Fabrication of Ag nanoparticle/ZnO thin films using dual-plasma-enhanced metal-organic chemical vapor deposition (DPEMOCVD) system incorporated with photoreduction method and its application

We report a novel method to grow silver nanoparticle/zinc oxide (Ag NP/ZnO) thin films using a dual-plasma-enhanced metal-organic chemical vapor deposition (DPEMOCVD) system incorporated with a photoreduction method. The crystalline quality, optical properties, and electrical characteristics of Ag NP/ZnO thin films depend on the AgNO₃ concentration or Ag content and annealing temperature. Optimal Ag NP/ZnO thin films have been grown with a AgNO₃ concentration of 0.12 M or 2.54 at%- Ag content and 500 °C- rapid thermal annealing (RTA); these films show orientation peaks of hexagonal-wurtzite-structured ZnO (002) and face-center-cubic-crystalline Ag (111), respectively. The transmittance and resistivity for optimal Ag NP/ZnO thin films are 85% and 6.9×10⁻⁴ Ω cm. Some Ag NP/ZnO transparent conducting oxide (TCO) films were applied to InGaN/GaN LEDs as transparent conductive layers. The InGaN/GaN LEDs with optimal Ag NP/ZnO TCO films showed electric and optical performance levels similar to those of devices fabricated with indium tin oxide.     

Structural properties of FeTe2 thin films synthesized by tellurization of amorphous iron oxide thin films

This paper deals with the structural properties of FeTe₂ thin films obtained using a simple and non-toxic experimental procedure. First, iron oxide thin films have been prepared by the spray pyrolysis technique from an aqueous solution containing FeCl₃6H₂O (0.03 M) as a precursor onto glass substrates heated at 623 K. Second, these films were subjected to a heat treatment under tellurium atmosphere at various temperatures (723–803 K) for 24 h. XRD analysis revealed that FeTe₂-ortorombic phase films were obtained at a heat treatment of the order of 773 K. This film has a good crystalline state with a preferential orientation of the crystallites along (111) direction. Moreover, AFM as well as SEM morphological observations show a relatively perturbed surface state.To date, this simple and low cost route process to obtained FeTe₂ thin films has not yet been used.     

Nanocrystalline Bi2S3 thin films grown by thio-glycolic acid mediated successive ionic layer adsorption and reaction (SILAR) technique

Bismuth sulfide (Bi₂S₃) nanocrystalline thin films were deposited on glass substrate by a simple and low-cost thioglycolic-assisted successive ionic layer adsorption and reaction method, using bismuth acetate and thioacetamide as cationic and anionic precursors respectively. Influence of cationic concentration on the structural, optical and electrical properties of Bi₂S₃ thin films were investigated. X-ray diffraction pattern revealed that the prepared Bi₂S₃ thin films are polycrystalline with orthorhombic structure. The surface morphology of Bi₂S₃ thin films examined by atomic force microscopy showed cluster like morphology, and having small hillocks of fairly uniform distribution. Optical studies showed a direct band-to-band transition, and the estimated optical band gap decreases from 1.81 eV to 1.25 eV with the increase in cationic concentration from 0.01 M to 0.03 M. Electrical resistivity measurements by four probe technique revealed negative temperature coefficient of resistance, which confirms the semiconducting nature of Bi₂S₃ thin films. The activation energy of Bi₂S₃ thin films was found to decrease from 0.059 eV to 0.022 eV with the increase in cationic concentration from 0.01 M to 0.03 M, which is attributed to improved grain size and reduction in the defect levels.     

Fabrication of Microstructured thermoelectric Bi2Te3 thin films by seed layer assisted electrodeposition

In this work, bismuth telluride (Bi₂Te₃) thin films have been fabricated on Bi₂Te₃/ITO substrates by constant potential electrochemical deposition at room temperature. Bi₂Te₃ seed layers with different thicknesses (2 nm, 4 nm and 6 nm) were deposited onto ITO substrates using molecular beam epitaxy (MBE) method. The SEM images show that the morphology of Bi₂Te₃ thin films can be controlled not only by the deposition potential, but also the thickness of seed layer. Moreover, the morphologies of Bi₂Te₃ thin films with different thickness of seed layers tend to be similar and contain two-layer structure along the vertical direction after prolonged deposition time. Due to the two layers structure, Bi₂Te₃ thin films have shown different electrical conductivity performances. At room temperature, Bi₂Te₃ thin films with 4 nm-thick seed layer possess the maximum electrical conductivity value of 617.9 s cm^-1.     

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.     

Electric conduction of PbBr-based layered perovskite organic–inorganic superlattice having carbazole chromophore-linked ammonium molecule as an organic layer

We have successfully prepared thin films of PbBr-based layered perovskite having hole-transporting carbazole chromophore-linked ammonium molecules as an organic layer by a simple spin-coating from the N,N-dimethylformamide solution in which the stoichiometric amount of lead bromide and carbazole-linked ammonium bromides was dissolved. Their X-ray diffraction profiles exhibited that their layer structure formed (0 0 n)-orientation, where c-axis is perpendicular to the substrate plane. Their layer structure depended on the alkyl chain length of ammonium molecules. When methylene length of C₅H₁₀ was employed in the carbazole-linked ammonium molecules, highest orderliness of the layer structure was attained; higher-order X-ray diffraction peaks were observed in the layered perovskite films. In the layered pervskite film, in-plane conduction, namely conduction in the direction of the stacking of carbazole chromophore, was measured. For comparison, conductivity of poly(N-vinylcarbazole) (PVCBz) thin film was also measured. The conductivity of the layered perovskite thin film (1.8 × 10^?10 Scm^?1 at 303 K) was about three order of magnitude larger than that of the PVCBz thin film (5.3 × 10^?14 Scm^?1 at 303 K). Despite the much higher conductivity of the layered peroskite thin film, the activation energy of the conductivity of the layered perovskite thin film (1.44 eV) was about 2.4 times larger than that of the PVCBz thin film (0.61 eV). This phenomenon is probably due to difference in film morphology through considering the results of AFM observation.     

Composition,structure and electrical properties of DC reactive magnetron sputtered Al2O3 thin films

Thin films of alumina (Al₂O₃) were deposited over Si 〈1 0 0〉 substrates at room temperature at an oxygen gas pressure of 0.03 Pa and sputtering power of 60 W using DC reactive magnetron sputtering. The composition of the as-deposited film was analyzed by X-ray photoelectron spectroscopy and the O/Al atomic ratio was found to be 1.72. The films were then annealed in vacuum to 350, 550 and 750 °C and X-ray diffraction results revealed that both as-deposited and post deposition annealed films were amorphous. The surface morphology and topography of the films was studied using scanning electron microscopy and atomic force microscopy, respectively. A progressive decrease in the root mean square (RMS) roughness of the films from 1.53 nm to 0.7 nm was observed with increase in the annealing temperature. Al–Al₂O₃–Al thin film capacitors were then fabricated on p-type Si 〈1 0 0〉 substrate to study the effect of temperature and frequency on the dielectric property of the films and the results are discussed.     

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.     

The effects of carrier gas and substrate temperature on ZnO films prepared by ultrasonic spray pyrolysis

ZnO films were deposited on glass substrates in the temperature range of 350–470 °C under an atmosphere of compressed air or nitrogen (N₂) by using ultrasonic spray pyrolysis technique. Structural, electrical and optical properties of the ZnO films were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), electrical two-probe and optical transmittance measurements. The ZnO films deposited in the range of 350–430 °C were polycrystalline with the wurtzite hexagonal structure having preferred orientation depending on the substrate temperature. The ZnO films deposited below 400 °C had a preferred (100) orientation while those deposited above 400 °C mostly had a preferred (002) orientation. The resistivity values of ZnO films depended on the types of carrier gas. The ZnO thin films deposited under N₂ atmosphere in the range of 370–410 °C showed dense surface morphologies and resistivity values of 0.6–1.1 Ω-cm, a few orders of magnitude lower than those deposited under compressed air. Hydrogen substition in ZnO possibly contributed to decreasing resistivity in ZnO thin films deposited under N₂ gas. The Hall measurements showed that the behavior of ZnO films deposited at 410 °C under the N₂ atmosphere was n-type with a carrier density of 8.9–9.2×10¹⁶ cm^-3 and mobility of ～70 cm²/Vs. ZnO thin films showed transmission values at 550 nm wavelength in a range of 70–80%. The values of band gaps extrapolated from the transmission results showed bandgap shrinkage in an order of milli electron volts in ZnO films deposited under N₂ compared to those deposited under compressed air. The calculation showed that the bandgap reduction was possibly a result of carrier–carrier interactions.     

Influence of magnesium doping on the structural and optical properties of tin (II) oxide thin films deposited by electron beam evaporation

Single-phase polycrystalline magnesium-doped tin oxide (Mg_xSn_1?xO; x=0, 0.04, and 0.08) thin films were deposited by electron beam evaporation on the glass substrate. X-ray diffraction analysis showed that the peaks intensity of the polycrystalline α-SnO thin films increased along with the increasing Mg content. The crystallite size calculated from X-ray diffraction data decreased by increasing the Mg doping concentration, which was also confirmed by atomic force microscopy. The stoichiometry and thickness of the thin films were determined by Rutherford backscattering spectroscopy. An increase in both the optical transmission (57–95%) and band gap (2.5–2.82 eV) of the Mg_xSn_1?xO thin films were observed which were investigated by UV–vis spectroscopy. Photoluminescence of Mg_xSn_1?xO thin films revealed that there were two extra peaks at 482 nm and 550 nm due to the crystal defects introduced by the Mg doping and these peaks become weaker and shifted to longer wavelength by increasing the Mg doping concentration.     

AC conductivity,dielectric relaxation and modulus behavior of Sb2S2O new kermesite alloy for optoelectronic applications

In this work, we present some physical properties of Sb₂S₂O thin films obtained through heat treatment of Sb₂S₃ thin films under an atmospheric pressure at 350 °C. The electrical conductivity, dielectric properties and relaxation model of these thin films were studied using impedance spectroscopy technique in the frequency range from 5 Hz to 13 MHz at various temperatures from 350 °C to 425 °C. Besides, the frequency and temperature dependence of the complex impedance, AC conductivity and complex electric modulus has been investigated.     

Effect of four different zinc salts and annealing treatment on growth,structural, mechanical and optical properties of nanocrystalline ZnS thin films by chemical bath deposition

ZnS thin films were deposited from four different zinc salts on glass substrates by chemical bath deposition method. Different anions of zinc salts affect the deposition mechanism and growth rate, which influence the properties of the films significantly. The ZnS thin film deposited from ZnSO₄ is smoother, thicker, more homogeneous and compact, nearly stoichiometric, comparing with the films deposited from Zn(CH₃COO)₂ and Zn(NO₃)₂, and ZnCl₂. The scratch test of bonding force between ZnS film and substrate shows that the ZnS film deposited from ZnSO₄ has the most excellent adhesion with the substrate. The presence of SO₄²⁻ promotes heterogeneous ZnS thin film growth via ions by ions deposition, and the films deposited from Zn(CH₃COO)₂ and Zn(NO₃)₂ are formed via clusters by clusters deposition. XRD and HRTEM results show that cubic ZnS films are obtained after single deposition, and the grain size of ZnS thin film deposited from ZnSO₄ for 2.5 h is 10 nm. The average transmission of all films is greater than 85% in the wavelength ranging from 600 to 1100 nm, and the transmission of films deposited from ZnSO₄ or Zn(NO₃)₂ for 1.5, 2 and 2.5 h is greater than 85% in the wavelength varying from 340 to 600 nm, which can enhance the blue response. The band gaps of all ZnS thin films are in the range of 3.88–3.99 eV. After annealing treatment, the mechanical and optical properties of the ZnS thin film deposited from ZnSO₄ are improved significantly.     

CdS amorphous thin films photochemical synthesis and optical characterization

Thin amorphous nanostructured CdS films were photochemically obtained via direct UV radiation (λ=254 nm) of complex Cd[(CH₃)₂CHCH₂CH₂OCS₂]₂ on Si(1 0 0) and ITO-covered glass substrate by spin coating. Thin cadmium xanthate complex films’ UV photolysis results in loss of all ligands from the coordination sphere. X-ray photoelectron spectra for as-deposited CdS thin films show the most representative signals of Cd 3d_5/2 located at 405 eV, Cd 3d_3/2 located at 412 eV and a small signal S 2p located at 162 eV. The surface morphology of the films was examined via atomic force microscopy. This can be described as a fibrous-type surface without structural order, which is characteristic of an amorphous deposit. The optical band gap value was 2.85 and 3.15±0.1 eV.     

Enhancement in electrical performance of indium gallium zinc oxide-based thin film transistors by low temperature thermal annealing

We have studied the characteristics of transparent bottom-gate thin film transistors (TFTs) using In–Ga–Zn–O (IGZO) as an active channel material. IGZO films were deposited on SiO₂/Si substrates by DC sputtering techniques. Thereafter, the bottom-gate TFT devices were fabricated by depositing Ti/Au metal pads on IGZO films, where the channel length and width were defined to be 200 and 1000 μm, respectively. Post-metallization thermal annealing of the devices was carried out at 260, 280 and 300 °C in nitrogen ambient for 1 h. The devices annealed at 280 °C have shown better characteristics with enhanced field-effect mobility and high on–off current ratio. The compositional variation of IGZO films was also observed with different annealing temperatures.     

YBCO/YSZ coated conductors on flexible Ni alloy substrates

A coating system for the deposition of in-plane oriented yttria-stabilized zirconia (YSZ) template films on 1 cm wide flexible metal substrates is presented. In static mode, the system is capable of producing high quality template films on 20 cm substrate lengths. In a continuous coating mode, the system is capable of producing good quality template films on 1.1 m substrate lengths. Superconducting YBa₂Cu₃O_7−δ (YBCO) films subsequently deposited onto these template films have demonstrated critical currents (I_c) of 200 A (1.5 cm length), 70 A (12 cm length) and 4 A (1 m length).     

Effects of ammonia concentration on property of Cd1−xZnxS films by chemical bath deposition

Cd_1−xZn_xS thin films were grown on soda–lime glass substrates by chemical-bath deposition (CBD) at 80 °C with stirring. All the samples were annealed at 200 °C for 60 min in the air. The crystal structure, surface morphology, thickness and optical properties of the films were studied with transmission electron microscopy (TEM), X-ray diffraction (XRD), scanning electron microscopy (SEM), step height measurement instrument and spectrophotometer respectively. The results revealed that Cd_1−xZn_xS thin films had cubic crystal structure and the intensity of the diffraction peak increased gradually as ammonia concentration rose and the grain size varied from 5.1 to 8.3 nm. All of Cd_1−xZn_xS thin films had a granular surface with some smaller pores and the average granule sizes increased from 92 to 163 nm with an increase in ammonia concentration. The Cd_1−xZn_xS thin films had the highest transmittance with ammonia concentration of 0.5 M L⁻¹, whose thickness was 50 nm and band gap was 2.62 eV.     

Effects of RTA temperatures on conductivity and micro-structures of boron-doped silicon nanocrystals in Si-rich oxide thin films

In this work, the B-doped Si rich oxide (SRO) thin films were deposited and then annealed using rapid thermal annealing (RTA) to form SiO₂-matrix silicon nanocrystals (Si NCs). The effects of the RTA temperatures on the structural properties, conduction mechanisms and electrical properties of B-doped SRO thin films (BSF) were investigated systematically using Hall measurements, Fourier transform infrared spectroscopy and Raman spectroscopy. Results showed that the crystalline fraction of annealed BSF increased from 41.3% to 62.8%, the conductivity was increased from 4.48×10⁻³ S/cm to 0.16 s/cm, the carrier concentration was increased from 8.74×10¹⁷ cm⁻³ to 4.9×10¹⁸ cm⁻³ and the carrier mobility was increased from 0.032 cm² V⁻¹ s⁻¹ to 0.2 cm² V⁻¹ s⁻¹ when the RTA temperatures increased from 1050 °C to 1150 °C. In addition, the fluctuation induced tunneling (FIT) theory was applicable to the conduction mechanisms of SiO₂-matrix boron-doped Si-NC thin films.     

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.     

Substrate temperature effect on structural,optical and electrical properties of vacuum evaporated SnO2 thin films

Tin oxide (SnO₂) thin films were deposited on glass substrates by thermal evaporation at different substrate temperatures. Increasing substrate temperature (T_s) from 250 to 450 °C reduced resistivity of SnO₂ thin films from 18×10⁻⁴ to 4×10⁻⁴▒ Ω ▒cm. Further increase of temperature up to 550 °C had no effect on the resistivity. For films prepared at 450 °C, high transparency (91.5%) over the visible wavelength region of spectrum was obtained. Refractive index and porosity of the layers were also calculated. A direct band gap at different substrate temperatures is in the range of 3.55−3.77 eV. X-ray diffraction (XRD) results suggested that all films were amorphous in structure at lower substrate temperatures, while crystalline SnO₂ films were obtained at higher temperatures. Scanning electron microscopy images showed that the grain size and crystallinity of films depend on the substrate temperature. SnO₂ films prepared at 550 °C have a very smooth surface with an RMS roughness of 0.38 nm.     

Amorphous ternary rare-earth gate oxides for future integration in MOSFETs

In this contribution we present results on the structural and electrical properties of amorphous REScO₃ (RE = La, Gd, Tb, Sm) and LaLuO₃ thin films. The study reveals that these oxides are potential candidates for so-called higher-k dielectrics for forthcoming MOSFET generations. High dielectric constants up to 32, low leakage currents and low interface trap densities are determined for amorphous thin films prepared by pulsed-laser deposition, molecular beam deposition and e-gun evaporation. Moreover, we show that LaLuO₃ gate stacks annealed up to 1050 °C maintain low leakage current densities without substantial EOT increase. Finally, promising results for n-MOSFETs with GdScO₃ as gate dielectric processed on strained silicon-on-insulator substrates are also shown.