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.     

Effect of dopants on the structural,optical and electrical properties of sol–gel derived ZnO semiconductor thin films

Undoped, Ga-, In-, Zr-, and Sn-doped ZnO transparent semiconductor thin films were deposited on alkali-free glasses by sol–gel method. 2-methoxyethanol (2-ME) and diethanolamine (DEA) were chosen as a solvent and a stabilizer, respectively. The doping concentration was maintained at 2 at.% in the impurity doping precursor solutions. The effects of different dopants on the structural, optical, and electrical properties of ZnO thin films were investigated. XRD results show that all annealed ZnO-based thin films had a hexagonal (wurtzite) structure. ZnO thin films doped with impurity elements obviously improved the surface flatness and enhanced the optical transmittance. All impurity doped ZnO thin films showed high transparency in the visible range (>91%). The Ga- and In- doped ZnO thin films exhibited higher Hall mobility and lower resistivity than did the undoped ZnO thin film.     

Influence of Ag doping on structural and optical properties of ZnO thin films synthesized by the sol–gel technique

Thin films of Ag–ZnO samples deposited on glass substrates with a different percentage of Ag content (1, 2, and 3 at%) were synthesized, at room temperature, by a dip-coating sol-gel method. The obtained samples are hexagonal wurtzite structure. The average grain size of deposits is about 5 nm. Up to 3 at%, c-axis lattice parameter shifts toward a higher value, which indicates that silver atoms replace Zn atoms in the crystal lattice. As shown by the DRX spectra, growth rate in the (101) direction is favored by the presence of silver ions in the ZnO. The layers present a homogeneous crystallites distribution, as we can remark it on SEM micrographs and exhibit a very low roughness according to AFM images. The entire samples exhibit a transmission value greater than 80 %, in the visible region, while the maximum is obtained for those doped at 2 at%. Energy band varies between 3.15 eV and 3.25 eV. The wider gap obtained is that of the ZnO layer doped with 2 at%. It is worth noting a strong UV emission observed on PL spectrum, performed at very low temperature (liquid nitrogen temperature), for silver doped ZnO compared to that of pure ZnO.     

Influence of post-deposition annealing on the structural and optical properties of ZnO thin films prepared by sol–gel and spin-coating method

Thin films of zinc oxide have been deposited onto (0001) sapphire substrate by sol–gel and spin-coating methods. The XRD pattern showed that the crystallinity of the annealed ZnO films had improved in comparison with that of the as-grown films. Photoluminescence spectra revealed a two-line structure, which is identified in terms of UV emission and defect-related emission. The emission intensity was found to be greatly dependent on heat treatment. Host phonons of ZnO and a shift of the _E2$E_2$ (high) peak from its position have been observed from Raman spectra. The surface morphologies of the film had been improved after annealing was observed from AFM images.     

Influence of drying conditions on the optical and structural properties of sol–gel-derived ZnO nanocrystalline films

Zinc oxide nanothin films were prepared on glass substrate by sol–gel dip-coating method using zinc acetate dihydrate, methanol, and monoethanolamine as precursor, solvent, and stabilizer, respectively. The relationship between drying conditions and the characteristics of ZnO nanocrystalline films (c-axis orientation, grain size, roughness and optical properties) was studied. The films were dried in an oven at different temperatures and by IR radiation. Then, the films were annealed at 500°C in a furnace. The chemical composition, transmission spectra, structure, and morphology of the samples were studied using infrared (IR) and UV–visible spectroscopy, X-ray diffraction (XRD), and atomic force microscopy (AFM), respectively. The XRD results show that the drying conditions affect the orientation of crystallization along the (0 0 2) plane. AFM images show that the thicknesses of the films decrease from 128 to 93 nm by changing the drying conditions. The photoluminescence (PL) of ZnO nanothin films shows the UV emission at near band edge and broad green radiation at about 465 nm wavelength.     

Influence of Mn doping on structural and optical properties of ZnO nano thin films synthesized by sol–gel technique

Undoped and Mn-doped ZnO samples with different percentages of Mn content (1, 5 and 10?at%) were synthesized by a dip-coating sol?Cgel method. We have studied the structural, chemical and optical properties of the samples by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV-visible spectroscopy. The XRD spectra show that all the samples are hexagonal wurtzite structures. We note that doping favors c-axis orientation along (002) planes. Up to 5?at% of Mn doping level, the c-axis lattice parameter shifts towards higher values with the increase of manganese content in the films. The expansion of the lattice constant of ZnO?CMn indicates that Mn is really doped into the ZnO. The SEM investigations of all samples revealed that the crystallites are of nanometer size. The surface quality of the ZnO?CMn film increases with Mn doping but no significant change of the grain size is observed from SEM images. The transmittance spectra show that the transparency of all the samples is greater than 85?%. We note, also, that a small doping (1?%) lowered the refractive index while the thickness of the layers and the gap increase. However, on raising the proportion of Mn beyond 5?%, practically the same values of index and gap as pure ZnO are found.     

Electrical and optical properties of Sb-doped ZnO thin films synthesized by sol–gel method

Sb-doped ZnO thin films with different values of Sb content （from 0 to 1.1 at.%） are deposited by the sol-gel dip- coating method under different sol concentrations. The effects of Sb-doping content, sol concentration, and annealing ambient on the structural, optical, and electrical properties of ZnO films are investigated. The results of the X-ray diffraction and ultraviolet-visible spectroscopy （UV-VIS） spectrophotometer indicate that each of all the films retains the wurtzite ZnO structure and possesses a preferred orientation along the c axis, with high transmittance （〉 90%） in the visible range. The Hall effect measurements show that the vacuum annealed thin films synthesized in the sol concentration of 0.75 mol/L each have an adjustable n-type electrical conductivity by varying Sb-doping density, and the photoluminescence （PL） spectra revealed that the defect emission （around 450 nm） is predominant. However, the thin films prepared by the sol with a concentration of 0.25 mol/L, despite their poor conductivity, have priority in ultraviolet emission, and the PL peak position shows first a blue-shift and then a red-shift with the increase of the Sb doping content.     

Electrical and optical properties of a-SexTe100–x thin films

The dc electrical conductivity of as deposited thin films of a-Se_xTe_100?x (x=3, 6, 9 and 12) is measured as a function of temperature range from 298 to 383 K. It is observed that the dc conductivity increases exponentially with the increase in temperature in this glassy system. The value of activation energy calculated from the slope of ln σ_dc vs. 1000/T plot, is found to decrease on incorporation of dopant (Se) content in the Te system. On the basis of pre-exponetial factor (σ₀), it is suggested that the conduction is due to thermally assisted tunneling of the carriers in the localized states near the band edges. The optical absorption measurements show an indirect optical band gap in this system and it decreases on increasing Se concentration. The optical constants (extinction coefficient (k) and refractive index (n)) do change significantly with the photon energy and also with the dopant Se concentration. The decrease in optical band gap may be due to the decrease in activation energy in the present system. It is also found that the real and imaginary parts of dielectric constants show a significant change with the photon energy as well as with the dopant concentration. With large absorption coefficients and compositional dependence of optical band gap and optical constants (n and k), these materials may be suitable for optical disk applications.     

Rapid thermal annealing effects on the structural and optical properties of Na–N codoped ZnO films

Polycrystalline ZnO thin films codoped with Na and N were obtained by chemical bath deposition. The structural characteristic and the optical properties of the rapid thermal annealed ZnO:(Na,N) films were investigated by X-ray diffraction, scanning electron microscopy, energy dispersive spectrometer (EDS), Raman spectrum and room-temperature photoluminescence. After RTA treatment, the XRD spectra showed a continuous decrease of the full- width at half-maximum (FWHM) of the (0 0 2) diffraction peak of the ZnO:(Na,N) film. The Raman spectra revealed that the intensity of the mode around 582 cm⁻¹ increased with the increase of the RTA temperature. The PL spectra showed different trends in the UV luminescence of ZnO:(Na,N) films after RTA treatments.     

Structural,electrical and optical properties of sol–gel AZO thin films

Transparent conductive Al-doped zinc oxide (AZO) thin films were prepared by a sol–gel method and their structural, electrical and optical properties were systematically investigated. A minimum resistivity of 4.2 × 10⁻³ Ω cm was obtained for the 650 °C-annealed films doped with 1.0 at.% Al. All films had the preferential c-axis oriented texture according to the X-ray diffraction (XRD) results. Optical transmittance spectra of the films showed a high transmittance of over 85% in the visible region and the optical band gap of the AZO films broadened with increasing doping concentration.     

Temperature dependent structural and optical properties of nanocrystallineCdO thin films deposited by sol–gel process

Nanocrystallites of cadmium oxide (CdO) thin films were deposited by sol–gel dip coating technique on glass and Si substrates. XRD and TEM diffraction patterns confirmed the nanocrystalline cubic CdO phase formation. TEM micrograph of the film revealed the manifestation of nano CdO phase with average particle size lying in the range 1.6–9.3 nm. UV–Vis spectrophotometric measurement showed high transparency (nearly 75% in the wavelength range 500–800 nm) of the film with a direct allowed bandgap lying in the range 2.86–3.69 eV. Particle size has also been calculated from the shift of bandgap with that of bulk value for the films for which the particles sizes are comparable to Bohr exitonic radius. The particle size increases with the increase in annealing temperature and also the intensity of XRD peaks increases which implies that better crystallinity takes place at higher temperature.This revised version was published online in August 2005 with a corrected issue number.     

Investigation of the structural and electrical properties of air-annealed ruthenium thin films on 6H–SiC at different temperatures

Ruthenium (Ru) Schottky contacts and thin films on n-type 6H–SiC were fabricated and characterised by physical and electrical methods. The characterisation was done after annealing the samples in air at various temperatures. Rutherford backscattering spectroscopy (RBS) analysis of the thin films indicated the oxidation of Ru after annealing at a temperature of 400 °C, and interdiffusion of Ru and Si at the Ru–6H–SiC interface at 500 °C. XRD analysis of the thin films indicated the formation of RuO₂ and RuSi in Ru–6H–SiC after annealing at a temperature of 600 °C. The formation of the oxide was also corroborated by Raman spectroscopy. The ideality factor of the Schottky barrier diodes (SBD) was seen to generally decrease with annealing temperature. The series resistance increased astronomically after annealing at 700 °C, which was an indication that the SBD had broken down. The failure mechanism of the SBD is attributed to deep inter-diffusions of Ru and Si at the Ru–6H–SiC interface as evidenced by the RBS of the thin films.     

The optical properties of MgxZnl-xO thin films

Mg_xZn_1-xO thin films have been prepared on silicon substrates by radio frequency magnetron sputtering at 60℃. The thin films have hexagonal wurtzite single-phase structure and a preferred orientation with the c-axis perpendicular to the substrates. The refractive indices of Mg_xZn_1-xO films are studied at room temperature by spectroscopic ellipsometry over the wavelength range of 400--760\,nm at the incident angle of 70℃. Both absorption coefficients and optical band gaps of Mg_xZn_1-xO films are determined by the transmittance spectra. While Mg content is increasing, the absorption edges of Mg_xZn_1-xO films shift to higher energies and band gaps linearly increase from 3.24.eV at x=0 to 3.90\,eV at x=0.30. These results provide important information for the design and modelling of ZnO/ Mg_xZn_1-xO heterostructure optoelectronic devices.     

Some optical properties of Ge–S amorphous thin films

Amorphous Ge_xS_1−x films (x=0.27, 0.32, 0.36 and 0.4) were prepared by thermal evaporation. The values of the refractive index, the optical gap and the parameters of the Wemple–DiDomenico single oscillator model were determined. Using Miller's generalized rule the values of the third-order non-linear susceptibility were also estimated. Thermally induced bleaching was observed for films studied. Photobleaching was observed for sulfur rich and nearly stoichiometric films (x=0.27, 0.32) while for a germanium rich film (x=0.4) no response to the illumination was observed. The differences in photobleaching are attributed to the role of p-lone pair states and to an overall network rigidity of the films.     

Annealing induced transformations in structural and optical properties of Ge30Se70−xBix thin films

ABSTRACT

Thin films of Ge₃₀Se_70?xBi_x (x?=?5, 15, 20) were prepared by thermal evaporation method on glass substrates with thickness 800?nm. The films were annealed at 250°C and 320°C for 2?h to study the annealing-induced structural and optical change. The X-ray diffraction characterization revealed the amorphous to crystalline phase transformation with annealing. The indirect optical band gap decreased with annealing which is explained on the basis of phase transformation and density of localized states. The formation of surface dangling bonds around the crystallites during crystallization process reduced the band gap. The Tauc parameter and Urbach energy change show the degree of chemical disorderness in the films. The transmitivity decreased while the absorption coefficient increased with the annealing process. The microstructural study done by Field emission scanning electron microscopy shows the formation of crystallites upon annealing. Atomic force microscopy investigation on these films shows the influence of annealing on surface topography.     

Effect of sputtering pressure on structural and optical properties of silver oxide thin films; Kramers–Kronig method

Silver oxide nano layers were prepared by RF magnetron sputtering on amorphous SiO₂ substrates. O₂ pressure in chamber was varied from 1 to 4 and 7 mTorr during growth process. The effects of different O₂ pressure on structural, morphological and optical properties of the films were investigated by means of X-ray diffraction, scanning electron microscopy, atomic force microscopy and UV–Vis spectroscopy analyses. Optical reflectance measured in the wavelength of 350–950 nm by spectroscopy. Other optical properties and optical band gaps were calculated using Kramers–Kronig relations. The X-ray diffraction measurements showed change in crystalline structure with increasing O₂ pressure. Preferred orientation has been changed to another growth orientation at 4 mTorr O₂ pressure. The Atomic force microscope images showed increasing in roughness consistently by increasing oxygen pressure. The thickness of the thin films decreases (from 217 to 180 nm) with increasing O₂ pressure. Optical results revealed that the highest optical band gap of 3.1 eV and the highest transmittance of?~?80% were achieved at lower O₂ pressure (1 mTorr).