root mean square (RMS) roughness values for the undoped and doped with 1 mol % and 2 mol % of ZnO thin films, defined by atomic force microscopy (AFM), are 6.12, 23.54 and 23.83 nm, respectively. The increase in Mo concentration contributes to the increase in film transmittance.

Precipitation of Molybdenum Oxides in Supersaturated Zinc Oxide Thin Films

Zinc oxide thin films saturated with molybdenum were prepared by RF magnetron sputtering process using zinc oxide and molybdenum targets for the co-sputtering. The sputtering power for zinc oxide was kept constant while that for molybdenum was varied from 0 watt to 35 watt. We found that the molybdenum-doped zinc oxide thin film change their color from transparent to grayish color as molybdenum sputtering power increases. The color change of the zinc oxide film suggests that the molybdenum changes its valance state as the molybdenum sputtering power was varied.A surprising finding about the study is the electrical conductivity increases and then decreases with molybdenum sputtering power. The increase of electrical conductivity should be attributed to the increase of donor concentration as more molybdenum atoms are incorporated. The decrease of conductivity, on the other hand, is not so well reported. Hall measurement study shows that the conductivity decrease is caused by decreased electron concentration. However, the electron mobility increases steadily with increased molybdenum sputtering power even though the electron concentration decreases. This is an indication that the electrical conduction no longer occurs through the molybdenum-doped ZnO grains.We propose that the conduction changes from grains to grain boundaries as molybdenum sputtering power increases. It means molybdenum is precipitated at the grain boundaries and forms conducting channels besides zinc oxide grains. The high mobility conduction channel is desired for devices using electron transport layers in their structures. The electrochemical solar cells are one of the devices that may benefit from the finding of molybdenum-doped oxide. We would like to present the valance change of molybdenum along with the conduction behavior, and would also like to predict the band alignment between zinc oxide and molybdenum oxide in the molybdenum-doped zinc oxide thin films. X-ray diffraction, UV-vis spectrophotometry, and x-ray photoelectron spectroscopy will be presented to show the conclusion that the electron mobility increase was attributed to the grain boundary conduction.

Precipitation of Molybdenum Oxides in Supersaturated Zinc Oxide Thin Films

Zinc oxide thin films saturated with molybdenum were prepared by RF magnetron sputtering process. A surprising finding about the study is the electrical conductivity increases and then decreases with molybdenum sputtering power. Hall measurement study shows that the conductivity decrease is caused by decreased electron concentration. However, the electron mobility increases steadily with increased molybdenum sputtering power in the same range even though the molybdenum incorporation still increases. This is an indication that the electrical conduction no longer occurs through the molybdenum-doped ZnO grains. We conclude that the conduction changes from grains to grain boundaries as molybdenum sputtering power increases. It means molybdenum is precipitated at the grain boundaries and forms conducting channels besides zinc oxide grains. The high mobility conduction channel might be desired for devices using electron transport layers in their structures.

P‐18: Nitrogen‐Doped Amorphous InGaZnO Thin Film Transistors Capped with Molybdenum‐Doped ZnO Ultraviolet‐Shield Layers

Nitrogen‐doped amorphous InGaZnO (a‐IGZO:N) and Molybdenum‐doped ZnO (MZO) were combined to prepare more stable thin film transistors (TFTs). The superior positive bias stress, negative bias stress, and negative bias illumination stress stabilities were observed for the a‐IGZO:N TFTs capped with MZO films, which might be due to the channel‐layer improvement by the nitrogen‐doping, the shield of ultraviolet‐lights by the MZO, and the good interface between the a‐IGZO:N and MZO.

The effect of hydrogen annealing on the molybdenum doped ZnO thin film

The electrical characteristics of hydrogen annealing on the molybdenum doped ZnO (MZO) thin film were discussed in the paper. The MZO film was deposited by an radio frequency sputtering, then it was annealed in hydrogen with a microwave plasma chemical vapor deposition system. The resistivity of MZO was decreased from 1.1 × 10−2 to 9.5 × 10−3 Ω cm after the hydrogen annealing. Improvements of the electrical properties are both due to the defects repairing through annealing and hydrogen doping effects of the MZO thin film. The higher temperature annealed MZO film shows slightly lower transmittance which is due to the higher carrier concentration.

EFFECT OF MOLYBDENUM DOPING AND ANNEALING ON PHOTOLUMINESCENCE OF SPUTTERING-DERIVED ZINC OXIDE FILMS

The molybdenum-doped ZnO (MZO) films were deposited on quartz substrates by radio frequency magnetron sputtering. All films have a polycrystalline hexagonal wurtzite structure. Mo doping influences the grain size of the MZO films and leads to a compressive stress in the films. The valence of Mo in the MZO films is hexavalence. Mo doping enhances the emissions at 380 and 412 nm. Annealing significantly influences the photoluminescence (PL) spectra of the MZO films. The PL spectral intensity of the annealed films is much higher than that of the unannealed films. The emissions at 400 and 525 nm enhanced dramatically with the rising of annealing temperature while the emissions at 380 and 412 nm became weak or disappeared. Mo doping is beneficial for the enhancement of the emissions at 400 and 525 nm of the annealed MZO films. The origins of these emissions were discussed in detail.

水热法制备钼掺杂ZnO纳米结构及其光学特性研究

Different contents of molybdenum-doped ZnO were prepared by hydrothermal method,using Zn(NO 3) 2 ·6H 2 O and NaOH as precursors,CTAB,SDS,PVP-K30,PEG400,EDTA as additive.SEM images show that various morphologies of molybdenum doped ZnO can be obtained by changing the types of additives.XRD results indicate that the doped ZnO were wurtzite structure.With the increasing of the molybdenum concentration,the diffraction peak intensity are significantly enhanced and the crystalline quality is improved.There are violet emission peak at 385 nm and green emitting at 572 nm in the PL spectra of ZnO ∶ Mo.The luminous intensity varies with the molybdenum concentration.

The properties of transparent conducting molybdenum-doped ZnO films grown by radio frequency magnetron sputtering

Transparent conducting molybdenum-doped zinc oxide films are prepared by radio frequency (RF) magnetron sputtering at ambient temperature. The MoO3 content in the target varies from 0 to 5 wt%, and each film is polycrystalline with a hexagonal structure and a preferred orientation along the c axis. The resistivity first decreases and then increases with the increase in MoO3 content. The lowest resistivity achieved is 9.2×10−4 Ω·cm, with a high Hall mobility of 30 cm2·V−1·s1 and a carrier concentration of 2.3×1020cm−3 at an MoO3 content of 2 wt%. The average transmittance in the visible range is reduced from 91% to 80% with the increase in the MoO3 content in the target.

Improvement of electrical and optical properties of molybdenum doped zinc oxide films by introducing hydrogen

Doped ZnO films are promising candidates as a front electrode in silicon film solar cells. In present work, we report on efforts to obtain highly conductive and transparent hydrogen and molybdenum co-doped ZnO (HMZO) films prepared by pulsed direct current (DC) magnetron sputtering. Investigations were made to see the effect of hydrogen (H2) flow rate on structural, electrical and optical properties. The results indicate that H2 flow rate has a considerable influence on the transparent conductive properties of molybdenum doped ZnO (MZO) films. A reduced resistivity of 69.2% and a broadening optical band gap of 5.7% were obtained with the optimal H2 flow rate of 5sccm. The average transmittance of more than 86% in the range of 400–1100nm was obtained with the optimal H2 flow rate. Crater-like surface morphology with root-mean-square (RMS) roughness of 46.5nm was also obtained after etching by diluted hydrochloric acid (HCl). Such a co-doping growing method present here may be useful for wide spectra absorption thin film solar cells.

Microstructural, Optical and Electrical Properties of Molybdenum Doped ZnO Films Deposited by Magnetron Sputtering

Microstructural, Optical and Electrical Properties of Molybdenum Doped ZnO Films Deposited by Magnetron Sputtering

Investigation of Molybdenum Doped ZnO Thin Films Prepared by Spray Pyrolysis Technique

Molybdenum doped zinc oxide thin films were deposited on the Corning glass substrates pre-heated to 400°C by spray pyrolysis technique. The effect of molybdenum doping concentration (0–2 at.%) on the structural and optical properties of zinc oxide thin films was studied. X-ray diffraction analysis confirmed that the molybdenum doped ZnO films belong to the hexagonal crystal structure of ZnO. Atomic force microscopic studies revealed the effect of molybdenum doping on the surface morphology of these films. The 1 at.% Mo doped ZnO exhibited highest average transmittance of ∼87% in the visible region (400–800 nm). Optical bandgap energy of the ZnO and Mo doped ZnO films lies in the range of 3.28–3.33 eV. Annealing of the high resistive ZnO and Mo doped ZnO films at 400°C in vacuum for 60 min improved their resistivity. The minimum resistivity of 4.7 × 10−2 Ω cm and the maximum carrier concentration of 1.27 × 1019 cm−3 were achieved for 1 at.% Mo doped ZnO films.

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.

Molybdenum-Doped Zinc Oxide Electrodes for Organic Light-Emitting Devices

The properties of molybdenum-doped ZnO (MZO) films deposited by radio-frequency (rf) magnetron sputtering and organic light-emitting devices (OLEDs) using an MZO film as an anode were investigated. A transparent conducting MZO film with high transparency and relatively low resistivity was prepared by rf magnetron sputtering at room temperature. The structural, electrical, and optical properties of the films deposited under different Ar pressures were investigated. X-ray diffraction patterns showed that the nature of the films is polycrystalline with a hexagonal structure and a preferred orientation along the c axis. Thus, MZO films may be a potential material for OLEDs.

Terahertz transmission properties of transparent conducting molybdenum-doped ZnO films

With direct current reactive magnetron sputtering method，transparent conducting molybdenum-doped ZnO （ZMO） thin films with different carrier concentration on glass substrate were fabricated by monitoring oxygen partial pressure. The dielectric responses of the ZMO 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 classic Drude model. Our results reveal that，by adjusting the carrier concentration of ZMO film，the conducting ZMO film can serve as broadband antireflection coatings for substrates and optics in terahertz frequency range.