Optical Properties Of Zinc Oxide Films Research Articles

Structural and optical properties of copper doped ZnO films derived by sol–gel

Undoped and copper doped ZnO (ZnO:Cu) films were prepared by sol–gel spin coating technique. The effect of Cu incorporation on the structural, morphological and optical properties of the Zinc oxide (ZnO) film was investigated. The chemical composition of the Cu doped ZnO films was confirmed by XPS and XRD measurements. The structural disorder was observed in XRD spectra depending on the Cu incorporation and these results were confirmed by the increasing Urbach energy values. The refractive index dispersion was analyzed by single oscillator model developed by Wemple and DiDomenico. The oscillator energy and dispersion energy values for the films were determined. The oscillator energy value Eo for the ZnO film decreases with Cu incorporation due to increase in the probability of electronic transitions between electronic bands. It is evaluated that the structural and optical properties of ZnO films can be controlled with Cu doping.

Epitaxial growth of ZnO films at extremely low temperature by atomic layer deposition with interrupted flow

Thin crystalline films of zinc oxide (ZnO) of high quality have been grown epitaxially on a (0 0 0 1) c-plane of a sapphire substrate with atomic layer deposition (ALD) at extra-low temperature. With diethylzinc (DEZn) and deionized water as precursors in combination with interrupted flow, we obtained ZnO thin films with an optimal growth window in a range 25–160 °C, so effectively lowering the growth temperature by about 120 °C relative to the conventional method involving a continuous-flow. We characterized the microstructure of these films with X-ray reflectivity and high-resolution X-ray diffraction (XRD) measurements. The XRD results indicate that the stock time might extend the reaction of DEZn and water through an increased duration. This low temperature for growth results in increased crystalline quality and reduced the non-radiative recombination process to enhance the optical properties of ZnO films.

Optical Properties of Zinc-oxide Films Determined UsingSpectroscopic Ellipsometry with Various Dispersion Models

Optical Properties of Zinc-oxide Films Determined UsingSpectroscopic Ellipsometry with Various Dispersion Models

Enhanced redshift of the optical band gap in Sn-doped ZnO free standing films using the sol–gel method

The optical band gap in free standing transparent zinc oxide (ZnO) films using the sol–gel method was studied. The effect of Sn doping on grain size, vibrational structure and on the optical properties of ZnO films was investigated. Contrary to the common observation, the optical band gap of Sn-doped ZnO is red-shifted from 3.38 to 3.18 eV as the doping weight percentage is increased to 3%. The redshift of the optical band gap is due to the deep states in the band gap, and a change of ∼0.2 eV can only be observed when a substrate is not used. This study illustrates that removal of interaction between film boundaries and substrate is essential for developing effective band gap-tunable ZnO thin films.

Nanocrystalline ZnO thin film growth by ultrasonic spray from a non-aqueous solution

In the present work, zinc oxide (ZnO) thin films are deposited by the ultrasonic spray method. In order to study the influence of the nature of the precursor solution, zinc acetate and zinc nitrate salts dissolved in methanol are used respectively to prepare two non-aqueous starting solutions. The influence of substrate temperature on the structural growth kinetics and optical properties of ZnO films is also investigated. For this purpose, the substrate temperature is varied in the range of 250—400°C. X-ray diffraction (XRD) analysis reveals that at low temperature the films that are grown contain nanocrystallites with a privileged orientation depending on the nature of the starting precursor; these privileged orientations correspond to the plane (100) for the films deposited with zinc acetate and (002) for films prepared with zinc nitrate precursor. However, with increasing deposition temperature, the privileged orientation disappears. The growth kinetics is closely related to the substrate temperature and to the nature of the starting solution. The scanning electron microscopy (SEM) observations suggest that the liquid droplets react once they reach the substrate surface when zinc acetate precursor is used. However, in the case of zinc nitrate solution, the droplets spread first on the substrate surface followed by the subsequent surface reaction. This difference is explained in terms of the dissociation enthalpy of both solutions.

Effect of oxygen pressure on the optical properties of ZnO/Si(100) thin films deposited by femtosecond pulse laser

Zinc oxide （ZnO） thin films have been grown on n type Si （100） substrate using femtosecond pulsed laser deposition （PLD）. The effect of change in parameters, including substrate temperature, laser energy and oxygen pressure, on the structure and optical properties of ZnO films is discussed. The Xray diffraction results show that the ZnO films are highly caxis oriented when deposited at substrate temperature of 80?℃ with laser energy of 1\^5?mJ under oxygen pressure of 10 mPa. The field emission scanning electron microscopy indicates that the mean grain size increases with the increase of temperature, but decreases with the increase of laser energy. The ultravioletvisible transmissivity shows that the annealed films have a transmittance of 90% in visible rang. The photoluminescence spectra of ZnO films are discussed. In comparison, the structure and photoluminesceme properties of ZnO films produced by using nanosecond PLD are also studied.

Electrical and optical properties of ZnO films grown by molecular beam epitaxy

Zinc oxide (ZnO) films have been grown on sapphire by molecular beam epitaxy (MBE), and it is found that the grain size of the ZnO films increased with increasing the growth temperature. Photoluminescence (PL) study shows that the intensity ratio of near-band-edge emission to deep-level-related emission (NBE/DL) of the ZnO is significantly enhanced with increasing the growth temperature, and the dependence of the carrier mobility on the growth temperature shows very similar trend, which implies that there is a community factor that determines the optical and electrical properties of ZnO, and this factor is suggested to be the grain boundary. The results obtained in this paper reveal that by reducing the grain boundaries, ZnO films with high optical and electrical properties may be acquired.

Effect of thermal annealing on the structural and optical properties of nanostructured zinc oxide thin films prepared by pulsed laser ablation

Zinc oxide (ZnO) films are prepared by pulsed laser ablation, on an optically flat quartz substrate for different deposition time. The influence of annealing temperature, on the structural and optical properties of ZnO films is investigated systematically using X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX), scanning electron microscopy (SEM), atomic force microscopy (AFM), Raman spectra, UV–vis spectroscopy and photoluminescence spectroscopy (PL). The XRD pattern shows that the as-deposited films are amorphous and the annealed films are polycrystalline. The average size of the crystalline grains varies from 9 to 26 nm in the films. The SEM and AFM images reveal uniform distribution of grains in the films and the grains are in the nanoscale dimension. Raman spectra suggest the hexagonal wurtzite phase for the ZnO films. The UV–visible spectra show an increase in transmittance with annealing temperature. The observation of very intense PL emission from the films annealed at 773 K, suggest the suitability of these films for applications as light emitters in the visible region. The ability to produce the stochiometric ZnO thin films with reproducible structural, morphological and optical characteristics should be useful as a suitable window material for practical industrial solar cell and display devices.

Optical properties of ZnO films grown by atmospheric-pressure chemical vapor deposition using Zn and H 2O as source materials

Zinc oxide (ZnO) films grown by atmospheric-pressure chemical vapor deposition using Zn powder and water (H 2O) as source materials were investigated by photoluminescence (PL), photoacoustic (PA), Raman scattering, infrared (IR) absorption and attenuated total reflection (ATR) measurements. PL results suggested that the concentration of oxygen vacancy ( V O) can be controlled by adjusting the source feed ratio of H 2O to Zn (VI/II). PA measurements revealed that an absorption edge shifted to lower energies with increasing VI/II. It was also found that the increase in VI/II contributed to the decrease in resistivity. Raman, IR absorption and ATR spectra showed that the films contained high concentrations of hydrogen atoms. There is a possibility that the increase in concentration of hydrogen related donors contributes to both the VI/II dependence of PA spectrum and that of resistivity.

Comprehensive study of ZnO films prepared by filtered cathodic vacuum arc at room temperature

Room temperature deposition of high crystal quality zinc oxide (ZnO) films was realized by the filtered cathodic vacuum arc (FCVA) technique. Detrimental macroparticles in the plasma as byproducts of arcing process are removed with an off-plane double bend magnetic filter. The influence of oxygen pressure on the structural, electrical and optical properties of ZnO films were investigated in detail. The crystal structure of ZnO is hexagonal with highly c-axis orientation. Intrinsic stress decreases with an increase of chamber pressure, and near stress-free film was obtained at 1×10−3 Torr. Films with optical transmittance above 90% in the visible range and resistivity as low as 4.1×10−3 Ω cm were prepared at pressure of 5×10−4 Torr. Energetic zinc particles in the cathodic plasma and low substrate temperature enhance the probability of formation of zinc interstitials in the ZnO films. The observation of strong ultraviolet photoluminescence and weak deep level emission at room temperature manifest the high crystal quality of the ZnO films prepared by FCVA. Enlargement of the band gap is observed in the absorption and photoluminescence spectra, the band gap shifts towards lower energy with an increase of oxygen pressure. This phenomenon is attributed to the Burstein–Moss effect.

Photoluminescence study of ZnO films prepared by thermal oxidation of Zn metallic films in air

Zinc oxide (ZnO) films were synthesized by thermal oxidation of metallic zinc films in air. The influence of annealing temperatures ranging from 320 to 1000 °C on the structural and optical properties of ZnO films is investigated systematically using x-ray diffraction and room temperature photoluminescence (PL). The films show a polycrystalline hexagonal wurtzite structure without preferred orientation. Room temperature PL spectra of the ZnO films display two emission bands, predominant excitonic ultraviolet (UV) emission and weak deep level visible emission. It is observed that the ZnO film annealed at 410 °C exhibits the strongest UV emission intensity and narrowest full width at half maximum (81 meV) among the temperature ranges studied. The excellent UV emission from the film annealed at 410 °C is attributed to the good crystalline quality of the ZnO film and the low rate of formation of intrinsic defects at such low temperature. The visible emission consists of two components in the green and yellow range, and they show different temperature dependent behavior from UV emission. Their possible origins are discussed.

Effects of the position substrate upon the structural behaviour, electrical and optical properties of zinc-oxide films used in solar cells

The preparation by the rf sputtering technique and characterisation of ZnO thin films used as windows in solar cells are described. The electrical behaviour and structural spectra clearly show an important effect of the substrate position with respect to the target. In fact, among all the studied substrate positions, only the samples facing the target are randomly oriented having the mixed orientation (100), (002) and (101). All the others have the c(002)-axis orientation. The scanning electron-microscope observations confirm the X-ray analysis results. The last samples have a resistivity as low as 10−3Ωcm while the randomly-oriented, ones have a large resisivity of about 102−103Ωcm These latter show, in their transmittance characteristics, a slight shift towards higher wavelengths. However, no effect is noticed when the other samples are optically assessed. Consequently, the optical gap is found to be about 3.38 eV for the conducting films and 3.3 eV for the ones having a higher resistivity. The average transmittance in the visible range is around 85–90% for all the samples