Influence of In doping on the structural,optical and acetone sensing properties of ZnO nanoparticulate thin films

Indium-doped zinc oxide (ZnO) nanoparticle thin films were deposited on cleaned glass substrates by spray pyrolysis technique using zinc acetate dihydrate [Zn(CH₃COO)₂ 2H₂O] as a host precursor and indium chloride (InCl₃) as a dopant precursor. X-ray diffraction results show that all films are polycrystalline zinc oxide having hexagonal wurtzite structure. Upon In doping, the films exhibit reduced crystallinity as compared with the undoped film. The optical studies reveal that the samples have an optical band gap in the range 3.23–3.27 eV. Unlike the undoped film, the In-doped films have been found to have the normal dispersion for the wavelength range 450–550 nm. Among all the films investigated, the 1 at% In-doped film shows the maximum response 96.8% to 100 ppm of acetone in air at the operating temperature of 300 °C. Even at a lower concentration of 25 ppm, the response to acetone in this film has been found to be more than 90% at 300 °C, which is attributed to the smaller crystallite size of the film, leading to sufficient adsorption of the atmospheric oxygen on the film surface at the operating temperature of 300 °C. Furthermore, In-doped films show the faster response and recovery at higher operating temperatures. A possible reaction mechanism of acetone sensing has been explained.     

Flexible organic light-emitting diodes on a polyestersulfone (PES) substrate using Al-doped ZnO anode grown by dual-plasma-enhanced metalorganic deposition system

This study proposes flexible organic light-emitting diodes (OLEDs) grown on polyestersulfone (PES) using Al-doped zinc oxide (AZO) as the anode, fabricated by the dual-plasma-enhanced chemical vapor deposition (DPEMOCVD) system. The experimental results including crystalline structure, optical, and electrical characteristics indicate that the quality of AZO films grown on PES depends on the deposition temperature and Al content. The optimal deposition temperature and Al content for AZO film are 185  C and 2.88 at%, respectively. Further increasing or decreasing the deposition temperature and Al content degrades the quality of AZO films. The optimal AZO film deposited on the PES substrate was used as the anode for flexible OLED. It shows a similar performance compared to OLEDs using commercial indium–tin-oxide (ITO) as the anode on glass, and represents enhanced characteristics to that of the commercial ITO anode on a flexible polyethylene naphthalate (PEN) substrate. This indicates that the DPEMOCVD-deposited AZO film on the PES substrate can be the anode for flexible OLEDs.     

Enhancement in the optical and electrical properties of CdS thin films through Ga and K co-doping

In the presented work, Ga-doped CdS and (Ga-K)-co-doped CdS thin films are grown on glass substrates at a temperature of 400 °C through spray pyrolysis. Influence of K-doping on structural, morphological, optical and electrical characteristics of CdS:Ga thin films are examined. K level is changed from 1 at% to 5 at% for CdS:Ga samples just as Ga concentration is fixed 2 at% for all CdS thin films. It is observed from the X-ray diffraction data that all the samples exhibit hexagonal structure and an increase level of K in Ga-doped CdS samples causes a degradation in the crystal quality. Energy-dispersive X-ray spectroscopy measurements illustrate that the best stoichiometric film is acquired when K content is 2 at% in Ga-doped CdS films. Optical transmission curves demonstrate that CdS:Ga thin films exhibit the best optical transparency in the visible range for 4 at% K content compared to other specimens. A widening in the optical bandgap is unveiled after K-dopings. It is obtained that maximum band gap value is found as 2.45 eV for 3 at%, 4 at% and 5 at%. K -dopings while Ga-doped CdS thin films display the band gap value of 2.43 eV. From photoluminescence measurements, the most intensified peak is observed in the deep level emission after incorporation of the 4 at% K atoms. As for electrical characterization results, the resistivity reduces and the carrier density improves with the increase of K concentration from 1 at% to 4 at%. Based on all the data, it can be deduced that 4 at% K-doped CdS:Ga thin films show the best optical and electrical behavior, which can be utilized for solar cell devices.     

Effect of doping concentration on the properties of bismuth doped tin sulfide thin films prepared by spray pyrolysis

Bismuth doped tin sulfide (SnS:Bi) thin films were deposited onto glass substrates by the spray pyrolysis technique at the substrate temperature of 350 °C. The effect of doping concentration [Bi/Sn] on their structural, optical and electrical properties was investigated as a function of bismuth doping between 0 and 8 at%. The XRD results showed that the films were polycrystalline SnS with orthorhombic structure and the crystallites in the films were oriented along (111) direction. Atomic force microscopy revealed that the particle size and surface roughness of the films increased due to Bi-doping. Optical analysis exhibited the band gap value of 1.40 eV for SnS:Bi (6 at%) which was lower than the band gap value for 0 at% of Bi (1.60 eV). The film has low resistivity of 4.788×10⁻¹ Ω-cm and higher carrier concentration of 3.625×10¹⁸ cm⁻³ was obtained at a doping ratio of 6 at%.     

Structural,morphological, electrical and optical studies of Cr doped SnO2 thin films deposited by the spray pyrolysis technique

Tin oxide (SnO₂) and chromium (Cr) doped tin oxide (Cr:SnO₂) thin films were deposited on the preheated glass substrates at 673 K by spray pyrolysis. Concentration of Cr was varied in the solution by adding chromium (III) chloride hexahydrate from 0 to 3 at%. The effect of Cr doping on the structural, electrical and optical properties of tin oxide films is reported. X-ray diffraction pattern confirms the tetragonal crystal structure for undoped and Cr doped tin oxide films. Scanning electron microscopic photographs show the modification of surface morphology of tin oxide film due to varying concentration of Cr. X-ray photoelectron spectra of Cr:SnO₂ (3 at%) thin film revealed the presence of carbon, tin, oxygen, and chromium. Carrier concentration and mobility of the SnO₂ films decrease with increasing concentration of Cr and 0.5 at% Cr doped tin oxide film acquires a mobility of 70 cm²/V s. Average optical transmittance in the 550–850 nm range varies from 38% to 47% with varying Cr concentration in the solution.     

Microstructure and electrical properties of nitrogen doped 3C–SiC thin films deposited using methyltrichlorosilane

The growth, microstructure and electrical properties of in-situ nitrogen doped 3C–SiC (111) thin films for sensor applications are presented in this paper. These thin films are deposited at a pressure of 2.5 mbar and temperature of 1040 °C on thermally oxidized Si (100) substrates from methyltrichlorosilane (MTS) precursor using a hot wall vertical low pressure chemical vapor deposition (LPCVD) reactor. Ammonia (NH₃) is used as the nitrogen doping gas. The sensor response depends on chemical composition, structure, morphology and operating temperature. The above properties are investigated for all in situ nitrogen doped (0, 9, 17 and 30 at% of nitrogen) 3C–SiC thin films using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM) and four probe method. The XRD patterns of the 3C–SiC thin films show a decrease in the crystallinity and intensity of the peak with increase in dopant concentration from 0 to 17 at%. AFM investigations show an improvement in the grain size of the nitrogen doped 3C–SiC thin films with increase in nitrogen concentration from 0 to 17 at%. The sheet resistance of nitrogen doped 3C–SiC thin films is measured by the four probe technique and it is found to decrease with increase in temperature in the range of 40–550 °C. The resistivity and average temperature coefficient of resistance (TCR) of doped 3C–SiC thin film deposited with 17 at% of nitrogen concentration are found to be 0.14 Ω cm and −103 ppm/°C, respectively and this can be used as a sensing material for high temperature applications.     

Electrical and thermal stability of Ag ohmic contacts for GaN-based flip-chip light-emitting diodes by using an AgAl alloy capping layer

We have investigated Ag(200 nm)/AgAl(100 nm) ohmic contacts to p-type GaN for near-UV (405 nm) flip-chip light-emitting diodes (LEDs). It is shown that the use of an AgAl alloy capping layer (with 8 at% Al) results in better electrical and optical properties as compared to single Ag contacts when annealed at 430 °C. For example, Ag/AgAl (8 at% Al) contacts give specific contact resistance of 4.6×10^–4 Ω cm² and reflectance of 90% at a wavelength of 405 nm. However, use of an AgAl (with 50 at% Al) layer is not effective. LEDs fabricated with the Ag/AgAl (8 at% Al) reflectors produce higher light output as compared with the ones with single Ag reflectors. Ohmic mechanisms of the Ag/AgAl (8 at% Al) contacts are described and discussed.     

Using the acetylacetonates of zinc and aluminium for the Metalorganic Chemical Vapour Deposition of aluminium doped zinc oxide films

Metalorganic Chemical Vapour Deposition is a promising method for the growth of thin aluminium doped zinc oxide films (ZnO:Al), a material with potential application as transparent conducting oxide (TCO), e.g. for the use as front electrode in solar cells. For the low-cost deposition, the choice of the precursors is extremely important. Here we present the deposition of quite homogeneous films from the acetylacetonates of zinc and aluminium that are rather cheap, commercially available and easy to handle. A user-made CVD-reactor activating the deposition process by the light of halogen lamps was used for film deposition. Well-ordered films with an aluminium content between 0 and 8% were grown on borosilicate glass and Si(100). On both types of substrate, the films are crystalline and show a preferred orientation along the (002)-direction. The 0.3 to 0.5 μm thick films are highly transparent in the visible region. The best films show a low electric resistivity between 2.4 and 8 mΩ cm.     

Enhanced short circuit current density of dye-sensitized solar cells aided by Sr,V co-doped TiO2 particles

This study comes up with a straightforward method for preparing uniform electrodes containing Sr,V co-doped TiO₂ particles for dye-sensitized solar cells (DSCs) applications. The spherical particles with the average diameter around 2.5 µm are assembled from small nanoparticles with the average grain size of 60 nm. X-ray diffraction (XRD) reveals that the introduction of dopants not only inhibits the growth of rutile phase, but also results in smaller primary crystallites, improving the surface area and dye adsorption ability of the electrodes. X-ray photoelectron spectroscopy (XPS) showed that Sr²⁺ and V⁵⁺ ions are well incorporated into the titania crystal lattice without forming specific Strontium and Vanadium compositions. UV–visible spectra show that the co-doped TiO₂ films have lower band gap energy than that of undoped-TiO₂, extending the absorption of TiO₂ into visible region. Isolated energy levels in band structure of TiO₂ as well as local lattice distortions due to dopants introduction are the parameters enhanced the short circuit current density of the cells. The TiO₂ DSC co-doped with 0.075 at% Sr and 1.5 at% V (i.e., S7V15 cell) had the highest circuit current density and power conversion efficiency of 18.57 and 7.76%, respectively, as a result of less recombination, which is demonstrated by electrochemical impedance spectroscopy (EIS).     

Tuning optical,electrical and magnetic properties of fiber structured ZnO film by deposition temperature and precursor concentration

Highly transparent ZnO films were deposited on glass substrates using zinc acetate solution through cost effective spray pyrolysis method. A comprehensive study was carried out to understand the effects of deposition temperature and precursor concentrations on structure, surface morphology, optical, electrical and magnetic properties of the deposited films. All deposited films were polycrystalline in nature with hexagonal wurtzite structure. The films were preferentially oriented along (1 0 1) plane up to 723 K beyond which orientation changed to (0 0 2) plane. Irrespective of precursor concentration used, the films deposited at 673 K and 723 K showed fibrous structure. The films deposited at higher temperature led to enhanced transmittance and optical energy band gap. With higher precursor concentrations the transmittance decreased while the band gap increased. Photoluminescence studies revealed the presence of various defects leading to emission in the visible region apart from band to band transition near UV region. Lowest electrical resistivity was obtained for films deposited at 723 K which is of the order 10² Ω cm. At room temperature, all deposited films were diamagnetic while they were paramagnetic at 5 K.     

Morphology,optical and AC electrical properties of nanostructure thin film of bromo indium phthalocyanine

Sandwich devices of bromo indium phthalocyanine (BrlnPc) thin films with aluminium electrodes were deposited on polyborosilicate substrate, using electron beam gun evaporation technique at room temperature. The AC electrical properties of nanostructure thin films (Al/BrInPc/Al) were examined in the temperature range of 303–393 K and frequency (f) between 10² and 10⁵ Hz. Structural and optical behaviour of samples were investigated by scanning electron microscope (SEM) images, X-ray diffraction (XRD) micrograph and optical absorption. Capacitance increase with increasing temperature for frequencies <10³ Hz and is almost independent of temperature for the range of frequencies >10³ Hz. Dissipation factor decrease with increasing frequency to a minimum value and increased noticeably thereafter. The AC electrical properties of nanostructured thin films of our materials are in agreement with the model of Goswami and Goswami. The band theory and hopping mechanism are applicable in explaining the conduction process for the frequency range of f<10³ Hz and f>10³ Hz, respectively.     

Growth of Zn doped Cu(In, Ga)Se2 thin films by RF sputtering for solar cell applications

Cu(In, Ga)Se₂ (CIGS) surface was modified with Zn doping using a magnetron sputtering method. CuInGa:Zn precursor films targeting a CuIn_0.7Ga_0.3Se₂ stoichiometry with increasing Zn content from 0 to 0.8 at% were prepared onto Mo-coated glass substrates via co-sputtering of Cu–Ga alloy, In and Zn targets. The CuInGa:Zn precursors were then selenized with solid Se pellets. The structures and morphologies of grown Zn doped CIGS films were found to depend on the Zn content. At zinc doping level ranging between 0.2 and 0.6 at%, the Zn doping improved the crystallinity and surface morphology of CIGS films. Compared with the performance of the non-doped CIGS cell, the fabricated CIGS solar cell displayed a relative efficiency enhancement of 9–22% and the maximum enhancement was obtained at a Zn content of 0.4 at%.     

Deposition and characterization of pure and Cd doped SnO2 thin films by the nebulizer spray pyrolysis (NSP) technique

Pure and cadmium doped tin oxide thin films were deposited on glass substrates from aqueous solution of cadmium acetate, tin (IV) chloride and sodium hydroxide by the nebulizer spray pyrolysis (NSP) technique. X-ray diffraction reveals that all films have tetragonal crystalline structure with preferential orientation along (200) plane. On application of the Scherrer formula, it is found that the maximum size of grains is 67 nm. Scanning electron microscopy shows that the grains are of rod and spherical in shape. Energy dispersive X-ray analysis reveals the average ratio of the atomic percentage of pure and Cd doped SnO₂ films. The electrical resistivity is found to be 10² Ω cm at higher temperature (170 °C) and 10³ Ω cm at lower temperature (30 °C). Optical band gap energy was determined from transmittance and absorbance data obtained from UV–vis spectra. Optical studies reveal that the band gap energy decreases from 3.90 eV to 3.52 eV due to the addition of Cd as dopant with different concentrations.     

Magneto-optical characteristics of Mn-doped ZnO films deposited by ultrasonic spray pyrolysis

This work considers a Mn-doped ZnO (ZnO:Mn) film deposited on a slide glass substrate by ultrasonic spray pyrolysis. ZnO:Mn (Mn at 1.5 at%) film with and without an applied magnetic field, is demonstrated to have absorption edges at 2.74 and 2.84 eV, respectively. These values are lower than that of a pure ZnO film because the Mn-doping causes the exchange of s–d and p–d interactions or high carrier concentration. When the ZnO:Mn film is placed in a magnetic field B_z of 0.5 T, an absorption edge and a photoluminescence (PL) shift of about 0.1 eV and 85 meV, respectively, are observed. This shift is attributed to the interband magneto-optic absorption associated with the Landau splitting. The observed shift increases with the amount of Mn dopant.     

Investigation of aluminum and gallium co-doped ZnO powders and their effects on the properties of targets

Aluminum and gallium co-doped ZnO (AGZ) powders were synthesized by the chemical co-precipitation method with the same Al doping concentration (3 at%) and different Ga doping concentrations (0–0.5 at%). The microstructure, lattice distortion and surface morphology of AGZ powders were investigated because the properties of targets were related to corresponding powders. Both AZO and AGZ targets were prepared by molding and atmospheric pressure sintering. The microstructure, morphologies, electrical properties and densification of sintered targets were also studied. The measured results showed that the grain sizes of AGZ powders are smaller than AZO powder, the former has a larger specific area, and the distribution of AGZ particles are more homogeneous, which are good for preparation of a high-density target. Besides, the extent of ZnO lattice distortion exhibits a downward trend with the increase of the Ga doping concentration. The AGZ target with appropriate concentration of Ga (0.3 at%) has the lowest resistivity of 2.518×10⁻³ Ω cm and the highest relative density of 99.2%. In general, the moderate Al–Ga co-doping proportion leads to finer grain size, lower resistivity, higher Hall mobility and higher sintered density.     

Effect of fluorine doping on the structural,optical and electrical properties of spray deposited cadmium stannate thin films

Cadmium stannate (Cd₂SnO₄) thin films were coated on Corning 1737 glass substrates at 540 °C by spray pyrolysis technique, from the aqueous solution of cadmium acetate and tin (II) chloride precursors. Fluorine doped Cd₂SnO₄ (F: Cd₂SnO₄) thin films were prepared by adding ammonium fluoride in the range of 0–5 wt% of the total weight of cadmium acetate and tin (II) chloride in the spray solution. Thickness of the prepared films is about 300 nm. X-ray diffraction analysis of the Cd₂SnO₄ and 3 wt% F: Cd₂SnO₄ films shows the signature for the growth along (222) direction. Scanning electron micrographs showed that fluorine doping effectively modifies the surface morphology of Cd₂SnO₄ films. Average optical transmittance in the visible region (500–850 nm) for Cd₂SnO₄ is ~79% and it is increased to ~83% for 1 wt% doping concentration of the NH₄F in the solution. Fluorescence spectra of F: Cd₂SnO₄ (1 wt% and 3 wt%) exhibit peak at 601 nm. F: Cd₂SnO₄ film (1 wt%) shows mobility of ~42 cm²/V s, carrier concentration of ~9.5×10¹⁹ cm^?3 and resistivity of ~1.5×10^?3 Ω cm.     

ZnO thin Films with blue emission grown using chemical spray pyrolysis

Photoluminescence in the characteristic blue-green region of the spectrum was emitted by zinc oxide (ZnO) thin films grown by chemical spray pyrolysis. We have been able to optimize spray rate and substrate temperature to obtain ZnO thin films with emission centered at ～383 nm and ～517 nm, respectively. We also observed that Al-doped ZnO films resulted in improved radiative efficiency of the near-band-edge emission; optimized Al-doped spray deposited thin films emitted only blue light.     

Synthesis of ZnO nanostructure films by thermal evaporation approach and their application in dye-sensitized solar cells

Zinc oxide (ZnO) films were prepared successfully by simple thermal evaporation of zinc acetate dihydrate at low temperature onto FTO (fluorine-doped tin oxide) glass substrates coated with thin ZnO seed layer. The synthetic parameter such as temperature was found to determine the morphology of nanostructures. ZnO nanorod (NR) and nanoparticle (NP) films have been synthesized at 245 and 350 °C, respectively, for 6 h. The dye-sensitized solar cells (DSSCs) were fabricated using the ZnO nanostructure films as photosensitized electrodes. A maximum photoelectric conversion efficiency (PCE) of 1.56%, and short-circuit photocurrent density of 5.12 mA/cm² were achieved with the ZnO NP-based DSSC. The PCE increase was ascribed to the reduced recombination loss and prolonged electron lifetime according to electrochemical impedance spectroscopy (EIS).     

Compact Brillouin bismuth–gallium–aluminum co-doped erbium doped fiber laser

A single-wavelength Brillouin–erbium fiber laser (BEFL) is demonstrated using high germanium dopant concentration fiber and bismuth–gallium–aluminum co-doped high concentration erbium doped fiber (EDF). A 20-m long high Ge-doped fiber is used to provide nonlinear gains to generate a stimulated Brillouin scattering (SBS), and a 4.3-m long Bi–Ga–Al EDF provides linear gains to amplify the SBS. The relationship between the fiber parameters (dopant concentration, effective area, length and so on) of both linear and nonlinear medium and the output performance was discussed. The BEFL power increases as the effective area of the high Ge-doped fiber decreases. There is an optimum length in the high Ge-doped fiber which is 20-m long in this paper. The BEFL output power also increases as the output power of the Bi–Ga–Al EDF increases. The output performance increases as the erbium doping concentration increases. It is necessary to get the effective area of the Bi–Ga–Al EDF large enough to decrease the fiber loss. The optimum length in the Bi–Ga–Al EDF is 4.3 m. The BEFL operates at 1563.61 nm, which is upshifted by 0.09 nm from the Brillouin pump (BP). It has a peak power of ?3 dBm and a side-mode suppression ratio of 26 dB. The BP wavelength is tunable within a wavelength range from 1562.5 to 1564 nm. The BEFL has a narrow linewidth. It is suitable for many potential applications, such as optical communication and sensors.     

Highly efficient two component phosphorescent organic light-emitting diodes based on direct hole injection into dopant and gradient doping

A series of two component phosphorescent organic light-emitting diodes (PHOLEDs) combing the direct hole injection into dopant strategy with a gradient doping profile were demonstrated. The dopant, host, as well as molybdenum oxide (MoO₃)-modified indium tin oxide (ITO) anode were investigated. It is found that the devices ITO/MoO₃ (0 or 1 nm)/fac-tris(2-phenylpyridine)iridium [Ir(ppy)₃]:1,3,5-tris(N-phenylbenzimidazole-2-yl)benzene (TPBi) (30 → 0 wt%, 105 nm)/LiF (1 nm)/Al (100 nm) show maximum external quantum efficiency (EQE) over 20%, which are comparable to multi-layered PHOLEDs. Moreover, the systematic variation of the host from TPBi to 4,7-diphenyl-1,10-phenanthroline (Bphen), dopant from Ir(ppy)₃ to bis(2-phenylpyridine)(acetylacetonate)iridium [Ir(ppy)₂(acac)], and anodes between ITO and ITO/MoO₃ indicates that balancing the charge as well as controlling the charge recombination zone play critical roles in the design of highly efficient two component PHOLEDs.