Co-doped Zinc Oxide Thin Films Research Articles

Influence of lithium substitution on the orange emission in manganese doped ZnO thin films

Lithium (Li) and Manganese (Mn) co-doped zinc oxide (ZnO) thin films have been deposited on glass substrates by sol–gel spin-coating technique. The influence of the defect states on the orange emission has been studied by altering the defect chemistry through appropriate Li substitution. The results of the defect related fluorescence in the blue and green regions have been combined to elucidate comprehensively the defect-mediated energy transfer mechanism of orange emission in Li and Mn co-doped ZnO thin films.

Doped zinc oxide window layers for dye sensitized solar cells

The present paper reports the fabrication of dye sensitized solar cell (DSSC), where boron doped ZnO (BZO) and aluminum-boron co-doped ZnO (AZB) thin films were used as front window electrodes. The highly crystalline zinc oxide (ZnO) nanoparticles (NPs) synthesized by the sol-gel route were used as host material for the dye. The efficiencies of the DSSCs formed using the BZO and AZB as window layers were obtained to be 1.56 and 1.84%, respectively. The enhanced efficiency in the case of an AZB window layer based DSSC is attributed to the increase in conductivity induced by co-doping of Al and B and an increase in the number of conducting pathways between the window layer and NPs provided by the nanorods. This facilitates a new approach in the window layer (doped ZnO) for DSSC application.

Preparation and Optical Properties of Gallium-Titanium Codoped Zinc Oxide Transparent Conductive Films for Solar Cells

Transparent conducting gallium-titanium codoped zinc oxide thin films were grown onto glass substrates with magnetron sputtering technique in ambient argon gas, and the influence of argon pressure on optical properties of the films were investigated. The refractive indexes of the films were calculated. It is found that the refractive index tends to increase with increasing the photon energy. Meanwhile, the dispersion behavior of the refractive index was analyzed in terms of the single-oscillator model and the oscillator parameters were obtained. Furthermore, the optical energy gaps were evaluated by single-oscillator model and Tauc’s relation, respectively. The values of optical energy gap estimated from single-oscillator model are in agreement with those determined from Tauc’s relation.

Effect of working pressure on the structural, optical and electrical properties of titanium-gallium co-doped zinc oxide thin films

The transparent conducting titanium-gallium co-doped zinc oxide (TGZO) thin films were grown on glass substrates by radio-frequency magnetron sputtering technique. The effects of working pressure on the structural, optical and electrical properties of the films were investigated. The results show that the deposited films are polycrystalline with a hexagonal wurtzite structure and highly textured along the c-axis perpendicular to the substrate. The TGZO film prepared at the working pressure of 0.4 Pa exhibits the best crystallinity, the maximal grain size, the highest transmittance, the lowest resistivity and the highest figure of merit. The optical constants of the films were calculated using the method of optical spectrum fitting. The dispersion behavior of the films was studied by the single-electronic oscillator dispersion model. The oscillator parameters and optical bandgaps were determined. The results demonstrate that the microstructure and optoelectrical properties of the TGZO films are dependent on the working pressure.

Investigation of UV photoresponse property of Al, N co-doped ZnO film

Abstract Al, N co-doped zinc oxide thin films were prepared using sol–gel assisted spin coating method with a range of nitrogen (N) doping ( x = 0, 1, 2). The deposited films were characterized through X-ray diffraction, UV–visible spectroscopy, photoluminescence spectroscopy and hall measurements to find structural, optical and electrical properties. The X-ray diffraction pattern was confirmed the existence of polycrystalline nature with wurtzite structure. The strong band emission and green emission peaks have been observed in Al, N co-doped films. The nitrogen undoped film demonstrated n-type conductivity and nitrogen doping brings p-type conductivity with maximum hole concentration of 8.111 × 10 16 cm −3 , carrier mobility of 9.965 cm 2 /V.s for higher nitrogen doped film ( x = 2). The UV photo responsivity (7.17 × 10 –5 A/W) and gain (724.36 × 10 –5 ) of photo detector has been improved by a one order of magnitude in low nitrogen doping and decay time has been reduced drastically from 58.27 s to 10.32 s. These results demonstrated that the improved responsivity and decay time by 1 at% of nitrogen doping.

Synthesis and characterization of undoped, Al and/or Ho doped ZnO thin Films

Abstract The deposition of undoped, aluminum and/or holmium doped and co-doped zinc oxide thin films on different substrates was achieved using a very simple and versatile aqueous solution method. The effect of the precursor solution concentration on the morphological and structural characteristics, as well as on the optical properties of the undoped ZnO thin films was also investigated. The AFM investigations have revealed that the morphology of the films is smooth and homogeneous. The room-temperature photoluminescence (PL) and the optical absorption (UV–vis) properties of the as-obtained undoped and doped ZnO thin films were investigated, as well. A strong UV emission (380 nm) was recorded for the undoped, aluminum and holmium doped and co-doped ZnO thin films. The band gap value obtained for the doped ZnO thin films is ranging between 3.01 eV and 3.56 eV, depending on the nature and the concentration of the dopant.

Polymer-Assisted Deposition of Co-Doped Zinc Oxide Thin Films for the Detection of Aromatic Organic Compounds

Co-doped Zinc oxide thin films are deposited onto SiO2/Si substrate by polymer-assisted deposition method. The surface morphology, structures and chemical states of the thin films are examined by scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The gas-sensing properties of the thin films upon exposure to aromatic organic compound vapors are also investigated. Co-doping is shown to be very effective in enhancing the response of ZnO thin film to aromatic organic compound.

Implementation of High Carrier Mobility in Al-N Codoped p-Type ZnO Thin Films Fabricated by Direct Current Magnetron Sputtering with ZnO:Al2O3Ceramic Target

In this study, Al-N codoped p-type zinc oxide (ZnO) thin films were deposited on Si and homo-buffer layer templates in a mixture of and gas with ceramic ZnO:(2 wt% ) as a sputtering target using DC- magnetron sputtering. X-ray diffraction spectra of two-theta diffraction showed that all films have a predominant (002) peak of ZnO Wurtzite structure. As the fraction in the mixed and gases increased, field emission secondary electron microscopy revealed that the surface appearance of codoped films on Si varied from smooth to textured structure. The p-type ZnO thin films showed carrier concentration in the range of , resistivity in the range of 131.2-2.864 , and mobility in the range of respectively.

Characterization of gallium–nitrogen co-doped zinc oxide thin films prepared by RF diode sputtering

We investigated the possibility of achieving p-type zinc oxide (ZnO) by RF diode sputtering and gallium–nitrogen co-doping. ZnO:Ga:N thin films were prepared with a different N2 content in Ar/N2 working gas, ranging from 0 to 100%, and at a varying substrate temperature, from room temperature (RT) to 300 °C. A hole conduction with maximum carrier concentration of 2.6 × 1018 cm−3, mobility of 2 cm2/Vs and resistivity of 1.5 Ω cm resulted from deposition at RT with 100% N2. It arose from N incorporation and formation of NO acceptors. In the secondary ion mass spectrometry (SIMS) depth profiles of the co-doped films were observed NO/NO2 negative ions. Average transmittance (including Corning glass substrate) across the visible spectrum varied (60 ÷ 66%) with increasing nitrogen content (50 ÷ 100% N2). As the substrate temperature increased (RT – 300 °C), highly transparent (T ∼72–83%) and conductive (electron concentrations of 1017–1019 cm−3) n-type ZnO:Ga:N films were attained. Reduction of optical band gap (Eg) (∼3.13–3.08 eV) was observed for co-doped ZnO films. Atomic force microscopy (AFM) images revealed that the films grown at RT have roughness of approximately 5.3 nm while roughness of those grown at 300 °C is approximately 3.9 nm.

Effect of aluminum and indium co-doping on zinc oxide films prepared by dc magnetron sputtering

Aluminum and indium co-doped zinc oxide (AIZO) thin films were prepared by direct current (dc) magnetron sputtering on glass substrate in pure argon atmosphere. Three inches of zinc oxide ceramic with 0.5 wt.% of aluminum and indium doping was used as a target in static mode. The influence of sputtering conditions i.e. substrate–target distance, pressure and power on AIZO films was studied. The electrical resistivity and microstructure of thin films were investigated by the four point probe technique and the scanning electron microscope, respectively. The optical transmittance of AIZO films was measured by UV visible spectrophotometer in the wavelength of 300–1100 nm. Depending on the deposited conditions, highly transparent films up to 80% with low resistivities in the range of 2.6–7.9 × 10 − 4 Ω cm were achieved at room temperature. Possible mechanism in the processing which, ultimately, determines the physical properties of AIZO films will be discussed.

Physical properties of indium and fluorine codoped zinc oxide thin films deposited by chemical spray

Indium and fluorine codoped zinc oxide (ZnO:In + F) thin films were deposited on glass substrates by the chemical spray technique. The effect of the dopant concentration ratio in the starting solution, as well as the substrate temperature on the electrical, morphological, structural, and optical properties of ZnO:In + F thin films was studied. A minimum electrical resistivity, in the order of 3.4 × 10 −3 Ω cm, for as-grown films deposited at 475 °C from a starting solution containing [In]/[Zn] = 3 and [F]/[Zn] = 20 at.%, was obtained. All the films were polycrystalline, and some differences in the intensity of the peaks and preferential growth, depending on the doping ratios, were observed. The deposited ZnO:In + F thin films showed an average optical transmittance in the order of 85%, in the visible region (400–700 nm). The band gap values oscillated around 3.35 and 3.39 eV, and a shift towards higher values with the increase of the dopant concentration was observed. The surface morphology of the films was also strongly affected by the dopant concentration ratio, since a variation in both geometry and grain size was observed.

Influence of post-deposition annealing on the structural, optical and electrical properties of Li and Mg co-doped ZnO thin films deposited by sol–gel technique

Lithium (Li) and magnesium (Mg) co-doped zinc oxide (ZnO) thin films were deposited by sol–gel method using spin coating technique. The films were deposited on glass substrates and annealed at different temperatures. The effects of annealing temperature on the structural, optical and electrical properties of the deposited films were investigated using X-ray diffraction (XRD), Ultraviolet–Visible absorption spectra (UV–VIS), photoluminescence spectra (PL), X-ray photo electron spectroscopy (XPS) and Hall measurements. XRD patterns indicated that the deposited films had a polycrystalline hexagonal wurtzite structure with preferred (0 0 0 2) orientation. All films were found to exhibit a good transparency in the visible range. Analysis of the absorption edge revealed that the optical band gap energies of the films annealed at different temperatures varies between 3.49 eV and 3.69 eV. Room temperature PL spectra of the deposited films annealed at various temperatures consist of a near band edge emission and visible emission due to the electronic defects, which are related to deep level emissions, such as oxide antisite (O Zn), interstitial zinc (Zn i), interstitial oxygen (O i) and zinc vacancy (V Zn) which are generated during annealing process. The influence of annealing temperature on the chemical state of the dopants in the film was analysed by XPS spectra. Ion beam analysis (Rutherford back scattering) experiments were performed to evaluate the content of Li and Mg in the films. Hall measurements confirmed the p-type nature of the deposited films.

Structural and Optical Properties of Cobalt-Doped Zinc Oxide Thin Films Prepared By Spray Pyrolysis Technique

Undoped and Co-doped zinc oxide (CZO) thin films have been prepared by spray pyrolysis technique using solution of zinc acetate and cobalt chloride. The effect of Co dopants on structural and optical properties has been investigated. The films were found to exhibit maximum transmittance (~90%) and low absorbance. The structural properties of the deposited films were examined by x-ray diffraction (XRD). These films, deposited on glass substrates at (400? C), have a polycrystalline texture with a wurtzite hexagonal structure, and the grain size was decreased with increasing Co concentration, and no change was observed in lattice constants while the optical band gap decreased from (3.18-3.02) eV for direct allowed transition. Other parameters such as Texture Coefficient (Tc), dislocation density (?) and number of crystals (M) were also calculated .

Structural and Optical Properties of Cobalt-Doped Zinc Oxide Thin Films Prepared By Spray Pyrolysis Technique

Undoped and Co-doped zinc oxide (CZO) thin films have been prepared by spray pyrolysis technique using solution of zinc acetate and cobalt chloride. The effect of Co dopants on structural and optical properties has been investigated. The films were found to exhibit maximum transmittance (~90%) and low absorbance. The structural properties of the deposited films were examined by x-ray diffraction (XRD). These films, deposited on glass substrates at (400? C), have a polycrystalline texture with a wurtzite hexagonal structure, and the grain size was decreased with increasing Co concentration, and no change was observed in lattice constants while the optical band gap decreased from (3.18-3.02) eV for direct allowed transition. Other parameters such as Texture Coefficient (Tc), dislocation density (?) and number of crystals (M) were also calculated .

Influence of the distance between target and substrate on the properties of transparent conducting Al–Zr co-doped zinc oxide thin films

Highly transparent and conducting Al–Zr co-doped zinc oxide (ZAZO) thin films were successfully prepared on glass substrate by direct current (DC) magnetron sputtering at room temperature. The distance between target and substrate was varied from 45 to 70 mm. All the deposited films are polycrystalline with a hexagonal structure and have a preferred orientation along the c-axis perpendicular to the substrate. The crystallinity increases obviously and the electrical resistivity decreases when the distance between target and substrate decreases from 70 to 50 mm. However, as the distance decreases further, the crystallinity decreases and the electrical resistivity increases. When the distance between target and substrate is 50 mm, it is found that the lowest resistivity is 6.9 × 10−4 Ω·cm. All the deposited films show a high average transmittance of above 92% in the visible range.

Effect of Doping on the Optical and Structural Properties of ZnO Thin Films Prepared by RF Diode Sputtering

Nitrogen-doped zinc oxide thin films (ZnO:N), and aluminum-nitrogen co-doped zinc oxide thin films (ZnO:Al:N), were deposited on Corning glass substrates by RF diode sputtering. The nitrogen (N2) content in the working gas varied from 0 to 100 %. XRD patterns revealed improving of the crystalline structure and stronger expressed c-axis preferential orientation of the aluminum-nitrogen co-doped films compared to nitrogen-doped films. The estimated crystallite size varied from 140 to 8 nm, depending on the N2 content. The transmittance spectra of ZnO:N and ZnO:Al:N films were acquired over the wavelength range of 200 < λ < 1000 nm. All nitrogen-doped and Al-N2 co-doped films were colored as a result of the increase absorption near the band edge. Optical band gap (Eg) of the ZnO:N and ZnO:Al:N thin films decreases with increase of the N2 content in the working gas.

Fabrication of low-resistive p-type Al–N co-doped zinc oxide thin films by RF reactive magnetron sputtering

Abstract p-Type aluminum–nitrogen (Al–N) co-doped zinc oxide (ZnO) thin films were deposited on glass substrate at 300 °C by RF reactive magnetron sputtering using an aluminum-doped zinc oxide (2.4 wt%Al2O3) target and N2 reactive gas. In addition, the effect of N2 reactive gas on the electrical and structural properties of Al–N co-doped ZnO thin films was also investigated. It was found that p-type Al–N co-doped ZnO thin films could be obtained only when the volume ratio of N2 in the N2-containing Ar working gas exceeded 10%. p-Type Al–N co-doped ZnO thin films with a minimum resistivity of 0.141 Ω cm, a p-type carrier concentration of 5.84×1018 cm−3, and a Hall mobility of 3.68 cm2/V s were obtained in this study when the volume ratio of N2 in the working gas was 30%.

Fabrication and properties evaluation of aluminum and ruthenium co-doped zinc oxide thin films

Aluminum and ruthenium co-doped zinc oxide transparent conducting thin films were grown on polyethylene terephthalate substrate at 20 °C by RF magnetron sputtering method. The structural and physical properties of the films were investigated with respect to variation of discharge power density. The XRD and FESEM results show that the film with 3.6 W/cm 2 power density has the best crystallinity and larger pyramid-like grains, therefore the resistivity reached to lowest value of 8.6 × 10 −4 Ω cm. The low carrier mobilities of the films (3.6–8.9 cm 2 V −1 s −1) not only were limited by ionized impurity scattering since the carrier concentrations were ranged from 2.0 × 10 20 to 8.2 × 10 20 cm −3, but chemisorption of oxygen on the film surface and grain boundary has to be taken into account. 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.

Structural and Optical Properties of Co-Doped ZnO Thin Films

Received 20 August 2004; accepted 29 September 2004 Co-doped zinc oxide thin films (Zn1−xCoxO) have been deposited on c-plane sapphire substrates by dual-beam pulsed laser deposition. The films have lattice parameters similar to that of ZnO, and the lattice parameters are closely distributed. The films grew along a preferred direction, following the epitaxial relationship Zn1−xCoxO (0001)//substrate (0001). Excitonic emission was suppressedat higher Co-dopant concentration in ZnO because of increase in the distortion of host lattice and defects. When more Zn is replaced by Co, more impurity levels are developed within the bandgap, and more defect are generated. Under our experimental conditions, the bandgap of the films tends to increase with increasing dopant concentration.

Effect of oxygen partial pressure ratios on the properties of Al–N co-doped ZnO thin films

p-Type zinc oxide (ZnO) thin films with C-axis orientations were realized using the DC reactive magnetron sputtering by Al and N co-doping method. Second ion mass spectroscopy (SIMS) tests proved that both Al and N were doped in the ZnO films and the incorporation of Al facilitated the N solution into ZnO, thus promoted the formation of p-type conduction. When oxygen partial pressure ratios was 40% or 85%, the as-grown ZnO thin films showed p-type conduction, and the latter had better electrical properties. The obtained p-type ZnO films showed a resistivity of 157 Ω cm, a hole concentration of 5.59×10 17 cm −3, and a Hall mobility of 0.0711 cm 2/V s at room temperature. X-ray diffraction (XRD) patterns showed that the ZnO film prepared in 60% of oxygen partial pressure ratio had the best C-axis orientation. The as-grown ZnO films possessed transmittance of about 90% in the visible region.