Influence of growth time on crystalline structure,conductivity and optical properties of ZnO thin films

This paper examines the growth of ZnO thin films on glass substrate at 350℃using an ultrasonic spray technique.We have investigated the influence of growth time ranging from 1 to 4 min on structural,optical and electrical properties of ZnO thin films.The as-grown films exhibit a hexagonal structure wurtzite and are(002) oriented.The maximum value of grain size G = 63.99 nm is attained for ZnO films grown at 2 min.The average transmittance is about 80%,thus the films are transparent in the visible region.The optical gap energy is found to increase from 3.26 to 3.37 eV with growth time increased from 1 to 2 min.The minimum value of electrical resistivity of the films is 0.13Ω·cm obtained at 2 min.A systematic study on the influence of growth time on the properties of ZnO thin films deposited by ultrasonic spray at 350℃has been reported.     

Effect of electrode materials and annealing on metal-semiconductor contact of Ga2O3 with metal

Gallium oxide(Ga2O3) thin films were prepared on Si substrate by magnetron sputtering. The obtained samples were comprehensively characterized by X-ray photoelectron spectroscopy(XPS) and scanning electron microscope(SEM). Ti, Pt, Ni and AZO were deposited on the Ga2O3 thin films as electrodes. This paper mainly studies the metal-semiconductor contact formed by these four materials on the films and the influence of annealing at 500℃ on the metal-semiconductor contact. The I-V characteristics show a good linear relationship, which indicates ohmic contact between Ga2O3 and other electrodes.     

The effect of the film thickness and doping content of SnO2:F thin films prepared by the ultrasonic spray method

This paper reports on the effects of film thickness and doping content on the optical and electrical properties of fluorine-doped tin oxide. Tin(II) chloride dehydrate, ammonium fluoride dehydrate, ethanol and HCl were used as the starting materials, dopant source, solvent and stabilizer, respectively. The doped films were deposited on a glass substrate at different concentrations varying between 0 and 5 wt% using an ultrasonic spray technique. The SnO2 :F thin films were deposited at a 350 C pending time(5, 15, 60 and 90 s). The average transmission was about 80%, and the films were thus transparent in the visible region. The optical energy gap of the doped films with 2.5 wt% F was found to increase from 3.47 to 3.89 eV with increasing film thickness, and increased after doping at 5 wt%. The decrease in the Urbach energy of the SnO2:F thin films indicated a decrease in the defects. The increase in the electrical conductivity of the films reached maximum values of 278.9 and 281.9( cm)1for 2.5 and 5 wt% F, respectively, indicating that the films exhibited an n-type semiconducting nature. A systematic study on the influence of film thickness and doping content on the properties of SnO2:F thin films deposited by ultrasonic spray was reported.     

Effect of deposition conditions on the physical properties of Sn_xS_y thin films prepared by the spray pyrolysis technique

Tin sulfide thin films（Sn_xS_y） with an atomic ratio of y/x = 0.5 have been deposited on a glass substrate by spray pyrolysis.The effects of deposition parameters,such as spray solution rate（R）,substrate temperature （T_s） and film thickness（t）,on the structural,optical,thermo-electrical and photoconductivity related properties of the films have been studied.The precursor solution was prepared by dissolving tin chloride（SnCl₄,5H₂O） and thiourea in propanol,and Sn_xS_y thin film was prepared with a mole ratio of y/x = 0.5.The prepared films were characterized by X-ray diffraction（XRD）,scanning electron microscopy（SEM） and UV-vis spectroscopy. It is indicated that the XRD patterns of Sn_xS_y films have amorphous and polycrystalline structures and the size of the grains has been changed from 7 to 16 nm.The optical gap of Sn_xS_y thin films is determined to be about 2.41 to 3.08 eV by a plot of the variation of（αhv）² versus hv related to the change of deposition conditions.The thermoelectric and photo-conductivity measurement results for the films show that these properties are depend considerably on the deposition parameters.     

Flexible magnetic thin films and devices

Flexible electronic devices are highly attractive for a variety of applications such as flexible circuit boards,solar cells,paper-like displays,and sensitive skin,due to their stretchable,biocompatible,light-weight,portable,and low cost properties.Due to magnetic devices being important parts of electronic devices,it is essential to study the magnetic properties of magnetic thin films and devices fabricated on flexible substrates.In this review,we mainly introduce the recent progress in flexible magnetic thin films and devices,including the study on the stress-dependent magnetic properties of magnetic thin films and devices,and controlling the properties of flexible magnetic films by stress-related multi-fields,and the design and fabrication of flexible magnetic devices.     

Growth-temperature-dependent optical and acetone detection properties of ZnO thin films

Zinc oxide (ZnO) thin films were prepared onto glass substrates at moderately low growth temperature by two-stage spray pyrolysis technique. The effects of growth temperature on structural, optical and acetone detection properties were investigated with X-ray diffractometry, a UV-visible spectrophotometer, photoluminescence (PL) spectroscopy and a homemade gas sensor testing unit, respectively. All the films are polycrystalline with a hexagonal wurtzite phase and exhibit a preferential orientation along [002] direction. The film crystallinity is gradually enhanced with an increase in growth temperature. The optical measurements show that all the films are physically highly transparent with a transmittance greater than 82% in the visible range. The band gap of the film is observed to exhibit a slight red shift with an increasing growth temperature. The PL studies on the films show UV/violet PL band at ～ 395 nm. Among all the films investigated, the film deposited at 250 ℃ demonstrates a maximum sensitivity of 13% towards 20 ppm of acetone vapors at 300 ℃ operating temperature.     

The calculation of band gap energy in zinc oxide films

We investigated the optical properties of undoped zinc oxide thin films as the n-type semiconductor; the thin films were deposited at different precursor molarities by ultrasonic spray and spray pyrolysis techniques. The thin films were deposited at different substrate temperatures ranging between 200 and 500 ℃. In this paper, we present a new approach to control the optical gap energy of ZnO thin films by concentration of the ZnO solution and substrate temperatures in a cost-effective way. The model proposed to calculate the band gap energy with the Urbach energy was investigated. The relation between the experimental data and theoretical calculation suggests that the band gap energies are predominantly estimated by the Urbach energies, film transparency, and concentration of the ZnO solution and substrate temperatures. The measurements by these proposal models are in qualitative agreements with the experimental data; the correlation coefficient values were varied in the range 0.96-0.99999, indicating high quality representation of data based on Equation (2), so that the relative errors of all calculation are smaller than 4%. Thus, one can suppose that the undoped ZnO thin films are chemically purer and have many fewer defects and less disorder owing to an almost complete chemical decomposition and contained higher optical band gap energy.     

Effect of Fe-doping on the structural and optical properties of ZnO thin films prepared by spray pyrolysis

Fe-doped ZnO thin films have been prepared by spray pyrolysis on glass substrates and the influence of Fe-doping concentration on the structural and optical properties of the films has been studied.The X-ray diffraction (XRD) analysis shows that Fe doping has a significant effect on crystalline quality,grain size and strain in the thin films.The best crystalline structure is obtained for 3 at%Fe doping as observed from scanning electron microscopy (SEM) and XRD.However,lower or higher Fe-doping degrades the crystalline quality in turn.Moreover,UV spectroscopy demonstrates the influence of Fe-incorporation on visible range transmittance of ZnO where the best transmittance is obtained for 3 at%doping.The results have been illustrated simultaneously focusing previous results obtained from literature.     

Low substrate temperature deposition of transparent and conducting ZnO: Al thin films by RF magnetron sputtering

Transparent and conducting Al-doped ZnO(ZnO:Al) films were prepared on glass substrate using the RF sputtering method at different substrate temperatures from room temperature(RT) to 200 ℃. The structural,morphological, electrical and optical properties of these films were investigated using a variety of characterization techniques such as low angle XRD, Raman spectroscopy, X-ray photoelectron spectroscopy(XPS), field-emission scanning electron microscopy(FE-SEM), Hall measurement and UV–visible spectroscopy. The electrical properties showed that films deposited at RT have the lowest resistivity and it increases with an increase in the substrate temperature whereas carrier mobility and concentration decrease with an increase in substrate temperature. Low angle XRD and Raman spectroscopy analysis reavealed that films are highly crystalline with a hexagonal wurtzite structure and a preferred orientation along the c-axis. The FE-SEM analysis showed that the surface morphology of films is strongly dependent on the substrate temperature. The band gap decreases from 3.36 to 3.29 e V as the substrate temperature is increased from RT to 200 ℃. The fundamental absorption edge in the UV region shifts towards a longer wavelength with an increase in substrate temperature and be attributed to the Burstein-Moss shift. The synthesized films showed an average transmission(> 85%) in the visible region, which signifies that synthesized ZnO:Al films can be suitable for display devices and solar cells as transparent electrodes.     

Cadmium sulfide thin films growth by chemical bath deposition

Cadmium sulfide (CdS) thin films have been prepared by a simple technique such as chemical bath deposition (CBD).A set of samples CdS were deposited on glass substrates by varying the bath temperature from 55 to 75 ℃ at fixed deposition time (25 min) in order to investigate the effect of deposition temperature on CdS films physical properties.The determination of growth activation energy suggests that at low temperature CdS film growth is governed by the release of Cd2+ ions in the solution.The structural characterization indicated that the CdS films structure is cubic or hexagonal with preferential orientation along the direction (111) or (002),respectively.The optical characterization indicated that the films have a fairly high transparency,which varies between 55％ and 80％ in the visible range of the optical spectrum,the refractive index varies from 1.85 to 2.5 and the optical gap value of which can reach 2.2 eV.It can be suggested that these properties make these films perfectly suitable for their use as window film in thin films based solar cells.     

Giant modulation of magnetism in(Ga,Mn)As ultrathin films via electric field

Taking the advantages of semiconducting properties and carrier-mediated ferromagnetism in(Ga,Mn)As,a giant modulation of magnetism via electric field in(Ga,Mn)As ultrathin film has been demonstrated.Specifically,huge interfacial electric field is obtained by using ionic liquid as the gate dielectric.Both magnetization and transport measurements are employed to characterize the samples,while the transport data are used to analyze the electric filed effect on magnetism.Complete demagnetization of(Ga,Mn)As film is then realized by thinning its thickness down to ~2 nm,during which the degradation of ferromagnetism of(Ga,Mn)As ultrathin film induced by quantum confinement effect is suppressed by inserting a heavily-doped p-type GaAs buffer layer.The variation of the Curie temperature is more than 100 K,which is nearly 5-times larger than previous results.Our results provide a new pathway on the efficient electrical control of magnetism.     

Microstructure and optoelectronic properties of gallium- titanium-zinc oxide thin films deposited by magnetron sputtering

Gallium-titanium-zinc oxide(GTZO) transparent conducting oxide(TCO) thin films were deposited on glass substrates by radio frequency magnetron sputtering. The dependences of the microstructure and optoelectronic properties of GTZO thin films on Ar gas pressure were observed. The X-ray diffraction(XRD) and scanning electron microscopy(SEM) results 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. With the increment of Ar gas pressure, the microstructure and optoelectronic properties of GTZO thin films will be changed. When Ar gas pressure is 0.4 Pa, the deposited films possess the best crystal quality and optoelectronic properties.     

Structural Characteristic of CdS Thin films and Their Influence on Cu(in,Ga)Se2(CIGS) Thin Film Solar Cell

Deposition and structural characteristics of cadmium sulfide (CdS) thin films by chemical bath deposition (CBD) technique from a bath containing thiourea,cadmium acetate,ammonium acetate and ammonia in an aqueous solution are reported.Researches are made on the influence of the fundamental parameters including pH,temperature，and concentrations of the solution involved in the chemical bath deposition of CdS and titration or dumping of the thiourea solution on the structure characteristic of CdS thin films.The pH of the solution plays a vital role on the characteristic of the CdS thin films.The XRD patterns show that the change in the pH of the solution results in the change in crystal phase from predominant hexagonal phase to predominant cubic phase.The CdS thin films with the two different crystal phases have different influences on CIGS thin film solar cells.The crystal mismatch and the interface state density of the cCdS(cubic phase CdS) and CIGS are about 1.419% and 8.507×1e12cm－２ respectively,and those of the h-CdS(hexagonal phase CdS) and CIGS are about 32.297% and 2.792×1e12cm－２ respectively.It is necessary for high efficiency CIGS thin film solar cells to deposit the cubic phase CdS thin films.     

Investigation of post-thermal annealing on material properties of Cu-In-Zn-Se thin films

The Cu-In-Zn-Se thin film was synthesized by changing the contribution of In in chalcopyrite CuInSe2 with Zn.The XRD spectra of the films showed the characteristic diffraction peaks in a good agreement with the quaternary Cu-In-Zn-Se compound.They were in the polycrystalline nature without any post-thermal process,and the main orientation was found to be in the (112) direction with tetragonal crystalline structure.With increasing annealing temperature,the peak intensities in preferred orientation became more pronounced and grain sizes were in increasing behavior from 6.0 to 25.0 nm.The samples had almost the same atomic composition of Cu0.5In0.5ZnSe2.However,EDS results of the deposited films indicated that there was Se re-evaporation and/or segregation with the annealing in the structure of the film.According to the optical analysis,the transmittance values of the films increased with the annealing temperature.The absorption coefficient of the films was calculated as around 105 cm-1 in the visible region.Moreover,optical band gap values were found to be changing in between 2.12 and 2.28 eV depending on annealing temperature.The temperature-dependent dark-and photo-conductivity measurements were carried out to investigate the electrical characteristics of the films.     

Magnetic interference gonioapparent thin film based on metal-dielectric-metal structure for optical security devices

In recent years, magnetic interference thin films have gained wide attention in optical security devices field by virtue of their gonioapparent and dynamic 3D effects. Based on the color mechanism of metal-dielectric Fabry-Perot structure, a novel seven-layer magnetic thin film structure is proposed by adopting the ultrathin metal layer as a bonding layer and a pure metallic Ni layer as a magnetic layer as well as a reflective layer. Color target optimization optimac method is utilized that realizes the seven-layer metal-dielectric optically variable magnetic thin film structure with green at the normal incidence and purple-red at 60°. The structure effectively solves the delaminate problem and simplifies the multilayer structure. Through different combined magnetic field designs, the magnetic orientation experiment of the prepared magnetic optically variable thin film is carried out, and the 3 D anti-counterfeiting with remarkable dynamic color change effect is obtained, which provides a new solution for optical security devices.     

Research on the properties of ZnO1-xSx thin films modified by sulfur doping for CIGS solar cells

ZnO1-xSx thin films modified by sulfur doping were prepared on glass substrates by chemical bath deposition (CBD) for studying the effect of thiourea concentration on the thin film properties. The obtained ZnO1-xSx thin films were characterized by scanning electron microscopy (SEM), which shows the surfaces of ZnO1-xSx thin films deposited under the thiourea concentration of 0.14 M are more compact. X-ray diffraction (XRD) measurement shows that the ZnO1-xSx thin films with hexagonal crystal structure had strong diffraction peaks and better crystallinity. The optical transmittance of the ZnO1-xSx thin films with 0.14 M thiourea concentration is above 80% in the wavelength range of 300—900 nm. According to the measurement results from spectrophotometer, the ZnO1-xSx band gap energy value Eg varies nonlinearly with different S/(S+O) ratio x, and increases with the increase of x. There is a band gap value of 2.97 eV in the ZnO1-xSx thin films deposited under 0.14 M thiourea concentration. Therefore, the thin films have better structural, optical and electric properties, and are more suitable for the buffer layers of copper indium gallium selenide (CIGS) thin film solar cells.     

Formaldehyde OTFT Sensors Based on Airbrushed Different Ratios of P3HT/ZnO Films

The formaldehyde(HCHO) detecting at room temperature is of great significance.Different ratios of P3HT/ZnO composite films(3:1,1:1,and 1:3) were deposited on the organic thin film transistor(OTFT) by spray-deposition technology,and the electrical properties and HCHO-sensing properties of all the prepared OTFT devices were measured by Keithley 4200-SCS source measurement unit.The results show that the OTFT sensor based on the P3HT/ZnO films with the ratio of 1:1 exhibited the best output and transfer curves.Different changing tendency were observed with the increase of ZnO proportion when exposed to HCHO at room temperature,and the device with the ratio of 1:1 behaved a good response and recovery characteristics.     

Physical properties of hematite -Fe2O3 thin films: Application to photoelectrochemical solar cells

The physical properties and photoelectrochemical characterization of aluminium doped hematite -Fe2O3, synthesized by spray pyrolysis, have been investigated in regard to solar energy conversion. Stable Al-doped iron (III) oxide thin films synthesized by spray pyrolysis technique reveals an oxygen deficiency and the oxide exhibits n-type conductivity confirmed by anodic photocurrent generation. The preparative parameters have been optimized to obtain good quality thin films which are uniform and well adherent to the substrate. The deposited iron oxide thin films shows the single hematite phase with polycrystalline rhombohedral crystal structure with crystallite size 20-40 nm. Optical analysis enabled to point out the increase in direct band-gap energy from 2.2 to 2.25 eV with doping concentration which is attributed to blue shift. The dielectric constant and dielectric loss are studied as a function of frequency. To understand the conduction mechanism in the films AC conductivity is measured. The conduction occurs by small polaron hopping through mixed valences Fe2+/3+ with an electron mobility 300K of 1.08 Vcm2s-1. The -Fe2O3 exhibits long term chemical stability in neutral solution and has been characterized photoelectrochemically to assess its activity as a photoanode for various electrolytes using white light to obtain I–V characteristics. The Al-doped hematite exhibited higher photocurrent response when compared with undoped films achieving power conversion efficiency of 2.37% at 10 at% Al:Fe2O3 ¬ thin films along with fill factor 0.38 in NaOH electrolyte. The flat band potential Vfb (-0.87 VSCE) is determined by extrapolating the linear part to C-2 = 0 and the slope of the Mott-Schottky plot.     

Structural and optical properties of polycrystalline CdS thin films deposited by electron beam evaporation

Highly crystalline and transparent cadmium sulphide(CdS) films were deposited on glass substrate by electron beam evaporation technique.The structural and optical properties of the films were investigated.The X-ray diffraction analysis revealed that the CdS films have a hexagonal structure and exhibit preferred orientation along the(002) plane.Meanwhile,the crystalline quality of samples increased first and then decreased as the substrate temperature improved,which is attributed to the variation in film thickness.UV-vis spectra of CdS films indicate that the absorption edge becomes steeper and the band gap present fluctuation changes in the range of 2.389-2.448 eV as the substrate temperature increased.The photoluminescence peak of the CdS films was found to be broadened seriously and there only emerges a red emission band at 1.60 eV.The above results were analyzed and discussed.     

Cubic AlN thin film formation on quartz substrate by pulse laser deposition

Cubic AlN thin films were obtained on quartz substrate by pulse laser deposition in a nitrogen reactive atmosphere. A Nd-YAG laser with a wavelength of 1064 nm was used as the laser source. In order to study the influence of the process parameters on the deposited AlN film, the experiments were performed at various technique parameters of laser energy density from 70 to 260 J/cm², substrate temperature from room temperature to 800℃ and nitrogen pressure from 0.1 to 50 Pa. X-ray diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy were applied to characterize the structure and surface morphology of the deposited AlN films. It was found that the structure of AlN films deposited in a vacuum is rocksalt under the condition of substrate temperature 600-800℃, nitrogen pressure 10-0.1 Pa and a moderate laser energy density (190 J/cm²). The high quality AlN film exhibited good optical property.