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.     

Effects of working pressure on morphology,structural, electrical and optical properties of a-InGaZnO thin films

Amorphous In–Ga–Zn–O (a-IGZO) thin films (～200 nm thickness) were deposited by radio-frequency (RF) magnetron sputtering on silicon and glass substrates at various working pressures (0.67–2.67 Pa) and a fixed oxygen-to-argon gas-flow ratio (O₂/Ar = 5%). The transparency of all of the films was more than 85% in the visible range. With increased working pressure, the surface morphology of the films, as observed under atomic force microscopy (AFM), became rough; the optical band gap, estimated by Tauc plot, increased, and the mobility and carrier concentrations, according to Hall measurement, decreased and increased, respectively. The resistivity of the films initially decreased (up to 2.00 Pa working pressure) and then increased (at 2.67 Pa). It is suggested that the electrical property changes were affected by the role of the oxygen vacancies, whether as effective donors or as scattering centers.     

Optical and electrical properties of aluminum-doped zinc oxide nanoparticles

Aluminum-doped zinc oxide nanopowders were prepared using a surfactant assisted complex sol–gel method, and were characterized using inductively coupled plasma, X-ray diffraction, scanning electron microscopy/energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and UV–Vis spectroscopy. Al was effectively doped into the ZnO matrix with concentrations up to 6.00 atomic ratio percents (at.%). X-ray diffraction results revealed that all of the nanoparticles had a pure hexagonal wurtzite structure free of any impurities when annealing temperature was below 1273 K. The optical band gap of the nanopowders, which was affected by the Al-doping concentration, reached a maximum of 3.43 eV when ZnO was doped with 4.00 at.% Al. The effect of post-annealing temperature and vacuum conditions on the resistivities of the Al-doped ZnO nanoparticles was also investigated. And the lowest volume resistivity (1.2 Ω cm) was achieved by annealing the Al-doped ZnO nanoparticles in a vacuum at 1173 K for 2 h.     

Study on the structural, electrical, and optical properties of aluminum-doped zinc oxide films by direct current pulse reactive magnetron sputtering

A series of polycrystalline aluminum-doped zinc oxide (AZO) films were deposited on glass substrates by direct current pulse reactive magnetron sputtering at substrate temperatures (T_s) ranging from 210 °C to 290 °C. The effect of T_s on the crystalline structure, electrical, and optical properties of the as-deposited AZO films was systematically investigated by X-ray diffractometry, four-point probe measurements, and spectrophotometry. After 3 h growth, the as-deposited AZO films had no obvious (002) c-axis preferential orientation resulting from the transition of growth mode from (002) vertical growth to (103) lateral growth. The film resistivity drastically decreased when T_s was varied from 210 °C to 270 °C indicating that strong (002) preferential orientation did not ensure low resistivity. The film resistivity was, to some extent, related to the free carrier concentration and surface morphology of the film, rather than by the full width at half maximum or the integrated intensity ratio of the AZO-(002) and (103) diffraction peaks. The blue and red shifts of the T_s-related film optical absorption edge can be explained by the Burstein-Moss effect. However, the average film optical transmissivity that was independent of T_s was over 85% in the visible light region.     

Influence of annealing temperature on structural,electrical and optical properties of undoped zinc oxide thin films

The undoped zinc oxide thin films were grown on quartz substrate at a substrate temperature of 750 °C by radio frequency magnetron sputtering and post annealed at different temperatures (600–800 °C) for a period of 30 min. The influence of annealing temperature on the structure, electrical and optical properties of undoped ZnO thin films was investigated by X-ray diffraction, Hall-effect, photoluminescence and optical transmission measurements. Results indicated that the electrical properties of the thin films were extremely sensitive to the annealing temperature and the conduction type could be changed dramatically from n-type to p-type, and finally changed to weak p-type when the temperature increased from 600 to 800 °C. Electrical and photoluminescence results indicate that native defects, such as oxygen and zinc vacancies, could play an important role in determining the conductivity of these nominally undoped ZnO thin films. The conversion of the conduction type was attributed to the competition between Zn vacancy acceptor and oxygen vacancy and interstitial Zn donors. At an intermediate annealing temperature of 750 °C, the film behaves the best p-type characteristic, which has the lowest resistivity of 12 Ωcm, hall mobility of 2.0 cm²/V s and carrier concentration of 1.5 × 10¹⁷ cm^?3. The photoluminescence results indicated that the Zn vacancy might be responsible for the intrinsic better p-type characteristic in ZnO thin films.     

Effects of post-rapid thermal annealing on structural, electrical and optical properties of hydrogenated aluminum doped zinc oxide thin films

In this study, hydrogenated aluminum doped zinc oxide (HAZO) thin films were prepared by DC magnetron sputtering in different H₂/(Ar+H₂) volume ratio atmosphere. The effects of post-rapid thermal annealing (RTA) in Ar+8 % H₂ atmosphere on the structural, optical, and electrical properties of the thin films were investigated systematically. Results showed that the RTA treatment effectively improved the electrical conductivity of the HAZO thin films with small hydrogen content, due to the increase of the Hall mobility and the carrier concentration. The lowest resistivity of the HAZO thin film deposited in 8 % H₂ ratio atmosphere reached 6.3 × 10^?4 Ω cm after RTA. The improved electrical properties of the RTA-treated HAZO films were ascribed to the activation of Al dopants, the increase of oxygen vacancies and the desorption of negative charged oxygen species at the grain. These results implied that RTA process might be useful to fabricate high quality HAZO films with a low thermal budget.     

The properties of aluminum-doped zinc oxide thin films prepared by rf-magnetron sputtering from nanopowder targets

Aluminum-doped zinc oxide (ZnO:Al) films were deposited onto glass substrates by rf-magnetron sputtering at ambient temperature using, for the first time, doped nanocrystalline powder synthesized by the sol–gel method. The effects of aluminum on structural, electrical, morphological and optical properties were investigated. The films showed a hexagonal wurtzite structure and high preferential orientation in the (002) crystallographic direction. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to study the films morphology. The obtained samples have a typical columnar structure and a very smooth surface. The optical transmittance spectra showed transmittance higher than 90% within the visible wavelength region. A minimum resistivity of 5.436 · 10^− 5 Ω cm at room temperature was obtained for the 3.0 at.% Al-doped film.     

Morphological, optical and electrical properties of samarium oxide thin films

We present here results on samarium oxide thin films, obtained by pulsed laser deposition and by radio frequency assisted pulsed laser deposition. Three different substrate types were used: silicon, platinum covered silicon and titanium covered silicon. The influence of the deposition parameters (oxygen pressure and laser fluence) on the structure and morphology of the thin films was studied. The substrate-thin film interface zone was investigated; the optical and electrical properties (the losses, dielectric constant and leakage currents) were also determined.     

Effects of hydrogen annealing on the structural, optical and electrical properties of indium-doped zinc oxide films

Indium-doped zinc oxide (IZO) films were fabricated by radio-frequency magnetron sputtering. The effects of hydrogen annealing on the structural, optical and electrical properties of the IZO films were investigated. The hydrogen annealing may deteriorate the crystallinity of the films. The surfaces of the films would be damaged when the annealing temperature was higher than 350 °C. After the annealing, the surface roughness of the films would decrease, and high transparency of 80–90% in the visible and near-infrared wavelength would be kept. Meanwhile, the resistivity decreased from 1.25 × 10⁻³ Ωcm of the deposited films to 6.70 × 10⁻⁴ Ωcm of the annealed films. The work function of the IZO films may be modulated between 4.6 and 4.98 eV by varying the hydrogen annealing temperature and duration.     

Structural,morphological, optical and electrical properties of spray deposited zinc doped copper oxide thin films

Nanostructured spray deposited zinc (Zn) doped copper oxide (CuO) thin films were characterized by employing X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX), atomic force microscopy (AFM) and ultraviolet–visible–near infrared (UV–Vis–NIR) spectroscopy. XRD patterns of CuO and Zn doped CuO thin films indicated monoclinic structure with the preferred orientation along \(\left( {\bar 111} \right)\) plane. Maximum value of crystallite size is found about 28.24 nm for 5 at% Zn doped CuO thin film. In FESEM images, nanoparticles were observed around the nucleation center. EDX analysis confirms the presence of all component elements in CuO and Zn doped CuO thin films. Analysis by AFM of CuO and Zn doped CuO thin films figured out decrease of surface roughness due to Zn doping. UV–Vis–NIR spectroscopy showed that CuO and Zn doped CuO thin films are highly transparent in the NIR region. Optical band gap of CuO thin films decreased with substrate temperature and that of Zn doped CuO thin films increased with Zn concentration. Refractive index of CuO and Zn doped CuO thin films raised with photon wavelength and became constant in the NIR region. 5 at% Zn doped CuO thin film showed the highest optical conductivity and the lowest electrical resistivity at room temperature.     

The influence of substrate temperature on the properties of aluminum-doped zinc oxide thin films deposited by DC magnetron sputtering

Transparent, conducting, aluminum-doped zinc oxide (AZO) thin films were deposited on Corning 1737 glass by a DC magnetron sputter. The structural, electrical, and optical properties of the films, deposited using various substrate temperatures, were investigated. The AZO thin films were fabricated with an AZO ceramic target (Al₂O₃:2 wt%). The obtained films were polycrystalline with a hexagonal wurtzite structure and preferentially oriented in the (002) crystallographic direction. The lowest resistivity was 6.0 × 10⁻⁴Ω cm, with a carrier concentration of 2.7 × 10²⁰ cm⁻³ and a Hall mobility of 20.4 cm²/Vs. The average transmittance in the visible range was above 90%.     

Effects of air annealing on the optical, electrical, and structural properties of indium-tin oxide thin films

The effects of air annealing on the optical, electrical, and structural properties of indium-tin oxide thin films were investigated using spectroscopic ellipsometry in the UV-visible range, reflectance-transmittance spectra at normal incidence in the infrared range, electrical resistivity measurements, and X-ray diffraction. It was found that annealing at 300 °C produces an overall shift to lower photon energies of the optical constant spectra, which is related to the increase in electrical resistivity. The electrical measurements performed in the 25-300 K range show a metallic behavior with large residual resistivity, quantity that increases with annealing temperature and is closely related with the change in the relative intensity of the main diffraction peaks. Also it is shown that under certain conditions of film deposition onto indium-tin oxide, some of its properties can change in a similar way as in air-annealing processing.     

Investigation of annealing-treatment on structural and optical properties of sol-gel-derived zinc oxide thin films

The transparent ZnO thin films were prepared on Si(100) substrates by the sol-gel method. The structural and optical properties of ZnO thin films, submitted to an annealing treatment in the 400–700°C ranges are studied by X-ray diffraction (XRD) and UV-visible spectroscopic ellipsometry (SE). XRD measurements show that all the films are crystallized in the hexagonal wurtzite phase and present a random orientation. Three prominent peaks, corresponding to the (100) phase (2θ ≈ 31.8°), (002) phase (2θ ≈ 34.5°), and (110) phase (2θ ≈ 36.3°) appear on the diffractograms. The crystallite size increases with increasing annealing temperature. These modifications influence the optical properties. The optical constants and thickness of the films have been determined by analysing the SE spectra. The optical bandgap has been determined from the extinction coefficient. We found that the refractive index and the extinction coefficient increase with increasing annealing temperature. The optical bandgap energy decreases with increasing annealing temperature. These mean that the optical quality of ZnO films is improved by annealing.     

Post-annealing properties of aluminum-doped zinc oxide films fabricated by ion beam co-sputtering

Aluminum-doped zinc oxide (AZO) films were fabricated by using the ion beam sputter deposition (IBSD) method with dual metallic targets, Al and Zn, co-sputtered by argon ion beam in an oxygen ambient. Structural and electrical properties of AZO films before and after annealing were ex situ investigated by the X-ray diffractometer and Hall measurement with the Van der Pauw method, respectively. The intense (002) diffraction peak and simultaneously the low resistivity were observed in the as-deposited film. The resistivity of the film after 400 °C post-anneal increased more than two orders of magnitude than that of the as-deposited film resulting from the decrease of the donor concentration and mobility in the AZO film. The residual stress was derived from the results of the XRD patterns. Finally, it was found that the film resistivity increased as the annealing temperature increased and a corresponding shift of the energy band gap was observed.     

The electrical and optical properties of indium zinc tin oxide thin films with different Sn/Zn ratio

Indium zinc tin oxide (IZTO) thin films with two different chemical compositions, i.e. IZTO15 and IZTO25, where In content was fixed at 60 at.% and Sn content was 15 and 25 at.%, respectively, were deposited onto alkaline-free glass substrate at temperature from 37 °C to 600 °C. The deposition process was carried out in argon using an RF magnetron sputter. After deposition, the films were annealed in argon atmosphere at 450 °C for 30 min. The effect of substrate temperature and annealing treatment was investigated, and the minimum resistivity value of 3.44 × 10^− 4Ω.cm was obtained from the film deposited at 400 °C using IZTO25 target followed by rapid thermal annealing at 450 °C for 30 min. The average optical transmittance was kept fairly high over 80%. It was proven that both substrate temperature and thermal annealing were important parameters in lowering the electrical resistivity without deteriorating optical properties.     

Investigation on structural, electrical and optical properties of tungsten-doped tin oxide thin films

Tungsten-doped tin oxide (SnO₂:W) transparent conductive films were prepared on quartz substrates by pulsed plasma deposition method with a post-annealing. The structure, chemical states, electrical and optical properties of the films have been investigated with tungsten-doping content and annealing temperature. The lowest resistivity of 6.67 × 10^− 4 Ω cm was obtained, with carrier mobility of 65 cm² V^− 1 s^− 1 and carrier concentration of 1.44 × 10²⁰ cm^− 3 in 3 wt.% tungsten-doping films annealed at 800 °C in air. The average optical transmittance achieves 86% in the visible region, and approximately 85% in near-infrared region, with the optical band gap ranging from 4.05 eV to 4.22 eV.     

Electrical,optical, and topographical properties of RF magnetron sputtered aluminum-doped zinc oxide (AZO) thin films complemented by first-principles calculations

The fabrication of an efficient electron transport layer (ETL) with high conductivity and transparency is of significant interest. Aluminum doped zinc oxide (AZO) is an established ETL candidate due to its excellent conductivity and transparency, especially in the visible–near infrared (Vis–NIR) spectral range. Herein, we attempt to understand AZO properties by both experimental and computational approaches, as far as these methodologies permit. As part of our approach, we have deposited AZO thin films using radio frequency sputtering technique under two different sets of conditions, batch-I (150, 175, and 200 W; 0.2 mTorr; 20 min) and batch-II (70 W; 2 mTorr; 75 min). And, we have studied the structural, morphological, topographical, electrical, and optical properties of thus deposited films. The results are complemented by first-principles calculations based on the density functional theory (DFT) performed over a 2?×?2?×?2 and 3?×?2?×?2 supercell of wurtzite ZnO, to assess the effect of one aluminum atom substitution on the structural, electronic, and optical properties of the solid. We could discuss, thus, obtained computational results by comparing with the experimental measurements through a reliable construction of aluminum doping percentage models (3.12 and 2.08 at.%).     

On the structural and electrical characteristics of zinc oxide thin films

ZnO thin films with thickness d = 100 nm were deposited by radio frequency magnetron sputtering onto glass substrate from different targets. The structural analyses of the films indicate they are polycrystalline and have a wurtzite (hexagonal) structure. Crystallites are preferentially oriented with (002) plane parallel to the substrate surface and the samples have low values for surface roughness, between 1.7 nm and 2.7 nm. The mechanism of electrical conduction in the studied films is strongly influenced by this polycrystalline structure and we used Van der Pauw method to analyze these properties. Electrical studies indicate that the ZnO thin films are n-type. For the cooling process, thermal activation energy of electrical conduction of the samples can vary from 1.22 eV to 1.07 eV (for the ZnO layer obtained from for metallic Zn target) and from 0.90 eV to 0.63 eV (for the ZnO layer obtained from ZnO target), respectively. The influence of deposition arrangement and oxidation conditions on the structural and electrical properties of the ZnO films was investigated in detail.     

Growth and optical properties of aluminum-doped zinc oxide nanostructures on flexible substrates in flexible electronics

Undoped ZnO nanowire arrays and Al-doped ZnO nanostructures with nanowires and nanosheets were successfully synthesized on a polyethylene terephthalate substrate using the rapid hydrothermal synthesis. These undoped ZnO nanowire arrays showed close alignment with highly c-axis oriented and well-defined hexagonal facets (001). The coexistence of the nanowires and nanosheets was observed during the introduction of Al ions. The number of nanosheets increased due to the Al doping concentration and the lack of surface energy. The diameter of the nanosheets and the length of nanowire arrays also increased as a function of the growth time. Room-temperature photoluminescence spectra show that the ZnO:Al nanostructures on the ZnO seeded polyethylene terephthalate substrate yield low level of the defect density compared to the ZnO seeded glass substrate to remove post annealing process.