Electrical and structural properties of In-doped ZnO films deposited by RF superimposed DC magnetron sputtering system

Zinc-indium-oxide (ZIO) films were deposited on non-alkali glass substrates by RF superimposed DC magnetron sputtering with a ZIO (9.54 wt% In₂O₃ content) high-density, sintered target at room temperature. The electrical, structural and optical properties of the ZIO films deposited with different sputtering parameters were examined. The total power for RF superimposed DC magnetron sputtering was 80 W. The RF power ratio in the total sputtering power was changed from 0 to 100% in steps of 25%. The ZIO films deposited with a 100% RF discharge showed the lowest resistivity, 1.28×10⁻³ Ω cm, due to the higher carrier concentration. The ZIO film deposited at 50% RF power showed a relatively larger grain size and smaller FWHM. XPS suggested an increase in the level of In³⁺ substitution for Zn²⁺ in the ZnO lattice with increasing RF/(DC+RF) due to the low damage process. The average transmittance of all ZIO films in the visible light region was >80%. The increasing RF power portion of the total sputtering power led to a broadening of the optical band gap, which was attributed to the increase in carrier density according to Burstein-Moss shift theory.     

Optical properties of p-type CuAlO2 thin film grown by rf magnetron sputtering

We report the structural and optical properties of copper aluminium oxide (CuAlO₂) thin films, which were prepared on c-plane sapphire substrates by the radio frequency magnetron sputtering method. X-ray photoelectron spectroscopy (XPS) along with X-ray diffraction (XRD) analysis confirms that the films consist of delafossite CuAlO₂ phase only. The optical absorption studies show the indirect and direct bandgap is 1.8 eV and 3.45 eV, respectively. Room temperature photoluminescence (PL) measurements show three emission peaks at 360 nm (3.45 eV), 470 nm (2.63 eV) and 590 nm (2.1 eV). The first one is near band edge emission while the other two are originated from defects.     

Structural and optical properties of zinc nitride films prepared by rf magnetron sputtering

Zinc nitride films were prepared on quartz substrates by rf magnetron sputtering using pure zinc target in N₂-Ar plasma. X-ray diffraction (XRD) analysis indicates that the films just after deposition are polycrystalline with a cubic structure and a preferred orientation of (4 0 0). X-ray photoelectron spectroscopy (XPS) analysis also confirms the formation of N-Zn bonds and the substitution incorporation of oxygen for nitrogen on the surface of the films. The optical band gap is calculated from the transmittance spectra of films just after deposition, and a direct band gap of 1.01 ± 0.02 eV is obtained. Room temperature PL measurement is also performed to investigate the effect of defect on the band gap and quality of the zinc nitride films.     

Structural, electrical and optical properties of Gd doped and undoped ZnO:Al (ZAO) thin films prepared by RF magnetron sputtering

The influence of the gadolinium doping on the structural features and opto-electrical properties of ZnO:Al (ZAO) films deposited by radio frequency (RF) magnetron sputtering method onto glass substrates was investigated. X-ray analysis showed that the films were polycrystalline fitting well with a hexagonal wurtzite structure and have preferred orientation in [0 0 2] direction. The Gd doped ZAO film with a thickness of 140 nm showed a high visible region transmittance of 90%. The optical band gap was found to be 3.38 eV for pure ZnO film and 3.58 eV for ZAO films while a drop in optical band gap of ZAO film was observed by Gd doping. The lowest resistivities of 8.4 × 10⁻³ and 10.6 × 10⁻³ Ω cm were observed for Gd doped and undoped ZAO films, respectively, which were deposited at room temperature and annealed at 150 °C.     

Room-temperature deposition of transparent conducting Al-doped ZnO films by RF magnetron sputtering method

Transparent conductive Al-doped zinc oxide (AZO) films with highly (0 0 2)-preferred orientation were deposited on quartz substrates at room temperature by RF magnetron sputtering. Optimization of deposition parameters was based on RF power, Ar pressure in the vacuum chamber, and distance between the target and substrate. The structural, electrical, and optical properties of the AZO thin films were investigated by X-ray diffraction, Hall measurement, and optical transmission spectroscopy. The 250 nm thickness AZO films with an electrical resistivity as low as 4.62 × 10⁻⁴ Ω cm and an average optical transmission of 93.7% in the visible range were obtained at RF power of 300 W, Ar flow rate of 30 sccm, and target distance of 7 cm. The optical bandgap depends on the deposition condition, and was in the range of 3.75-3.86 eV. These results make the possibility for light emitting diodes (LEDs) and solar cells with AZO films as transparent electrodes, especially using lift-off process to achieve the transparent electrode pattern transfer.     

Effects of electron irradiation on the properties of GZO films deposited with RF magnetron sputtering

Transparent conductive GZO films were deposited on polycarbonate substrates by electron beam assisted radio frequency (RF) magnetron sputtering and then the influence of electron irradiation on the structural, optical and electrical properties of GZO films was investigated by using X-ray diffractometry, UV-vis spectrophotometry, four point probes, atomic force microscopy and UV photoelectron spectroscopy. Sputtering power was kept constant at 3 W/cm² during deposition, while electron irradiation energy varied from 450 to 900 eV.Electron irradiated GZO films show larger grain sizes than those of films prepared without electron irradiation, and films irradiated at 900 eV show higher optical transmittance in the visible wavelength region and lower sheet resistance (120 Ω/□) than other films. The work-function is also increased with electron irradiation energy. The highest work-function of 4.4 eV was observed in films that were electron irradiated at 900 eV.     

Effects of annealing temperature and method on structural and optical properties of TiO2 films prepared by RF magnetron sputtering at room temperature

TiO₂ thin film was deposited on non-heated Si(1 0 0) substrate by RF magnetron sputtering. The as-deposited films were annealed by a conventional thermal annealing (CTA) and rapid thermal annealing (RTA) at 700 and 800 °C, and the effects of annealing temperature and method on optical properties of studied films were investigated by measuring the optical band gaps and FT-IR spectra. And we also compared the XRD patterns of the studied samples. The as-deposited film showed a mixed structure of anatase and brookite. Only rutile structures were found in samples annealed above 800 °C by CTA, while there are no special peaks except the weak brookite B(2 3 2) peak for the sample annealed at (or above) 800 °C by RTA. FT-IR spectra show the broad peaks due to Ti-O vibration mode in the range of 590-620 cm⁻¹ for the as-deposited film as well as samples annealed by both annealing methods at 700 °C. The studied samples all had the peaks from Si-O vibration mode, which seemed to be due to the reaction between TiO₂ and Si substrate, and the intensities of these peaks increased with increasing of annealing temperature. The optical band gap of the as-deposited film was 3.29 eV but it varied from 3.39 to 3.43 eV as the annealing temperature increased from 700 to 800 °C in the samples annealed by CTA. However, it varied from 3.38 to 3.32 eV as the annealing temperature increased from 700 to 800 °C by RTA.     

Effects of the sputtering time of ZnO buffer layer on the quality of GaN thin films

ZnO thin films with different thickness (the sputtering time of ZnO buffer layers was 10 min, 15 min, 20 min, and 25 min, respectively) were first prepared on Si substrates using radio frequency magnetron sputtering system and then the samples were annealed at 900 °C in oxygen ambient. Subsequently, a GaN epilayer about 500 nm thick was deposited on ZnO buffer layer. The GaN/ZnO films were annealed in NH₃ ambient at 950 °C. X-ray diffraction (XRD), atom force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) were used to analyze the structure, morphology, composition and optical properties of GaN films. The results show that their properties are investigated particularly as a function of the sputtering time of ZnO layers. For the better growth of GaN films, the optimal sputtering time is 15 min.     

A comparative study of the microstructures and optical properties of Cu- and Ag-doped ZnO thin films

Cu- and Ag-doped ZnO films were deposited by direct current co-reactive magnetron sputtering technique. The microstructure, the chemical states of the oxygen, zinc, copper and silver and the optical properties in doped ZnO films were investigated by X-ray diffraction spectroscopy (XRD), X-ray photoelectron spectroscopy (XPS) and UV-Visible spectroscopy. XRD analysis revealed that both of Cu- and Ag-doped ZnO films consist of single phase ZnO with zincite structure while the doping elements had an evident effect on the (0 0 2) preferential orientation. The XPS spectra showed that the chemical states of oxygen were different in Cu- and Ag-doped ZnO thin films, which may lead to the shift of the band gap as can be observed in the transmittance and absorption spectra. Meanwhile, the widths of band tails of ZnO films became larger after Cu and Ag doping.     

The characterization of fluorocarbon films on NiTi alloy by magnetron sputtering

Fluorocarbon films were deposited on nickel-titanium (NiTi) alloy substrate by radio-frequency (RF, 13.56 MHz) magnetron sputtering using a polytetrafluoroethylene (PTFE) target. The deposition parameters of fluorocarbon films including the RF power, the working gas pressure and Ar flow rate were systematically studied. The structure of the deposited films was studied by attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS). The surface morphology of the deposited films was measured by atomic force microscopy (AFM). The mechanical properties of the deposited films were characterized by a nanoindenter. C-Fx and C-C units were found in the deposited fluorocarbon films, which corresponded to the results of XPS. The surface roughness of the fluorocarbon film was 7.418 nm (Ra).     

Effect of annealing on the properties of N-doped ZnO films deposited by RF magnetron sputtering

N-doped ZnO films were deposited by RF magnetron sputtering in N₂/Ar gas mixture and were post-annealed at different temperatures (T_a) ranging from 400 to 800 °C in O₂ gas at atmospheric pressure. The as-deposited and post-annealed films were characterized by their structural (XRD), compositional (SIMS, XPS), optical (UV-vis-NIR spectrometry), electrical (Hall measurements), and optoelectronic properties (PL spectra). The XRD results authenticate the improvement of crystallinity following post-annealing. The weak intensity of the (0 0 2) reflection obtained for the as-deposited N-doped ZnO films was increased with the increasing T_a to become the preferred orientation at higher T_a (800 °C). The amount of N-concentration and the chemical states of N element in ZnO films were changed with the T_a, especially above 400 °C. The average visible transmittance (400-800 nm) of the as-deposited films (26%) was increased with the increasing T_a to reach a maximum of 75% at 600 °C but then decreased. In the PL spectra, A⁰X emission at 3.321 eV was observed for T_a = 400 °C besides the main D⁰X emission. The intensity of the A⁰X emission was decreased with the increasing T_a whereas D⁰X emission became sharper and more optical emission centers were observed when T_a is increased above 400 °C.     

化学水浴法和磁控溅射法制备硫化镉薄膜的性能研究

以氯化铵、氯化镉、氢氧化钾和硫脲为反应物采用化学水浴法制备了硫化镉薄膜,为了作对比研究,采用射频磁控溅射以硫化镉为靶材,氩气为溅射气体,制备了硫化镉薄膜。采用X射线衍射、扫描电子显微镜和紫外-可见光光谱仪分别表征了硫化镉薄膜的结构、形貌和光学吸收特性。结果表明,采用以上两种方法制备的硫化镉均具有(002)择优取向,溅射法制备的硫化镉薄膜较致密,薄膜表面较光滑,平均晶粒尺寸在20～30nm;水浴法制备的硫化镉薄膜颗粒尺寸较小,缺陷较多。除了在短波段溅射所得硫化镉薄膜的透过率略差于水浴法所得硫化镉薄膜之外,溅射法制备的硫化镉薄膜的性能整体上优于水浴法制备的薄膜。两种方法制备的硫化镉薄膜的能隙在2.3～2.5eV。     

Ti-incorporated ZnO films synthesized via magnetron sputtering and its optical properties

Undoped and Ti-doped ZnO films were deposited using radio frequency reactive magnetron sputtering at various sputtering powers. The crystal structures, surface morphology, chemical state and optical properties in Ti-doped ZnO films were systematically investigated via X-ray diffraction (XRD), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and ultraviolet visible (UV–Vis) spectrophotometer. Results indicated that titanium atoms may replace zinc atomic sites substitutionally or incorporate interstitially in the hexagonal lattices, and a moderate quantity of Ti atoms exist in the form of sharing the oxygen with Zn atoms and hence improve the (0 0 2) orientation. The photoluminescence (PL) spectra of the Ti-doped ZnO films contain one main blue peak, whose intensity increased with the increase of sputtering power. Our results indicated that a higher compressive stress in Ti-doped ZnO films results in a lower optical band gap and a lower transmittance, and various Ti impurities can affect the concentration of the interstitial Zn and O vacancies.     

Optical and electrical properties of nanocrystal zinc oxide films prepared by dc magnetron sputtering at different sputtering pressures

The nanocrystal thin films of zinc oxide doped by Al (ZnO:Al) were deposited by dc reactive magnetron sputtering on the glass substrates, in the pressure range of 33-51 Pa. From the X-ray diffraction patterns, the nanocrystalline structure of ZnO:Al films and the grain size were determined. The optical transmission spectra depend from the sputtering pressure, but their average value was 90% in the range from 33 Pa to 47 Pa. Also, the sputtering pressure changes the optical band gap of ZnO:Al films, which is highest for films deposited at 37 Pa, 40 Pa and 47 Pa. The obtained films at room temperature have a sheet resistance of 190 Ω/cm² which increases with time, but the films annealed at temperature of 400 °C have constant resistance. The surface morphology of the films was studied by Scanning electron microscopy. XPS spectra showed that the peak of O1s of the as-deposited films is smaller than the peak of the annealed ZnO:Al films.     

Structural and optical properties of amorphous hydrogenated silicon carbonitride films produced by PECVD

Amorphous hydrogenated silicon carbonitride thin films (a-Si:C:N:H), deposited by plasma enhanced chemical vapour deposition (PECVD) using hexamethyldisilazane (HMDSN) as monomer and Ar as feed gas, have been investigated for their structural and optical properties as a function of the deposition RF plasma power, in the range of 100-300 W. The films have been analysed by Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), UV-vis-NIR spectrophotometry and atomic force microscopy (AFM). From the analysis of the FT-IR spectra it results that the films become more amorphous and inorganic as RF plasma power increases. The incorporation of oxygen in the deposited layers, mainly due to the atmospheric attack, has been evaluated by XPS and FT-IR spectroscopy. Reflectance/transmittance spectra, acquired in the range of 200-2500 nm, allow to descrive the film absorption edge for interband transitions. A relationship between the optical energy band gap, deduced from the absorption coefficient curve, and the deposition RF plasma power has been investigated. The reduction of the optical energy gap from 3.85 to 3.69 eV and the broadening of the optical absorption tail with RF plasma power increasing from 100 to 300 W are ascribed to the growth of structural disorder, while the increase of the refractive index, evaluated at 630 nm, is attributed to a slight densification of the film. The AFM analysis confirms the amorphous character of the films and shows how the deposited layers become rougher when RF plasma power increases. The wettability of the film has been studied and related to the chemical composition and to the morphology of the deposited layers.     

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.     

Deposition of Ni, Ag, and Pt-based Al-doped ZnO double films for the transparent conductive electrodes by RF magnetron sputtering

Ni, Ag, and Pt-based Al-doped ZnO (AZO) films have been deposited as transparent conductivity layers on quartz by RF magnetron sputtering and characterized by X-ray diffraction, Hall measurement, optical transmission spectroscopy, scanning electron microscopy (SEM). The deposition of thicker metal layer in double layers resulted in lowering the effective electrical resistivity with a slight reduction of their optical transmittance. A film consisting of AZO (250 nm)/Ni (2 nm) double structure, exhibits a sheet resistance of 21.0 Ω/sq, a high transmittance of 76.5%, and characterize good adhesion to substrate. These results make the satisfactory for GaN-based light-emitting diodes (LEDs) and solar cells with metal-based AZO double films as current spread layers.     

Microstructures and optical properties of Cu-doped ZnO films prepared by radio frequency reactive magnetron sputtering

Pure and Cu-doped ZnO (ZnO:Cu) thin films were deposited on glass substrates using radio frequency (RF) reactive magnetron sputtering. The effect of substrate temperature on the crystallization behavior and optical properties of the ZnO:Cu films have been studied. The crystal structures, surface morphology and optical properties of the films were systematically investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and a fluorescence spectrophotometer, respectively. The results indicated that ZnO films showed a stronger preferred orientation toward the c-axis and a more uniform grain size after Cu-doping. As for ZnO:Cu films, the full width at half maxima (FWHM) of (0 0 2) diffraction peaks decreased first and then increased, reaching a minimum of about 0.42° at 350 °C and the compressive stress of ZnO:Cu decreased gradually with the increase of substrate temperature. The photoluminescence (PL) spectra measured at room temperature revealed two blue and two green emissions. Intense blue-green luminescence was obtained from the sample deposited at higher substrate temperature. Finally, we discussed the influence of annealing temperature on the structural and optical properties of ZnO:Cu films. The quality of ZnO:Cu film was markedly improved and the intensity of blue peak (∼485 nm) and green peak (∼527 nm) increased noticeably after annealing. The origin of these emissions was discussed.     

Unidirectional variation of lattice constants of Al-N-codoped ZnO films by RF magnetron sputtering

Al-N-codoped ZnO films were fabricated by RF magnetron sputtering in the ambient of N₂ and O₂ on silicon (1 0 0) and homo-buffer layer, subsequently, annealed in O₂ at low pressure. X-ray diffraction (XRD) spectra show that as-grown and 600 °C annealed films grown by codoping method are prolonged along crystal c-axis. However, they are not prolonged in (0 0 1) plane vertical to c-axis. The films annealed at 800 °C are not prolonged in any directions. Codoping makes ZnO films unidirectional variation. X-ray photoelectron spectroscopy (XPS) shows that Al content hardly varies and N escapes with increasing annealing temperature from 600 °C to 800 °C.     

An extreme change in structural and optical properties of indium oxynitride deposited by reactive gas-timing RF magnetron sputtering

The indium oxynitride (InON) films were achieved by reactive RF magnetron sputtering indium target which has the purity of 99.999% with a novel reactive gas-timing technique. The structural, optical and electrical properties in a series of polycrystalline InON films affected by gas-timing of reactive N₂ and O₂ gases introduced to the chamber were observed. The X-ray photoelectron spectroscopy revealed that the oxygen content in thin films that compounded to indium and nitrogen, which increased from 10% in indium nitride (InN) to 66% in indium oxide (In₂O₃) films. The X-ray diffraction peaks show that the phase of deposited films changes from InN to InON and to In₂O₃ with an increasing oxygen timing. The hexagonal structure of InN films with predominant (0 0 2) and (0 0 4) orientation was observed when pure nitrogen is only used as sputtering gas, while InON and In₂O₃ seem to demonstrate body-center cubic polycrystalline structures depending on gas-timing. The surface morphologies investigated from atomic force microscope of deposited films with varying gas-timing of O₂:N₂ show indifferent. The numerical algorithm method was used to define the optical bandgap of films from transmittance results. The increasing oxygen gas-timing affects extremely to the change of crystallinity phase from InN to InON and to In₂O₃, the increase of optical bandgap from 1.4 to 3.4 eV and the rise of sheet resistance from 15 Ω/□ to insulator.