Densification of In2O3:Sn multilayered films elaborated by the dip-coating sol-gel route

Indium Tin Oxide (ITO) thin films have been deposited by the Sol-Gel Dip-Coating technique, the starting solutions being prepared from chlorides. These multilayered films were crystallized by means of a classical heat treatment at temperatures ranging from 500 to 600 °C. Five stacked layers are necessary to obtain a global electrical resistivity value of 2.9×10⁻³ Ω cm, for 500 °C annealed film. The paper focuses on the study of the structure of such multilayered deposits, and on the densification process, using transmission electron microscopy, Rutherford Back-scattering Spectrometry and electrical resistivity measurements. This analysis reveals structural inhomogeneities and different crystallite growth processes as a function of annealing temperature and number of deposited layers.     

Effect of heat treatment on characteristics of nanocrystalline ZnO films by electron beam evaporation

Zinc oxide thin films have been grown on glass substrate at room temperature by electron beam evaporation and then were annealed in annealing pressure 600 mbar at different temperatures ranging from 250 to 550 °C for 30 min. Electrical, optical and structural properties of thin films such as electrical resistivity, optical transmittance, band gap and grain size have been obtained as a function of annealing temperature. X-ray diffraction has shown that the maximum intensity peak corresponds to the (002) predominant orientation for ZnO films annealed at various temperatures. The full width at half maximum, decreases after annealing treatment which proves the crystal quality improvement. Scanning electron microscopy images show that the grain size becomes larger by increasing annealing temperature and this result agrees with the X-ray diffraction analysis.     

Effect of annealing temperature on structural, electrical and optical properties of B-N codoped ZnO thin films

The B-N codoped p-type ZnO thin films have been prepared by radio frequency magnetron sputtering using a mixture of nitrogen and oxygen as sputtering gas. The effect of annealing temperature on the structural, electrical and optical properties of B-N codoped films was investigated by using X-ray diffraction, Hall-effect, photoluminescence and optical transmission measurements. Results indicated that the electrical properties of the 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 in a range from 600 °C to 800 °C. The B-N codoped p-type ZnO film with good structural, electrical and optical properties can be obtained at an intermediate annealing temperature region (e.g., 650 °C). The codoped p-type ZnO had the lowest resistivity of 2.3 Ω cm, Hall mobility of 11 cm²/Vs and carrier concentration of 1.2 × 10¹⁷ cm^− 3.     

Effects of vapor annealing on the properties of the ZnO films prepared by spray pyrolysis

Zinc oxide (ZnO) films were deposited on (0 0 0 1) sapphire substrates from a solution containing zinc acetate. The films were deposited in a vertical type hot wall reactor by the pyrolysis of an aerosol produced by an ultrasonic generator. To increase the resistivity of the films, copper doping and annealing in an ambient of water vapor (vapor annealing) were carried out. The resistivity of a 0.5 wt % copper doped ZnO film was around 24 cm. The vapor annealing resulted in a 10⁷-fold increase in the resistivity. After annealing, the crystallinity of the films was improved, as determined by X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM). All the films annealed at 600°C for 2 h exhibited a strong (0 0 2) orientation with a smooth surface The crystallinity, surface morphology, composition and electrical properties of the as-deposited and vapor-annealed films were investigated.     

Annealing effect of ZnO/Au/ZnO transparent conductive films

Au intermediate ZnO (ZAZ) thin films were prepared by radio frequency and direct current magnetron sputtering on glass substrates and then vacuum annealed. The thickness of each layer of the ZAZ films was set at 50 nm, 3 nm, and 47 nm, respectively. The structural, electrical, and optical properties of ZAZ films were investigated with respect to the variation of annealing temperature.As-deposited AZO films showed X-ray diffraction peaks corresponding to ZnO (002) and Au (111) planes and those peak intensities increased with post-deposition vacuum annealing. The optical and electrical properties of the films were strongly influenced by post-deposition annealing. Although the optical transmittance of the films deteriorated with an Au interlayer, as-deposited ZAZ films showed a low resistivity of 2.0 × 10⁻⁴ Ω cm, and the films annealed at 300 °C had a lower resistivity of 9.8 × 10⁻⁵ Ω cm. The work function of the films increased with annealing temperature, and the films annealed at 300 °C had a higher work function of 4.1 eV than the films annealed at 150 °C. The experimental results indicate that vacuum-annealed ZAZ films are attractive candidates for use as transparent electrodes in large area electronic applications such as solar cells and large area displays.     

Structural and electrical properties of evaporated Cr-Ni films as a function of gas pressure

Electrical measurements of 60 Cr-40 Ni films evaporated in UHV or at a definite partial pressure of N₂ and He showed that all continuous films have a positive temperature coefficient of resistivity (TCR). The electron diffraction pattern of these films could be indexed tetragonal (c/a=1.36; a=5.2 Å). Chromium was precipitated after annealing the films for 6 h at 300 °C in UHV.On evaporating Cr-Ni films at an oxygen partial pressure of 1 x 10^-6 torr the TCR became negative. The films had a structure corresponding to a distorted b.c.c. Cr lattice, which did not change even after annealing for several hours at 300 °C. This is given as a reason for the better electrical stability of these films. Possible explanations for the negative TCR of films evaporated in the presence of oxygen are also discussed.     

Rapid thermal-plasma annealing of ZnO:Al films for silicon thin-film solar cells

Rapid thermal annealing of sputter-deposited ZnO and Al-doped ZnO (AZO) films with and without an amorphous silicon (a-Si) capping layer was investigated using a radio-frequency (rf) argon thermal plasma jet at atmospheric pressure. The resistivity of bare ZnO films on glass decreased drastically from 10⁶ to 10³ Ω·cm at maximum surface temperatures T_max above 650 °C, whereas the resistivity increased from 10^− 4 to 10^− 3-10^− 2 Ω·cm for bare AZO films. On the other hand, the resistivity of AZO films with a 30-nm-thick a-Si capping layer remained below 10^− 4 Ω·cm, even after TPJ annealing at a T_max of 825 °C. X-ray diffraction and X-ray photoemission electron studies revealed that the film crystallization of both AZO and a-Si layers was promoted without the formation of an intermixing layer. Additionally, the crystallization of phosphorous- and boron-doped a-Si layers at the sample surface was promoted, compared to that of intrinsic a-Si under identical plasma annealing conditions. The role of the a-Si capping layer on sputter-deposited AZO and ZnO films during TPJ annealing is demonstrated. The effects of the mixing of phosphorous and boron impurities in a-Si:H during TPJ annealing of flat and textured AZOs are also discussed.     

Activation of p-type conduction in ZnO:N films by annealing in atomic oxygen

ZnO:N epitaxial films have been grown by reactive magnetron sputtering. The effect of annealing in atomic oxygen on the structural and electrical properties of the ZnO:N films has been studied by X-ray diffraction, atomic force microscopy, Hall effect measurements, and X-ray photoelectron spectroscopy. By annealing at temperatures from 500 to 700°C, we have obtained p-type ZnO:N films with a resistivity of ～57 Ω cm, hole mobility of ～2.7 cm²/(V s), and hole concentration of ～6.8 × 10¹⁷ cm^?3. X-ray photoelectron spectroscopy results suggest that the p-type conductivity of the films is due to a decrease in the concentration of (N₂)_O and V _O donors.     

Composition, surface morphology and electrical characteristics of Al2O3-TiO2 nanolaminates and AlTiO films on silicon

We propose and demonstrate Metal-Oxide-Semiconductor structures comprising Al₂O₃-TiO₂ nanolaminate and AlTiO films. Composition, structural and electrical characteristics were studied in detail and compared to TiO₂ thin film-based structures. All dielectric films were evaporated using an electron beam gun (EBG) system on unheated p-Si substrate without adding O₂. MOS structures were investigated in detail before and after annealing at up to 950 °C in O₂ and N₂ + O₂ environments. The nanolaminate films remain in an amorphous state after annealing at 950 °C. The smallest quantum mechanical corrected equivalent oxide thickness measured was ∼1.37 nm. A large reduction of the leakage current density to 1.8 × 10^− 8 A/cm² at an electric field of 2 MV/cm was achieved by the annealing process.     

Preparation and characterization of indium zinc oxide thin films by electron beam evaporation technique

In this work, the preparation of In₂O₃-ZnO thin films by electron beam evaporation technique on glass substrates is reported. Optical and electrical properties of these films were investigated. The effect of dopant amount and annealing temperature on the optical and electrical properties of In₂O₃-ZnO thin films was also studied. Different amount of ZnO was used as dopant and the films were annealed at different temperature. The results showed that the most crystalline, transparent and uniform films with lowest resistivity were obtained using 25 wt% of ZnO annealed at 500 °C.     

Structural and electrical characteristics of chemical solution derived (Bi3.2La0.4Nd0.4)Ti3O12 thin films

(Bi_3.2La_0.4Nd_0.4)Ti₃O₁₂ (BLNT) thin films were prepared on Pt/Ti/SiO₂/Si substrates by using chemical solution deposition technique, and the effects of annealing temperatures in the range of 550-750 °C on structure and electrical properties of the thin films were investigated. X-ray diffraction analysis shows that the thin films have a bismuth-layered perovskite structure with preferred (117) orientation. The surface morphology observation by field-emission scanning electron microscopy confirms that films are dense and smooth with uniformly distributed grains. The grain size of the thin films increases with increasing annealing temperature; meanwhile, the structural distortion of the thin films also increases. It was demonstrated that the thin films show good electrical properties. The dielectric constant and dielectric loss are 191 and 0.028, respectively, at 10 kHz for the thin film annealed at 600 °C, and the 2Pr value of the thin film annealed at 700 °C is 20.5 μC/cm² at an electric field of 500 kV/cm.     

The effect of annealing on Al-doped ZnO films deposited by RF magnetron sputtering method for transparent electrodes

In this study, transparent conducting Al-doped zinc oxide (AZO) films with a thickness of 150 nm were prepared on Corning glass substrates by the RF magnetron sputtering with using a ZnO:Al (Al₂O₃: 2 wt.%) target at room temperature. This study investigated the effects of the post-annealing temperature and the annealing ambient on the structural, electrical and optical properties of the AZO films. The films were annealed at temperatures ranging from 300 to 500 °C in steps of 100 °C by using rapid thermal annealing equipment in oxygen. The thicknesses of the films were observed by field emission scanning electron microscopy (FE-SEM); their grain size was calculated from the X-ray diffraction (XRD) spectra using the Scherrer equation. XRD measurements showed the AZO films to be crystallized with strong (002) orientation as substrate temperature increases over 300 °C. Their electrical properties were investigated by using the Hall measurement and their transmittance was measured by UV-vis spectrometry. The AZO film annealed at the 500 °C in oxygen showed an electrical resistivity of 2.24 × 10^− 3 Ω cm and a very high transmittance of 93.5% which were decreased about one order and increased about 9.4%, respectively, compared with as-deposited AZO film.     

Preparation of aluminum doped zinc oxide films and the study of their microstructure, electrical and optical properties

Aluminum doped zinc oxide (AZO) polycrystalline thin films were prepared by sol-gel dip-coating process on optical glass substrates. Zinc acetate solutions of 0.5 M in isopropanol stabilized by diethanolamine and doped with a concentrated solution of aluminum nitrate in ethanol were used. The content of aluminum in the sol was varied from 1 to 3 at.%. Crystalline ZnO thin films were obtained following an annealing process at temperatures between 300 °C and 500 °C for 1 h. The coatings have been characterized by X-ray diffraction, UV-Visible spectrophotometry, scanning electron microscopy, and electrical resistance measurement. The ZnO:Al thin films are transparent (∼ 90%) in near ultraviolet and visible regions. With the annealing temperature increasing from 300 °C to 500 °C, the film was oriented more preferentially along the (0 0 2) direction, the grain size of the film increased, the transmittance also became higher and the electrical resistivity decreased. The X-ray diffraction analysis revealed single-phase ZnO hexagonal wurtzite structure. The best conductors were obtained for the AZO films containing 1 at.% of Al, annealed at 500 °C, 780 nm film thickness.     

Properties of Nb-doped ZnO transparent conductive thin films deposited by rf magnetron sputtering using a high quality ceramic target

Nb-doped ZnO films with (002) orientation have been grown on glass substrates by rf magnetron sputtering followed by vacuum annealing at 400°C for 3 h. The microstructures and surface figures of the Nbdoped ZnO films were investigated with X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. And its optical and electrical properties were measured at room temperature using a four-point probe technique and 756-type spectrophotometer, respectively. X-ray diffraction (XRD) revealed that the films are highly textured along the c axis and perpendicular to the surface of the substrate. After annealing at 400°C for 180 min under vacuum, transmittance of about 90% in visible region for Nb doped ZnO films was confirmed by the optical transmission spectra, and the low resistivity of 5·47 × 10⁻³ Ω·cm was obtained.     

Effect of annealing temperature on electrical and nano-structural properties of sol–gel derived ZnO thin films

Zinc oxide (ZnO) thin films have been prepared on silicon substrates by sol–gel spin coating technique with spinning speed of 3,000 rpm. The films were annealed at different temperatures from 200 to 500 °C and found that ZnO films exhibit different nanostructures at different annealing temperatures. The X-ray diffraction (XRD) results showed that the ZnO films convert from amorphous to polycrystalline phase after annealing at 400 °C. The metal oxide semiconductor (MOS) capacitors were fabricated using ZnO films deposited on pre-cleaned silicon (100) substrates and electrical properties such as current versus voltage (I–V) and capacitance versus voltage (C–V) characteristics were studied. The electrical resistivity decreased with increasing annealing temperature. The oxide capacitance was measured at different annealing temperatures and different signal frequencies. The dielectric constant and the loss factor (tanδ) were increased with increase of annealing temperature.     

Rapid thermal annealed Al-doped ZnO film for a UV detector

A low-resistive Al-doped ZnO (AZO) film was achieved by rapid thermal annealing. A co-sputtering method was used in the initial growth of AZO films and a rapid annealing process was performed on the as-deposited AZO film under N₂ atmosphere for 3 min. An as-deposited AZO film had an optical transmittance of 84.78% at 550 nm and a resistivity of 7.8 × 10^− 3 Ω cm. A rapid annealing process significantly improved the optical transmittance and electrical resistivity of the AZO film to 99.67% and 1 × 10^− 3 Ω cm, respectively. The structural changes of the AZO films were investigated by X-ray diffraction and transmission electron microscopy. The high quality AZO film was used to fabricate a metal-semiconductor-metal (MSM) structure for a UV detector. The MSM device provided a stable current of 25 μA at a bias of 2 V in a dark condition. Under UV illumination, the MSM device was highly responsive to UV light uniformly and repeatedly, and it enhanced the current by 80% at 45 μA. This rapid thermal annealing process may provide a useful method to fabricate quality AZO films for photoelectric applications with a low thermal budget.     

Growth and characterisation of electrodeposited ZnO thin films

The electrochemical method has been used to deposit zinc oxide (ZnO) thin films from aqueous zinc nitrate solution at 80 °C onto fluorine doped tin oxide (FTO) coated glass substrates. ZnO thin films were grown between − 0.900 and − 1.025 V vs Ag/AgCl as established by voltammogram. Characterisation of ZnO films was carried out for both as-deposited and annealed films in order to study the effect of annealing. Structural analysis of the ZnO films was performed using X-ray diffraction, which showed polycrystalline films of hexagonal phase with (002) preferential orientation. Atomic force microscopy was used to study the surface morphology. Optical studies identified the bandgap to be ∼ 3.20 eV and refractive index to 2.35. The photoelectrochemical cell signal indicated that the films had n-type electrical conductivity and current-voltage measurements showed the glass/FTO/ZnO/Au devices exhibit rectifying properties. The thickness of the ZnO films was found to be 0.40 μm as measured using the Talysurf instrument, after deposition for 3 min. Environmental scanning electron microscopy was used to view the cross-section of glass/FTO/ZnO layers.     

Effect of annealing on the structural,electrical and magnetic properties of Gd-implanted ZnO thin films

We report the results from structural, electrical and magnetic measurements on Gd-implanted ion beam deposited zinc oxide (ZnO) films. 40 keV Gd ions were implanted into 150 nm thick ZnO films with fluence 2.8 × 10¹⁵ cm⁻². RBS spectra reveal the implanted atoms are located in the near-surface region in as-implanted and up to 923 K annealed films, diffusing deeper into the films after 1073 K annealing. SEM images show that the average grain size increases from 10 to 30 nm upon annealing. High-resolution and energy-filtered transmission electron microscopy of a ZnO:Gd sample annealed at 923 K reveal the presence of Gd-rich regions in the film, but no evidence of pure Gd precipitates. Annealing increases the resistivity, and the carrier concentration decreases by as much as six orders of magnitude after annealing at up to 1073 K. All annealed films display a mix of paramagnetic, superparamagnetic and ferromagnetic behaviour extending to temperatures above 300 K that we attribute to the spatially inhomogeneous Gd distribution. The paramagnetic behaviour can be attributed to isolated Gd moments, while the ordered magnetic phases appear to arise from Gd-rich regions within the ZnO. X-ray absorption near edge spectroscopy provides evidence that there exist oxygen vacancies.     

Structural and electrical properties of sputtered indium-zinc oxide thin films

In this study, indium-zinc oxide (IZO) thin films have been prepared at a room temperature, 200 and 300 °C by radio frequency magnetron sputtering from a In₂O₃-12 wt.% ZnO sintered ceramic target, and their dependence of electrical and structural properties on the oxygen content in sputter gas, the substrate temperature and the post-heat treatment was investigated. X-ray diffraction measurements showed that amorphous IZO films were formed at room temperature (RT) regardless of oxygen content in sputter gas, and micro-crystalline and In₂O₃-oriented crystalline films were obtained at 200 and 300 °C, respectively. From the analysis on the electrical and the structural properties of annealed IZO films under Ar atmosphere at 200, 300, 400 and 500 °C, it was shown that oxygen content in sputter gas is a critical parameter that determines the local structure of amorphous IZO film, stability of amorphous phase as well as its eventual crystalline structure, which again decide the electrical properties of the IZO films. As-prepared amorphous IZO film deposited at RT gave specific resistivity as low as 4.48 × 10^− 4 Ω cm, and the highest mobility value amounting to 47 cm²/V s was obtained from amorphous IZO film which was deposited in 0.5% oxygen content in sputter gas and subsequently annealed at 400 °C in Ar atmosphere.     

Effect of rapid thermal annealing on Zn/ZnO layers

Zn/ZnO layers were deposited on SiO₂/Si substrate by magnetron sputtering at room temperature, and then these layers were annealed at various temperatures from 200 to 400 °C in nitrogen atmosphere for 1 min. The structural and electrical properties of the Zn/ZnO layers before and after annealing are systematically investigated by X-ray diffraction, scanning electron microscopy, current–voltage measurement system, and Auger electron spectroscopy. Current–voltage measurements show that the Zn/ZnO layers exhibit an Ohmic contact behavior. It is shown that, initially, the specific contact resistivity decreases with the increase of the annealing temperature and reaches a minimum value of 9.76 × 10^?5 Ω cm² at an annealing temperature of 300 °C. However, with a further increase of the annealing temperature, the Ohmic contact behavior degrades. This phenomenon can be explained by considering the diffusion of zinc interstitials and oxygen vacancies. It is also shown that Zn-rich ZnO thin films can be obtained by annealing Zn on the surface of ZnO film and that good Ohmic contact between Zn and ZnO layers can be observed when the annealing temperature was 300 °C.