Thickness dependent properties of nickel oxide thin films deposited by dc reactive magnetron sputtering

Nickel oxide thin films of various thicknesses were grown on glass substrates by dc reactive magnetron sputtering technique in a pure oxygen atmosphere with sputtering power of 150 W and substrate temperature of 523 K. Crystalline properties of NiO films as a function of film thickness were investigated using X-ray diffraction. XRD analysis revealed that (200) is the preferred orientation and the orientation of the films changed from (200) to (220) at film thickness of 350 nm. The maximum optical transmittance of 60% and band gap of 3.82 eV was observed at the film thickness of 350 nm. The lowest electrical resistivity of 5.1 Ω cm was observed at a film thickness of 350 nm, thereafter resistivity increases with film thickness.     

Mn-doped ZnO transparent conducting films deposited by DC magnetron sputtering

Mn-doped zinc oxide (ZnO:Mn) thin films with low resistivity and relatively high transparency were firstly prepared on glass substrate by direct current (DC) magnetron sputtering at room temperature. Influence of film thickness on the properties of ZnO:Mn films was investigated. X-ray diffraction (XRD) and scanning electron microscopy (SEM) show that all the deposited films are polycrystalline with a hexagonal structure and have a preferred orientation along the c-axis perpendicular to the substrate. As the thickness increases from 144 to 479 nm, the crystallite size increases while the electrical resistivity decreases. However, as the thickness increases from 479 to 783 nm, the crystallite size decreases and the electrical resistivity increases. When film thickness is 479 nm, the deposited films have the lowest resistivity of 2.1 × 10^− 4 Ω cm and a relatively high transmittance of above 84% in the visible range.     

Substrate temperature dependent morphology and resistivity of pulsed laser deposited iridium oxide thin films

Iridium oxide (IrO₂) thin films were deposited on Si (100) substrates by means of pulsed laser deposition technique at various substrate (deposition) temperatures ranging from 250 to 500 °C. Effects of substrate temperature on the crystalline nature, morphology and electrical properties of the deposited films were analyzed by using X-ray diffraction, Raman spectroscopy, Scanning electron microscopy and four-point probe method. It was found that the above properties were strongly dependent on the substrate temperature. The as-deposited films at all substrate temperatures were polycrystalline tetragonal IrO₂ and the preferential growth orientation changed with the substrate temperature. IrO₂ films exhibited fairly homogeneous thickness and good adhesion with the substrate, the average feature size increases with the substrate temperature. The room-temperature resistivity of IrO₂ films decreased with the increase of substrate temperature and the minimum resistivity of (42 ± 6) μΩ cm was obtained at 500 °C. The resistivity of IrO₂ films correlated well with the corresponding film morphology changes.     

Preparation and study of thickness dependent electrical characteristics of zinc sulfide thin films

Zinc sulfide thin films have been deposited onto glass substrates by chemical bath deposition. The various deposition parameters such as volume of sulfide ion source, pH of bath, deposition time, temperature etc are optimized. Thin films of ZnS with different thicknesses of 76–332 nm were prepared by changing the deposition time from 6–20 h at 30° C temperature. The effect of film thickness on structural and electrical properties was studied. The electrical resistivity was decreased from 1.83 × 10⁵ Ω-cm to 0.363 × 10⁵ Ω-cm as film thickness decreased from 332 nm to 76 nm. The structural and activation energy studies support this decrease in the resistivity due to improvement in crystallinity of the films which would increase the charge carrier mobility and decrease in defect levels with increase in the thickness.     

Copper nitride films deposited by dc reactive magnetron sputtering

Copper nitride (Cu₃N) films were deposited on glass substrates by sputtering of copper target under various substrate temperatures in the range 303–523 K using dc reactive magnetron sputtering. The substrate temperature highly influenced the structural, mechanical, electrical and optical properties of the deposited films. The X-ray diffraction measurements showed that the films were of polycrystalline nature and exhibit preferred orientation of (111) phase of Cu₃N. The microhardness of the films increased from 2.7 to 4.4 GPa with the increase of substrate temperature from 303 to 473 K thereafter decreased to 4.1 GPa at higher temperature of 523 K. The electrical resistivity of the films decreased from 8.7 × 10⁻¹ to 1.1 × 10⁻³ Ωcm and the optical band gap decreased from 1.89 to 1.54 eV with the increase of substrate temperature from 303 to 523 K respectively.     

Electrical conduction and transmission electron microscopy studies of CdSe0.8Te0.2 thin films

Electrical resistance of CdSe_0.8Te_0.2 thin films were found to be dependent on various film parameters such as substrate temperature, film thickness, deposition rate and post-deposition heat treatment in different environments. A decrease in film resistivity was observed for thicker films and for those heat treated in vacuum. Films deposited at higher substrate temperatures and faster rates showed an increase in film resistivity. A spectrum of activation energies was observed in the films which fell within either of the activation energies observed in CdSe or CdTe films. Films heated in an oxygen environment showed an increase in film resistivity with a different activation energy. Transmission electron microscopy (TEM) of the films showed an improvement in crystallinity with increasing film thickness and substrate temperature, and a reduction in crystallinity with increasing deposition rate.     

Growth and characterization of high resistivity c-axis oriented ZnO films on different substrates by RF magnetron sputtering for MEMS applications

In the present work, we report the deposition of high resistivity c-axis oriented ZnO films by RF magnetron sputtering. The deposition parameters such as RF power, target-to-substrate spacing, substrate temperature, and sputtering gas composition affect the crystallographic properties of ZnO films, which were evaluated using XRD analysis. The self-heating of the substrate in plasma during film deposition was investigated and we report that highly “c-axis oriented” ZnO thin films can be prepared on different substrates without any external heating under optimized deposition parameters. The post-deposition annealing of the film at 900 °C for 1 h in air ambient increases the intensity of (002) peak corresponding to c-axis orientation in addition with the decrease in full width at half maxima (FWHM). Bond formation of ZnO was confirmed by FTIR analysis. Grains distribution and surface roughness have been analyzed using SEM and AFM. The DC resistivity of the films prepared under different deposition conditions was measured using MIS/MIM structures and was found to be in the range of 10¹¹–10¹² Ω cm at low electric field of 10⁴ V/cm. The ZnO film of 1 μm thickness has transmittance of over 85% in the visible region. Applications of these films in MEMS devices are discussed.     

Structural and magnetic studies of CTAC-assisted NiZn ferrite films by spray deposition

Spinel NiZn ferrite thin films were performed on polycarbonate glass substrates by spray deposited method at low temperature (<90 °C). After addition of cetyltrimethylammonium chloride(CTAC) made the adsorptive energy of substrate surface increase, smooth surface and uniform columnar film structures were obtained. The optimum reaction temperature up to 85 °C and the solution pH up to 7.5 were obtained. When the pH solution value increases from 6.5 to 7.5, the saturation magnetization accordingly increases to 2.48 × 10⁵ A/m and resistivity to 5.6 × 10² Ω cm. The high real permeability (μ′) of 36.1 and magnetic loss (μ″) of 53.2 for the ferrite film at 500 MHz were achieved. As the ferrite plate thickness is 1 mm, the attenuating characteristics for reflection loss ≤−10 dB can be obtained in the wide range between 0.5 GHz and 2.7 GHz.     

Effect of Thickness on the Properties of Ga-doped Nano-ZnO Thin Films Prepared by RF Magnetron Sputtering

Nano transparent conductive oxide (TCO) Ga-doped ZnO (GZO) thin films with thickness from 260 nm to 620 nm were prepared on glass substrates by RF magnetron sputtering from a powder target with 3 at.% Ga₂O₃. The substrate temperature was kept at 300 °C. The effect of thickness on the structural, electrical, and optical properties of GZO thin films was investigated. It shows that the nano-GZO films are dense and flat, and have polycrystalline structure with preferentially in the (002) orientation. With the increase of thickness, the crystallinity and the grain sizes of the films are improved, meanwhile the carrier concentration increases and the lowest resistivity of 3.685×10⁻³ Ω cm occurs in the 620 nm thick GZO film. The average optical transmittance of all the films is over 80% in the visible range. Decreasing the thickness, the optical transmission of the films increase, and the absorption edge shifts to shorter wavelength, which means the optical band gap is broadened.     

Grain growth of copper films prepared by chemical vapour deposition

Copper films having thickness 600 nm were prepared on TiN using chemical vapour deposition (CVD). The deposited films were annealed at various temperatures (350–550°C) in Ar and H₂(10%)-Ar ambients. The changes in the grain size of the films upon annealing were investigated. Annealing in an H₂(10%)-Ar ambient produced normal grain growth; annealing in an Ar ambient caused grain growth to stop at 550°C. The grain size followed a monomodal distribution and the mean size increased in proportion to the square root of the annealing time, indicating the curvature of the grain is the main driving force for grain growth. Upon annealing at 450°C for 30 min in an H₂(10%)-Ar ambient, the average grain size of the film increased from 122 nm to 219 nm, and the resistivity decreased from 2.35 μΩ cm to 2.12 μΩ cm at a film thickness of 600 nm. This revised version was published online in July 2006 with corrections to the Cover Date.     

ZnO thin films prepared by pulsed laser deposition

Zinc oxide (ZnO) thin films were deposited on soda lime glass substrates by pulsed laser deposition (PLD) in an oxygen-reactive atmosphere. The structural, optical, and electrical properties of the as-prepared thin films were studied in dependence of substrate temperature and oxygen pressure. High quality polycrystalline ZnO films with hexagonal wurtzite structure were deposited at substrate temperatures of 100 and 300 °C. The RMS roughness of the deposited oxide films was found to be in the range 2-9 nm and was only slightly dependent on substrate temperature and oxygen pressure. Electrical measurements indicated a decrease of film resistivity with the increase of substrate temperature and the decrease of oxygen pressure. The ZnO films exhibited high transmittance of 90% and their energy band gap and thickness were in the range 3.26-3.30 eV and 256-627 nm, respectively.     

Microstructural characteristics and mechanical properties of magnetron sputtered nanocrystalline TiN films on glass substrate

Nanocrystalline TiN thin films were deposited on glass substrate by d.c. magnetron sputtering. The microstructural characteristics of the thin films were characterized by XRD, FE-SEM and AFM. XRD analysis of the thin films, with increasing thickness, showed the (200) preferred orientation up to 1·26 μm thickness and then it transformed into (220) and (200) peaks with further increase in thickness up to 2·83 μm. The variation in preferred orientation was due to the competition between surface energy and strain energy during film growth. The deposited films were found to be very dense nanocrystalline film with less porosity as evident from their FE-SEM and AFM images. The surface roughness of the TiN films has increased slightly with the film thickness as observed from its AFM images. The mechanical properties of TiN films such as hardness and modulus of elasticity (E) were investigated by nanoindentation technique. The hardness of TiN thin film was found to be thickness dependent. The highest hardness value (24 GPa) was observed for the TiN thin films with less positive micro strain.     

Effect of microstructural evolution on magnetic properties of Ni thin films

The magnetic properties of Ni thin films, in the range 20–500 nm, at the crystalline-nanocrystalline interface are reported. The effect of thickness, substrate and substrate temperature has been studied. For the films deposited at ambient temperatures on borosilicate glass substrates, the crystallite size, coercive field and magnetization energy density first increase and achieve a maximum at a critical value of thickness and decrease thereafter. At a thickness of 50 nm, the films deposited at ambient temperature onto borosilicate glass, MgO and silicon do not exhibit long-range order but are magnetic as is evident from the non-zero coercive field and magnetization energy. Phase contrast microscopy revealed that the grain sizes increase from a value of 30–50 nm at ambient temperature to 120–150 nm at 503 K and remain approximately constant in this range up to 593 K. The existence of grain boundary walls of width 30–50 nm is demonstrated using phase contrast images. The grain boundary area also stagnates at higher substrate temperature. There is pronounced shape anisotropy as evidenced by the increased aspect ratio of the grains as a function of substrate temperature. Nickel thin films of 50 nm show the absence of long-range crystalline order at ambient temperature growth conditions and a preferred [111] orientation at higher substrate temperatures. Thin films are found to be thermally relaxed at elevated deposition temperature and having large compressive strain at ambient temperature. This transition from nanocrystalline to crystalline order causes a peak in the coercive field in the region of transition as a function of thickness and substrate temperature. The saturation magnetization on the other hand increases with increase in substrate temperature.     

Tungsten-doped ZnO transparent conducting films deposited by direct current magnetron sputtering

Highly conducting and transparent thin films of tungsten-doped ZnO (ZnO:W) were prepared on glass substrates by direct current (DC) magnetron sputtering at low temperature. The effect of film thickness on the structural, electrical and optical properties of ZnO:W films was investigated. All the deposited films are polycrystalline with a hexagonal structure and have a preferred orientation along the c-axis perpendicular to the substrate. The electrical resistivity first decreases with film thickness, and then increases with further increase in film thickness. The lowest resistivity achieved was 6.97 × 10⁻⁴ Ω cm for a thickness of 332 nm with a Hall mobility of 6.7 cm² V⁻¹ s⁻¹ and a carrier concentration of 1.35 × 10²¹ cm⁻³. However, the average transmittance of the films does not change much with an increase in film thickness, and all the deposited films show a high transmittance of approximately 90% in the visible range.     

Effect of substrate temperature on structural, optical and electrical properties of ZnO thin films deposited by pulsed laser deposition

ZnO thin films were grown by the pulse laser deposition (PLD) method using Si (100) substrates at various substrate temperatures. The influence of the substrate temperature on the structural, optical, and electrical properties of the ZnO thin films was investigated. All of the thin films showed c-axis growth perpendicular to the substrate surface. At a substrate temperature of 500 °C, the ZnO thin film showed the highest (002) peak with a full width at half maximum (FWHM) of 0.39°. The X-ray Photoelectron Spectroscopy (XPS) study showed that Zn was in excess irrespective of the substrate temperature and that the thin film had a nearly stoichiometrical composition at a substrate temperature of 500 °C. The photoluminescence (PL) investigation showed that the narrowest UV FWHM of 15.8 nm and the largest ratio of the UV peak to the deep-level peak of 32.9 were observed at 500 °C. Hall effect measurement systems provided information about the carrier concentration, mobility and resistivity. At a substrate temperature of 500 °C, the Hall mobility was the value of 37.4 cm²/Vs with carrier concentration of 1.36 × 10¹⁸ cm⁻³ and resistivity of 2.08 × 10⁻¹ Ω cm.     

Structure and conducting properties of La0.5Sr0.5CoO3−δ films on YSZ

La_0.5Sr_0.5CoO_3−δ (LSCO) thin films were deposited on yttria stabilized zirconia (YSZ) substrates by pulsed laser deposition (PLD) for application to thin film solid oxide fuel cell electrodes. During the deposition, the substrate temperature was varied from 450 to 750°C, and the oxygen pressure in the chamber was varied from 80 to 310 mTorr. Films deposited at 650°C and an oxygen background pressure of 150 mTorr were mostly (100) oriented. Deposition at higher temperatures or under lower oxygen pressures lead to mostly (110) oriented films. Films with low electrical resistivity of 10⁻³ Ω·cm were obtained.     

Effects of substrate temperature on the microstructure and photocatalytic reactivity of TiO2 films

Transmission electronic microscopy is used to study the structure, morphology and orientation of thin TiO2 films prepared by reactive magnetron sputtering on glass slides at different substrate temperatures (100 to 400 °C). The TiO2 films are used to purify a dye in waste water. The microstructure and photocatalytic reactivity of TiO2 films have been shown to be functions of deposition temperature. In the temperature range examined, all film samples have a porous nanostructure and the dimension of particles grown with increasing deposition temperature. Films are amorphous at temperatures of 100 °C and only anatase phase forms at 200 °C and above. Films deposited between 200 to 300 °C show a preferred orientation, while films at 400 °C change into complete random orientation. Deposition at 250 °C yields high efficiency in photocatalytic degradation owing to the high degree of preferred orientation and nanocrystalline/nanoporous anatase phase. © 1998 Kluwer Academic Publishers     

Structural,optical, and electrical properties of flash-evaporated copper indium diselenide thin films

Copper indium diselenide (CuInSe₂) compound was synthesized by reacting its elemental components, i.e., copper, indium, and selenium, in stoichiometric proportions (i.e., 1:1:2 with 5% excess selenium) in an evacuated quartz ampoule. Structural and compositional characterization of synthesized pulverized material confirms the polycrystalline nature of tetragonal phase and stoichiometry. CuInSe₂ thin films were deposited on soda lime glass substrates kept at different temperatures (300–573 K) using flash evaporation technique. The effect of substrate temperature on structural, morphological, optical, and electrical properties of CuInSe₂ thin films were investigated using X-ray diffraction analysis (XRD), atomic force microscopy (AFM), optical measurements (transmission and reflection), and Hall effect characterization techniques. XRD analysis revealed that CuInSe₂ thin films deposited above 473 K exhibit (112) preferred orientation of grains. Transmission and reflectance measurements analysis suggests that CuInSe₂ thin films deposited at different substrate temperatures have high absorption coefficient (~10⁴ cm⁻¹) and optical energy band gap in the range 0.93–1.02 eV. Results of electrical characterization showed that CuInSe₂ thin films deposited at different substrate temperatures have p-type conductivity and hole mobility value in the range 19–136 cm²/Vs. Variation of energy band gap and resistivity of CuInSe₂ thin films deposited at 523 K with thickness was also studied. The temperature dependence of electrical conductivity measurements showed that CuInSe₂ film deposited at 523 K has an activation energy of ~30 meV.     

Characterization of Tin disulphide thin films prepared at different substrate temperature using spray pyrolysis technique

Thin films of tin disulphide on glass substrates were prepared by spray pyrolysis technique using precursor solutions of SnCl₂·2H₂O and n–n dimethyl thiourea at different substrate temperatures varied in the range 348–423 K. Using the hot probe technique the type of conductivity is found to be n type. X ray diffraction analysis revealed the polycrystalline nature with increasing crystallinity with respect to substrate temperature. The preferential orientation growth of SnS₂ compound having hexagonal structure along (002) plane increased with the substrate temperature. The size of the tin disulphide crystallites with nano dimension were determined using the Full Width Half Maximum values of the Bragg peaks and found to increase with the substrate temperature. The surface morphology had been observed on the surface of these films using scanning electron microscope. The optical absorption and transmittance spectra have been recorded for these films in the wavelength range 400–800 nm. Thickness of these films was found using surface roughness profilometer. The absorption coefficient (α) was determined for all the films. Direct band gap values were found to exist in all the films deposited at different substrate temperatures. The value of room temperature resistivity in dark decreased from 5.95 × 10³ Ω cm for the amorphous film deposited at low temperature (348 K) to 2.22 × 10³ Ω cm for the polycrystalline film deposited at high temperature (423 K) whereas the resistivity values in light decreased from 1.48 × 10³ to 0.55 × 10³ Ω cm respectively, which is determined using the four probe method. Activation energy of these thin films was determined by Arrhenius plot.     

Optical and electrical properties of zinc oxide films prepared by spray pyrolysis

Zinc oxide thin films were prepared on glass substrates from an aqueous solution of zinc acetate by spray pyrolysis. These films were characterized using X-ray diffraction, scanning electron microscopy and optical transmission. The films were highly transparent to the visible radiation and electrically conductive. Films deposited at optimum conditions exhibited a resistivity of 3·15×10⁻³ Ωm along with a transmittance of 98% at 550 nm.