Dispersive optical constants and electrical properties of nanocrystalline CuInS2 thin films prepared by chemical spray pyrolysis

Nanocrystalline CuInS₂ thin films were deposited on borosilicate glass substrates via chemical spray pyrolysis method. The structural, morphological, optical, and electrical properties were studied as a function of increasing annealing temperature from 250 to 350 ̊C. XRD analysis showed mixed phases at lower temperatures with the preferred orientation shifting towards the (112) chalcopyrite CuInS₂ plane at higher substrate temperature. The crystallite size increased slightly between 13 and 18 nm with increase in annealing temperature. The optical band gap was determined on basis of Tauc extrapolation method and the Wemple–Di-Domenico single oscillator model. Possible structural and quantum confinement effect may have resulted in relatively larger band gaps of 1.67–2.04 eV, relative to the bulk value of 1.5 eV. The presence of Cu_xS in the as-deposited and wurtzite peaks after annealing at 350 ^̊C play a role in influencing the optical and electrical properties of CuInS₂ thin films.     

A Functional Material Based Heterojunction Diode

In this study, the phosphotungstic acid /p-Si diode was fabricated by a drop coating method. The fabricated diode had excellent rectifying properties. The electrical properties of the diode were investigated in the temperature range of 50-400 K. The optical band gap of the phosphotungstic acid film was determined and found to be 3.66 eV. The electrical and photoresponse properties of an Al/p-Si-phosphotungstic acid/Al photodiode were studied. The electronic parameters such as ideality factor (n), barrier height (Φ _B ) and series resistance (R _s ) were found to be strongly temperature dependent.     

Microstructural and optical properties of SnO2–ZnSnO3 ceramics

This work deals with some physical investigation on SnO₂–ZnSnO₃ ceramics grown on glass substrates at different temperatures (450 °C and 500 °C). Structural and optical properties were investigated using X-Ray diffraction (XRD), Raman, infrared (IR) absorption (FTIR), UV–visible spectroscopy and Photoluminescence (PL) techniques. XRD results revealed the existence of a mixture of SnO₂/ZnSnO₃ phases at different annealing temperatures. Structural analysis showed that both phases are polycrystalline. On the other hand, the optical constants (refractive index, extinction coefficient and the dielectric constants) have been obtained by the transmittance and the reflectance data. The optical band gap energy changed from 3.85 eV to 3.68 eV as substrate temperature increased from 450 °C to 500 °C. Raman, FTIR modes and PL reinforced this finding regarding the existence of biphasic (SnO₂ and ZnSnO₃) which is detected also by X-Ray diffraction analysis. Finally, the Lattice Compatibility Theory was evoked for explaining the unexpected incorporation of zinc ions in a rhombohedral structure within SnO₃ trigonal lattice, rather than the occupation of SnO₂ available free loci. All the results have been discussed in terms of annealing temperature.     

Influence of Heat Treatment on the Optical Properties of Thermal Evaporated SnO<Subscript>2</Subscript> Thin Films

In this investigation, the optical properties of the thermally evaporated SnO₂ films and their dependence on the heat treatment were studied. The transmittance, T (λ), spectra were measured over the spectral range of 0.2 to 0.8 μm for SnO₂ films that were annealed at different temperatures (300, 350, 400, 450, 500, 550 and 600 K) in vacuum for 1h. All films showed high transparency in the visible range and increased with increasing the wavelength. These films have become more transparent after annealing at different temperatures. The optical constants of annealed SnO₂ films were obtained by modeling the measured transmission spectra. The best fit modeling of transmission spectra was obtained by applying Drude and OJL models combined with the effective medium approximation Bruggeman model. Increasing the annealing temperatures decreased both the refractive index and the extinction coefficient of the films. While the optical band gap energy increased from 3.05 to 4.11 eV by increasing the annealing temperature from 300 to 600 K, respectively. Analyzing the refractive index dispersion by using the Wemple-DiDomenico model revealed that the oscillator resonance energy E_o decreased whereas the oscillator dispersion energy E_d increased with increasing the annealing temperature.     

Schottky barrier effect of ZnO modified methyl glycol thin films for detection of hydrogen sulfide gas

Highly nanocrystalline ZnO modified methyl glycol thin films have been deposited on a p-type silicon substrate via the sol–gel spin coating manner. The morphology of the as-deposited film was scrutinized using scanning electron microscopy. I–V characteristics of the as-prepared ZnO film under vacuum and in open air were monitored. The results showed that the ZnO films have a barrier height of 0.38 eV under vacuum and 0.62 eV in open air. The Schottky barrier height between ZnO grains was determined for different reducing gases. The ZnO film showed high sensitivity to H₂S gas compared with other reducing gases due to the reduction of barrier height between ZnO grains. The as-prepared ZnO film was annealed at four different temperatures. X-ray diffraction manifested that the wurtzite hexagonal structure of ZnO deviated from ideality at annealing temperature greater than 650 °C. The barrier height of ZnO film decreased due to the increase of annealing temperature up to 650 °C and then decreased. The results also confirmed that the change of barrier height strongly affected the sensitivity of ZnO film.     

TiO2 based nanopowder coatings over stainless steel plates for UV-C photocatalytic degradation of methylene blue

Immobilizing the photocatalyst in a water treatment process design is essential; however, the immobilization method may affect the photoactivity of the photocatalyst. In this work, photocatalyst powders were successfully coated on 316 L stainless steel plates by a novel brush coating method. Three combinations of photocatalyst mixtures (pure TiO₂ anatase, anatase doped with WO₃, or TiO₂ rutile) were and annealed at different temperatures between 460-540°C. The ~ 10 μm thick coatings demonstrated full plate coverage and strong adhesion and adequate durability. Surface roughness increased with annealing temperature. The doping and annealing process enabled band gap reduction to the visible light spectrum for all coatings, with the smallest band gap being 2.48 eV (1 eV = 1.6 × 10⁻¹⁹ J). Subsequent methylene blue degradation tests under UV-C showed that the coatings annealed in 460°C exhibited the best performance and with the highest degradation rate constant of 5.59 hours⁻¹.     

Enhanced electrical properties of In-Ga-Sn-O thin films at low-temperature annealing

Electrical and optical properties of In-Ga-Sn-O (IGTO) thin films deposited by radio-frequency magnetron sputtering were investigated according to annealing temperatures. While IGTO films remained an amorphous phase even after a heat treatment at temperature up to 500 °C, Hall measurements showed that annealing temperature had a significant impact on electrical properties of IGTO thin films. After investigating a wide range of annealing temperatures for samples from as-deposited state to 500 °C, IGTO film annealed at 200 °C exhibited the best electrical performance with a conductivity of 229.31 Ω^?1cm^?1, a Hall mobility of 36.89 cm²V^?1s^?1, and a carrier concentration of 3.85 × 10¹⁹ cm^?3. Changes in proportions of oxygen-related defects and percentages of Sn²⁺ and Sn⁴⁺ ions within IGTO films according to annealing temperatures were analyzed with X-ray photoelectron spectroscopy to determine the cause of the superb performance of IGTO at a low temperature. In IGTO films annealed at 200 °C, Sn⁴⁺ ions acting as donor defects accounted for a high percentage, whereas hydroxyl groups working as electron traps showed a significantly reduced percentage compared to the as-deposited film. Optical band gaps of IGTO films obtained from UV–visible spectrum were 3.38–3.47 eV. The largest band gap value of 3.47 eV for the IGTO film annealed at 200 °C could be attributed to an increase in Fermi-level due to an increase of carrier concentration in the conduction band. These spectroscopic results well matched with electrical properties of IGTO films according to annealing temperatures. Excellent electrical properties of IGTO thin films annealed at 200 °C could be largely due to Sn donors besides oxygen vacancies, resulting in a significant increase in free carriers despite a low annealing. temperature.     

Oxygen vacancy luminescence and band gap narrowing driven by Ce ion doping with variable valence in SnO2 nanocrystals

Although considerable research works have witnessed the important modulations of oxygen vacancies on the optical, electrical, and magnetic properties of SnO₂ nanostructures, it is not easy to control oxygen vacancy defects in such systems.The difficulty stems from that oxygen vacancy is a kind of atomic defect, and its distribution is sensitive to process conditions and external factors, which makes direct characterization and purposeful control difficult. The purpose of this work on Ce-doped SnO₂ nanocrystals is to investigate the tolerance of the host lattice to Ce ions, the population and evolution of Ce³⁺/Ce⁴⁺ ions, and the possibility to adjust oxygen vacancies by Ce³⁺ ions, and then focus on the influence of oxygen vacancy defects on the band gap and luminescence performance. As Ce doping concentration increases from 0 to 12 at.%, the doped system changes from Ce³⁺ dominated at low doping amount (≤3 at.%) to Ce³⁺/Ce⁴⁺ coexistence at medium doping concentration (3 at.% ∼ 9 at.%), to occurrence of CeO₂ impurity phase at over doping (∼12 at.%). The optimum doping occurs at 6 at.%, which corresponds to the saturated critical point of Ce³⁺ content and the maximum oxygen vacancy concentration. Importantly, the oxygen vacancies in the current Ce-doped SnO₂ nanocrystals is directly regulated by the Ce³⁺ ion concentration on the Sn sites, which plays an important role in the band gap tuning and visible light emission. With Ce concentration increasing from 0 to 12 at.%, the band gap monotonicity decreases from 3.36 eV to 3.12 eV, while the intensity of the oxygen vacancy luminescence band first increases and then decreases, with the turning point at 6 at.%. Both band gap narrowing effect and enhanced emission indicate that Ce-doped SnO₂ should be a promising method to design and manufacture visible light responsive SnO₂ based optoelectronic materials by manipulating oxygen vacancy defects.     

Al3+ doping induced changes of structural,morphology, photoluminescence,optical and electrical properties of SnO2 thin films as alternative TCO for optoelectronic applications

Highly transparent and conductive pure (SnO₂) and aluminum doped tin oxide (Al:SnO₂) thin films were deposited on glass substrates by the sol-gel spin-coating method. The structural, morphological, optical and electrical properties of the prepared thin films at different doping rates have been studied. X-ray diffraction results revealed that all the films were polycrystalline in nature with a tetragonal rutile structure. SEM images of the analyzed films showed a homogeneous surface morphology, composed of nanocrystalline grains. The EDS results confirmed the presence of Sn and O elements in pure SnO₂ and Sn, O, Al in doped SnO₂ thin films. The optical results revealed a high transmittance greater than 85% in the visible and near infrared and a band gap varying between 3.82 and 3.89 eV. PL spectra at room temperature showed that the most dominant defects correspond to oxygen vacancies. A low resistivity of order varying between 10^?3 and 10^?4 Ω cm and a high figure of merits ranging between 10^?3 and 10^?2 Ω^?1 in the visible range were obtained. The best performances were obtained for samples containing 2 at. % Al, which could be used as an alternative TCO layer for future optoelectronic devices.     

Solid-Phase Synthesis of Non-metal (S,N)-Doped Tin Oxide Nanopowders at Room Temperature and its Photodegradation Properties for Wastewater of Biomass Treatment

Tin oxide and sulfur, nitrogen-doped tin oxide nano-powder catalysts were prepared by a solid phase reaction at room temperature, using the sodium p-toluene sulfonate (STS) surfactant as template. Theoretical calculation of the dehydration reaction energy of tin hydroxide was performed with the framework of DFT and their structures were characterized. And the UV-light degradation performance and mechanism used for the biomass wastewater were discussed, as well as, its COD and NH₃-N value. The results show that the large gap of the reaction energy between intramolecular dehydration (Er?=?2.81 eV) and intermolecular dehydration (Er?=?5.77 eV) for tin hydroxide causes the presence of amorphous SnO₂ and metastable tin hydroxide at 450 °C. The entry of S and N into the (110) crystal plane of SnO₂ reduces its energy band gap width, exhibiting the photocatalytic degradation rate (98.9%) of S?+?N-SnO₂-_STS sample for the rice straw powder treatment wastewater (RSPTW) irradiated by UV-light for 8 h. The excellent degradation capacity of RSPTW mainly comes from the hydroxyl radicals (·OH) and superoxygen radicals (·O₂^?) produced by the rich hydroxyl on the surface of S?+?N-SnO₂-_STS due to the regulatory effect of STS and lower calcined temperature. The sewage discharge of photodegraded RSPTW complies with Chinese National Level II Standards.

     

Fabrication of spray derived nanostructured n-ZnO/p-Si heterojunction diode and investigation of its response to dark and light

Fluorine doped ZnO thin films were grown by chemical spray pyrolysis technique of zinc acetate and ammonium fluoride, and the effect of fluorine content on structural, optical and electrical properties were evaluated. The structural, morphological, optical properties of ZnO films were investigated by XRD (X-ray diffraction), AFM (Atomic force microscopy), SEM (Scanning electron microscop) and UV–Vis spectroscopy, respectively. According to results, it was observed that all films had polycrystalline texture with hexagonal wurtzite crystal structure and film surface were made up of nano-scale grains, varied by fluorine content. Optical properties showed that optical band gap energy of ZnO changed from 3.28 to 3.24 eV with F content. Shrinkage effect was assessed as the cause in the variation of optical band gap values. Finally, current-voltage (I-V) analysis was performed in Au/ZnO:F/p-Si device in dark and light conditions and certain diode parameters such as ideality factor, barrier height and series resistance were calculated and discussed in detail.     

Heat treatment effects on the structural and optical properties of thin Bi2(Se1-xTex)3 films

Thin layers of Bi₂-chalcogenides, in the form of Bi₂(Se_1-xTe_x)₃ films, were evaporated on glass substrates by means of the vacuum thermal evaporation. Microstructure of the as prepared layers was investigated by x-ray diffraction (XRD) analysis. Identifications of the surface morphology and roughness were determined via scanning electron microscope (SEM). Optical transmissivity spectra proved that the as prepared films have low transparency with growing trend upon increasing the wavelength beyond the infra-red region. Low transmittance was observed for the as prepared films. Heat treatment, in the form of temperature annealing, was carried out aiming at boosting the structural features and the materials transmissivity. Structural properties and surface features of the annealed films were probed also via XRD and SEM analyses. It was found that the crystal size increases while the micro-strain and the dislocation density decrease obviously due to annealing. It was also observed that the annealing process significantly enhances the materials transmission especially in the range of higher wavelengths. Optical band gap was studied after annealing at various temperatures. Notable change in the band gap value was observed as a result of annealing. The band gap of the undoped (Bi₂Se₃) materials showed significant rise from 0.14 to 1.79 eV due to annealing. Similarly, the Te-doped samples exhibited notable increase in their band gap values after annealing. For example, the optical band gap of the sample doped at x = 0.20 increased from 0.03 to 0.41 eV by annealing. On the other hand, transmittance was also enhanced by annealing. For samples treated at 250 °C for 3 h, their optical transmissivity is enhanced to over 99% at the visible near-IR range. Such significant enhancement can be ascribed to structural enhancements. With such enhancement in the optical transmissivity, optoelectronic applications including transparent electrode can be met.     

Structural/Optical Properties and CO Oxidation Activities of SnO2 Nanostructures

Tetragonal SnO₂ nanostructures with different sizes, band gaps, and defects were synthesized by varying the amounts of ammonia and polyethylene glycol (PEG) used during production and their structural and optical properties were characterized by scanning electron microscopy (SEM), X‐ray diffraction (XRD) crystallography, BET surface area analysis, thermogravimetric analysis, Raman spectroscopy, UV–visible absorption spectroscopy, photoluminescence imaging, and X‐ray photoelectron spectroscopy. In addition, the CO oxidation activity was examined by temperature‐programmed reduction and temperature‐programmed CO oxidation measurements. SEM and XRD analysis revealed that the particle size decreased with increasing PEG, but increased with increasing ammonia. Additionally, the band gaps decreased with increasing ammonia, but not with increasing PEG. Tetragonal SnO formed when larger amounts of ammonia were used, and this was converted to SnO₂ upon annealing at temperatures up to 700°C. The SnO₂ showed a unique strong green emission at 560 nm, which was attributed to a new oxygen deficiency. In addition, a sharp (328 nm) and two broad (390 and 460 nm) photoluminescence peaks corresponding to gap emission and the oxygen vacancies, respectively, were observed. The difference in CO oxidation activity with SnO₂ was attributed to varying sizes and defects formed in response to preparation under different reaction conditions.     

A Tunneling Current Model with a Realistic Barrier for Ultra-Thin High-k Dielectric ZrO2 Material Based MOS Devices

In this paper, a theoretical model to estimate the tunneling current density of ultra-thin MOS devices is presented. First an ideal barrier has been assumed for the modeling. Then development in the results is brought in by taking into account the barrier height lowering due to the image force effect (practical barrier). The SiO₂ material with selected high-k dielectric material ZrO₂ based MOS structure is used to verify the tunneling current density model against the 2-D device simulator, ATLAS of Silvaco TCAD for a wide variation of oxide thickness and biasing conditions having doping concentration of 5 × 10¹⁷ cm^− 3. Tunnel resistivity is also evaluated utilizing this tunneling current density model. Excellent agreement between the two are observed.

     

Potential Barrier of (Zn,Nb)SnO2‐Films Induced by Microwave Thermal Diffusion of Cr3+ for Low‐Voltage Varistor

The effect of Cr³⁺ on the electrical properties of SnO₂‐based films deposited by electrophoresis on Si/Pt substrate was considered. The films were sintered in a microwave oven at 1000°C/40 min and then the surface was modified with deposition of Cr³⁺ ions by electrophoresis. The diffusion of Cr³⁺ contributes to the modification of the potential barrier formed on the grain boundary improving the electrical properties due to electron acceptor species adsorption on the grain boundary. The influence on the properties of grain boundary was verified by I versus V characterization in as a function of temperature. The films showed nonlinear coefficient over 9, potential barrier height over 0.5 eV and resistivity greater than 10⁷ Ω·cm. 4 samples were prepared at same conditions and presented similar electrical behavior, showing the efficiency of technique on reproducibility to varistor properties control. Thereby the nonlinear coefficient increases while decreasing the conductivity of the system is noticed.     

AgSbTe2 semi-nanocrystalline thin films as a multifunctional platform for optoelectronic and diode applications

The synthesis of the nanosized multifunctional thin film provides new solutions for many technological issues and consider a great step for miniaturized technology. Toward these goals, AgSbTe₂ semi-nanocrystalline thin films of different thicknesses were synthesized by the thermal evaporation technique. The structural features were investigated by X-ray diffraction, and selected area electron diffraction (SAED) yielding a semi-nanocrystalline thin film of grain size ranging from 9.98 to 21.38 nm. The energy-dispersive X-ray spectroscopy (EDAX) verified the high purity and stoichiometry of the deposited films. For optoelectronic application, many optical parameters, including band gap (E_g), Urbach energy (E_u), Refractive index (n), dispersion energy (E_d), electronic polarizability (α_e), and interband transition strength (J_CV) were extensively discussed. The optical band gap reduced from 1.41 to 1.04 eV upon increasing the thickness from 150 to 550 nm. The temperature dependence of the electrical resistivity (ρ) of nanosized thin film was measured and the activation energy was estimated and it was found that the resistivity increased up to 450 K asserting the semiconductor behavior of the films. As for diode application, The Ag/2D-MoS₂/p-AgSbTe₂ (550 nm)/n-Si/Al heterostructure diode was constructed by thermal evaporation and all the diode parameters alongside conduction mechanism were studied in detail. AgSbTe₂-based diode showed a low rectification ratio; however, the ideality factor (n) and zero bias barrier height (Φ_b) had optimal values of about 1.40 and 0.75 at room temperature, respectively.     

Structural,photoelectrical and photoluminescence properties of Ta-doped SnO2 monocrystal films grown on MgF2 (110) substrates

Epitaxial Ta-doped SnO₂ films with Ta concentrations from 0 to 8?at.% have been deposited on MgF₂ (110) substrates by the metal-organic chemical vapor deposition (MOCVD) method. The effects of Ta doping on the structural, photoelectrical and photoluminescence (PL) properties of the obtained films were studied in detail. The results showed that the single crystal rutile SnO₂ films were obtained and the heteroepitaxial relationship was SnO₂ (110) || MgF₂ (110) with SnO₂ [001] || MgF₂ [001]. The highest Hall mobility of 74.2?cm²?V^?1?s^?1 was achieved for the 5?at.% Ta-doped SnO₂ film and the minimum resistivity as low as 2.5?×?10^?4?Ω?cm was obtained at 6?at.% of Ta-doping. In the visible region, all the obtained films had average transmittances exceeding 87%. As the Ta concentration increased from 0 to 8?at.%, the optical band gap of the films rose from 3.89 to 4.32?eV. The room temperature PL spectra of Ta-doped SnO₂ films showed intense green emission, weak violet and yellow emissions. The corresponding PL mechanisms were discussed.     

Effects of post-deposition annealing ambient on band alignment of RF magnetron-sputtered Y2O3 film on gallium nitride

The effects of different post-deposition annealing ambients (oxygen, argon, forming gas (95% N₂ + 5% H₂), and nitrogen) on radio frequency magnetron-sputtered yttrium oxide (Y₂O₃) films on n-type gallium nitride (GaN) substrate were studied in this work. X-ray photoelectron spectroscopy was utilized to extract the bandgap of Y₂O₃ and interfacial layer as well as establishing the energy band alignment of Y₂O₃/interfacial layer/GaN structure. Three different structures of energy band alignment were obtained, and the change of band alignment influenced leakage current density-electrical breakdown field characteristics of the samples subjected to different post-deposition annealing ambients. Of these investigated samples, ability of the sample annealed in O₂ ambient to withstand the highest electric breakdown field (approximately 6.6 MV/cm) at 10⁻⁶ A/cm² was related to the largest conduction band offset of interfacial layer/GaN (3.77 eV) and barrier height (3.72 eV).     

Growth and properties of Cu3SbS4 thin films prepared by a two-stage process for solar cell applications

Cu₃SbS₄ is a promising material for thin film heterojunction solar cells owing to its suitable optical and electrical properties. In this paper, we report the preparation of Cu₃SbS₄ thin films by annealing the Sb₂S₃/CuS stacks, produced by chemical bath deposition, in a graphite box held at different temperatures. The influence of annealing temperature on the growth and properties of these films is investigated. These films are systematically analyzed by evaluating their structural, microstructural, optical and electrical properties using suitable characterization techniques. X-ray diffraction analysis showed that these films exhibit tetragonal crystal structure with the lattice parameters a=0.537 nm and b=1.087 nm. Their crystallite size increases with increasing annealing temperature of the stacks. Raman spectroscopy analysis of these films exhibited modes at 132, 247, 273, 317, 344, 358 and 635 cm⁻¹ due to Cu₃SbS₄ phase. X-ray photoelectron spectroscopy analysis revealed that the films prepared by annealing the stack at 350 °C exhibit a Cu-poor and Sb-rich composition with +1, +5 and −2 oxidation states of Cu, Sb and S, respectively. Morphological studies showed an improvement in the grain size of the films on increasing the annealing temperature. The direct optical band gap of these films was in the range of 0.82–0.85 eV. Hall measurements showed that the films are p-type in nature and their electrical resistivity, hole mobility and hole concentration are in the ranges of 0.14–1.20 Ω-cm, 0.05–2.11 cm² V⁻¹ s⁻¹ and 9.4×10²⁰–1.4×10¹⁹ cm⁻³, respectively. These structural, morphological, optical and electrical properties suggest that Cu₃SbS₄ could be used as an absorber layer for bottom cell in multi-junction solar cells.     

Structural, Electrical and Optical Properties of p-Type Transparent Conducting SnO2:Zn Film

Highly transparent, p-type conducting SnO₂:Zn films were deposited on quartz substrates by radio frequency (RF) magnetron sputtering using a 12 wt% ZnO doped with 88 wt% SnO₂ ceramic target followed by annealing at various temperatures. The effect of annealing temperature on the structural, electrical and optical performances of SnO₂:Zn films has been studied. XRD results show that all the SnO₂:Zn films possess tetragonal rutile structure with the preferred orientation of (101). Hall effect results indicate that at 873 K for 3 h was the optimum annealing parameters for p-type SnO₂:Zn films with relatively high hole concentration and low resistivity of 3.334 × 10¹⁹ cm⁻³ and 3.588 Ω cm, respectively. The average transmission of the p-type SnO₂:Zn films were above 80% in the visible light range. In addition, p-type conductivity was also confirmed by the non-linear characteristics of a p-type SnO₂:Zn/n-type SnO₂:Sb structure.