69‐2: Invited Paper: Improved ZnO based materials for to‐date flat panel displays (original) (raw)
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34.2: Invited Paper: ZnO based transparent conductive oxides for to‐date flat panel displays
SID Symposium Digest of Technical Papers, 2019
Promising approaches to improve electrical characteristics, chemical resistance, and thermal stability of the resistivity of ZnO-based TCO thin films are investigated. The following ways were tested: a) gradient doping of ZnO grains into the synthesized TCO films by indium in order to create passivating coatings on the surface of the grains; b) preventing the oxygen diffusion into the films by suppressing the columnar structures formation; c) methods combining the above ones. It was found that in the ZnO-based TCO films deposited by magnetron sputtering at temperature above 150°C under the presence of excess zinc in the reagent flow, a decrease in the porosity of the columnar ZnO films is observed after subsequent heat treatments in air. The introducing of In, Ga, Sn metals to the composition of the ZnO films contributes to the formation of thin surface oxide sub-layers with passivation properties on the surface of the ZnO grains. The results of research clearly show that preventing the formation of a columnar structure in combination with the passivation of grain surfaces creates real prospects for expanding the areas of application of ZnO-based transparent electrodes.
ZnO Thin Film Deposition for TCO Application in Solar Cell
ZnO is a well known suitable candidate for the Transparent Conducting Oxide (TCO) layer of thin film compound solar cells. In this paper we have discussed the deposition of ZnO thin film on glass substrate by reactive DC magnetron sputtering using Oxygen as a reactive gas. Samples are prepared by varying Oxygen flow rates during the deposition process. After deposition, samples are annealed at 300 oC for 2 hours in vacuum environment. All the properties of the film are measured before and after annealing. All the samples are tested for the optical transparency, band gap and electrical resistivity before and after annealing. Band gap of film is observed 3.2 eV. XRD and SEM measurements of the samples show the variation in the crystal structure and surface morphology of the film with varying oxygen flow rate and annealing also. Around 600 nm thick ZnO film with 1.5x10-3 Ω-cm resistivity and 80% transparency without any doping is achieved.
Structural, electrical and transparent properties of ZnO thin films prepared by magnetron sputtering
Current Applied Physics, 2004
Zinc oxide (ZnO) thin films were prepared by d.c. (direct current) or r.f. (radio frequency) magnetron sputtering on glass substrates. The structural, electrical and optical properties of the films were studied. It has been found that most films produced by d.c. sputtering are not electrically conductive or have a high resistance above 10 X m, while the films produced using r.f. sputtering are significantly more conductive. The optical transmittance at 550 nm is around 80% or higher for most films. The energy band gaps of the ZnO films prepared by d.c. sputtering are smaller than the films prepared by r.f. sputtering. It is also found that the films prepared using an electrical bias have higher resistivity than those produced without bias. It has been observed by SEM that the conductive films show less porosity between the grains than the poor conductive films. Conductive ZnO films show a smaller d spacing than the non-conductive films. The results reveal that crystal microstructure and density of the ZnO films affect their conductivity.
Preparation and Characterization of ZnO:In Transparent Conductor by Low Cost Dip Coating Technique
Journal of Modern Physics, 2012
Transparent conducting oxide (TCO) based on indium doped zinc oxide films in the nano scale were successfully pre- pared using combination between dip coating and thermal decomposition process. Structural investigations confirm the polycrystalline ZnO hexagonal wurtzite phase grown along the c-axis with nano crystallite size about 10 nm. Morphol- ogy investigation shows that ZnO films consist of fine grains of average size 40 nm. This indicates that each grain con- tains several crystallites with different orientations. Cross sectional image presents good adhesion of the films with the substrate and the film thickness has been determined. Compositional analysis detects the indium content in the host ZnO matrix, the In/Zn ratio is close to the calculated concentration ratios of the precursor. The optical transmittance shows that the films are transparent in the UV and VIS-IR spectral region and interference fringes were observed to be thickness dependent. Preparation parameters were investigated and optimized such as dipping rate, number of deposi- tion cycles, precursor concentration, annealing process and In/Zn ratio. Optimization process was investigated for low resistivity, high optical spectral window transmission and easy preparation process. Dipping rate in the range 2 - 38 mm/s is the most suitable range for good film quality while dipping rate range 30 - 38 mm/s produces thicker films in lower deposition cycles. The higher dipping rate produces films with lower transparency (milky films) while the small deposition rate requires large number of deposition cycles in order to increase the thickness. Besides, the higher dipping rate reflects lower resistivity of the deposited films. Precursor molar concentration was observed to have an essential effect on the film thickness, film quality and transparency. Lower precursor concentration requires also large number of deposition cycles for thickening the films. The higher concentration results also milky films (high scattering process by powder film). Precursor concentrations in the range 0.7 - 0.9 mol/liter were found to be the optimal for better quality and for faster deposition process. The resistivity of the films has been reduced from the range 1.5 - 2.5 kW·cm to the range 100 - 400 W·cm as the molar concentration reaches the range 0.07 - 0.09 mol/liter. The resistivity of films in- creases from 330 to 1686 Ω·cm as the decomposition temperature increases from 200°C to 350°C. Annealing at 450°C process after completing the decomposition at 200°C results the lowest resistivity with annealing time in the range 1.5 - 2 h. In/Zn percentage in the range 1.5% - 5% produces the lowest electrical resistivity. The absorption edge of the de- posited films was observed to be critical affected by the preparation parameters. The band gap change was discussed through the degenerate semiconductors as well as nanostructured semiconducting materials of the energy gap confine- ment effect. Deposition of TCO based on ZnO:In was optimized depending on all deposition parameters forwide area, the lower cost and good performance TCO films.
Current Applied Physics, 2011
Ti-doped ZnO (TZO) thin films were prepared by radio frequency magnetron sputtering with a target containing 1.5 wt% TiO 2 on glass substrates at 300 C and then thermally annealed in a hydrogen ambient. The structural, electrical, and optical properties of TZO films were investigated with respect to the variation of film thickness and annealing condition. X-ray diffraction analysis exhibited that all TZO films had a (0 0 2) peak at 2q ∼34 , indicating that the films were hexagonal wurtzite structure and showed a good c-axis orientation perpendicular to the substrate. As film thickness increased from 30 to 950 nm, the crystallite size increased from 11.9 to 36.8 nm and the surface roughness increased from 0.57 to 1.78 nm. The film resistivity decreased from 3.94 Â 10 À2 to 1.06 Â 10 À3 U cm. To enhance the characteristics of TZO films for transparent conductive oxide applications, the films were subsequently annealed at temperatures ranging from 300 to 500 C in hydrogen or argon ambient for various times. The results indicated that hydrogen annealing made film resistivity decrease more than argon annealing. The resistivity of the hydrogen-annealed film monotonically decreased with increasing annealing time up to 90 min. At the optimal annealing condition (400 C, 60 min), the film resistivity decreased by 57% and the average optical transmittance in the visible wavelength range (400e700 nm) increased slightly as compared to the as-deposited films. The enhanced characteristics of the annealed TZO film are attributed to desorption of negative charged oxygen species and passivation of surface and defects at grain boundaries.
Characteristics of ZnO thin film deposited on various metal bottom electrodes
Metals and Materials International, 2003
ZnO films for electronic applications were deposited by radio-frequency (rf) sputtering onto various metal bottom electrodes (Pt/Ti, W, Ni) to investigate such structural properties as crystallinity and surface morphology. The crystallinity, surface morphology and composition of the as-deposited films were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM) and Rutherford back-scattering spectrometry (RBS), respectively. The preferred orientation and surface morphologies were strongly influenced by the type of bottom electrodes. The ZnO films with (200) texturing deposited on Pt/Ti/SiO 2 /Si showed a smoother and smaller grain size than those deposited on W and Ni. The ZnO films on Pt and W electrodes exhibited compressive residual stress.
Annealing effect on properties of transparent and conducting ZnO thin films
This work presents the effect of postdeposition annealing on the structural, electrical and optical properties of undoped ZnO (zinc oxide) thin films, prepared by radio-frequency sputtering method. Two samples, 0.17 and 0.32 µm-thick, were annealed in vacuum from room temperature to 350 °C while another 0.32 µm-thick sample was annealed in air at 300 °C for 1 h. X-ray diffraction analysis revealed that all the films had a c-axis orientation of the wurtzite structure normal to the substrate. Electrical measurements showed that the resistivity of samples annealed in vacuum decreased gradually with the increase of annealing temperature. For the 0.32 µm-thick sample, the gradual decrease of the resistivity was essentially due to a gradual increase in the mobility. On the other hand, the resistivity of the sample annealed in air increased strongly. The average transmission within the visible wavelength region for all films was higher than 80%. The band gap of samples annealed in vacuum increased whereas the band gap of the one annealed in air decreased. The main changes observed in all samples of this study were explained in terms of the effect of oxygen chemisorption and microstructural properties.
Growth and characterization of ZnO thin films prepared by electrodeposition technique
Solar Energy Materials and Solar Cells, 2006
ZnO thin films were deposited on either indium tin oxide-coated glass or copper substrate by the electrodeposition process, using zinc chloride and flowing air as precursors. The effect of pH on the structural and morphological ZnO films was studied and the optimum deposition conditions have been outlined. The kinetics of the growth of the films have been investigated. We note that the rate of deposition of ZnO in an acidic solution was larger than in a basic solution. The structure of the films was studied using X-ray diffractometry (XRD) and transmission electron microscopy (TEM). The surface morphology and thickness of the films were determined using scanning electron microscopy. The X-ray diffraction analysis shows that the films are polycrystalline with hexagonal crystal structure (zincite) at pH 4. The optical transmittance of ZnO decreases with varying film thickness. The optical energy bandgap was found to be 3.26 eV.