Physical properties of electrically conductive Sb-doped SnO2 transparent electrodes by thermal annealing dependent structural changes for photovoltaic applications

We have investigated the optical and electrical characteristics of antimony (Sb)-doped tin oxide (SnO₂) films with modified structures by thermal annealing as a transparent conductive electrode. The structural properties were analyzed from the relative void % by spectroscopic ellipsometry as well as the scanning electron microscopy images and X-ray diffraction patterns. As the annealing temperature was raised, Sb-doped SnO₂ films exhibited a slightly enhanced crystallinity with the increase of the grain size from 17.1 nm at 500 °C to 34.3 nm at 700 °C. Furthermore, the refractive index and extinction coefficient gradually decreased due to the increase in the relative void % within the film during the annealing. The resistivity decreased to 8.2 × 10⁻³ Ω cm at 500 °C, but it increased rapidly at 700 °C. After thermal annealing, the optical transmittance was significantly increased. For photovoltaic applications, the photonic flux density and the figure of merit over the entire solar spectrum were obtained, indicating the highest values of 5.4 × 10¹⁴ cm⁻² s⁻¹ nm⁻¹ at 1.85 eV after annealing at 700 °C and 340.1 μA cm⁻² Ω⁻¹ at 500 °C, respectively.     

Effect of annealing on the electrical, optical and structural properties of cadmium stannate thin films prepared by spray pyrolysis technique

Polycrystalline thin films of cadmium stannate (Cd₂SnO₄) were deposited by spray pyrolysis method on the Corning substrates at substrate temperature of 525 °C. Further, the films were annealed at 600 °C in vacuum for 30 min. These films were characterized for their structural, electrical and optical properties. The experimental results showed that the post-deposition annealing in vacuum has a significant influence on the properties of the films. The average grain size of the film was increased from 27.3 to 35.0 nm on heat treatment. The average optical transmittance in the visible region (500-850 nm) is decreased from 81.4% to 73.4% after annealing in vacuum. The minimum resistivity achieved in the present study for the vacuum annealed films is the lowest among the reported values for the Cd₂SnO₄ thin films prepared by spray pyrolysis method.     

Nanocrystalline SnO2 and Au:SnO2 thin films prepared by direct current magnetron reactive sputtering

Nanocrystalline pure and gold doped SnO₂(Au:SnO₂) films were prepared on unheated glass substrates by dc magnetron reactive sputtering and, subsequently, the as deposited films were annealed in air. The films structure, surface morphology, photoluminescence, electrical and optical properties were investigated. After annealing the as deposited SnO₂ films, crystallinity increased and the surface roughness decreased. The intensity of PL peaks increases sharply with the annealing temperature. The optical transmittance of the films was around 89% after annealing the as deposited SnO₂ films at 450 °C. The as deposited Au:SnO₂ films show better crystallinity than the as deposited SnO₂ films, the average grain size was around 4.4 nm. The emission peaks of Au:SnO₂ films are slightly blue shifted as compare to undoped SnO₂ films. The Au:SnO₂ films show the lowest electrical resistivity of 0.001 Ωcm with optical transmittance of 76%, after annealing at 450 °C.     

Effects of post-deposition surface treatment on the optical, structural and hydrogen sensing properties of TiO2 thin films

TiO₂ thin films were prepared by DC reactive magnetron sputtering in a mixture of oxygen and argon on glass and oxidized silicon substrates. The effect of post-deposition annealing (300 °C, 500 °C and 700 °C for 8 h in air) on the structural and morphological properties of TiO₂ thin films is presented. In addition, the effect of Pt surface modification (1, 3 and 5 nm) on hydrogen sensing was studied. XRD patterns have shown that in the range of annealing temperatures from 300 °C to 500 °C crystallization starts and the thin film structure changes from amorphous to polycrystalline (anatase phase). In the case of samples on glass substrate, optical transmittance spectra were recorded. TiO₂ thin films were tested as sensors of hydrogen at concentrations 10,000-1000 ppm and operating temperatures within the 180-200 °C range. The samples with 1 nm and in particular with 3 nm of Pt on the surface responded to hydrogen fast and with high sensitivity.     

The effect of Au and Pt nanoclusters on the structural and hydrogen sensing properties of SnO2 thin films

Au and Pt nanoparticle modified SnO₂ thin films were prepared by the sol-gel method on glass substrates targeting sensing applications. Structural and morphological properties of these films were studied using X-ray Diffraction and Scanning Electron Microscopy. It was proved that the films crystallized in tetragonal rutile SnO₂ crystalline structure. Scanning Electron Microscopy observations showed that the metallic clusters' dimensions and geometry depend on the kind of the metal (Au or Pt) while SnO₂ films surface remains almost the same: nanostructured granular very smooth. Optical properties of the films were studied using UV-visible spectroscopy. The modified SnO₂ films were tested as hydrogen sensors. The response of SnO₂, SnO₂-Au and SnO₂-Pt thin films against hydrogen was investigated at different operating temperatures and for different gas concentrations. The addition of metal nanoparticles was found to decrease the detection limit and the operating temperature (from 180 °C to 85 °C), while increasing the sensing response signal.     

F-doped SnO2 thin films grown on flexible substrates at low temperatures by pulsed laser deposition

Fluorine-doped tin oxide (SnO₂:F) films were deposited on polyethersulfone plastic substrates by pulsed laser deposition. The electrical and optical properties of the SnO₂:F films were investigated as a function of deposition conditions such as substrate temperature and oxygen partial pressure during deposition. High quality SnO₂:F films were achieved under an optimum oxygen pressure range (7.4-8 Pa) at relatively low growth temperatures (25-150 °C). As-deposited films exhibited low electrical resistivities of 1-7 mΩ-cm, high optical transmittance of 80-90% in the visible range, and optical band-gap energies of 3.87-3.96 eV. Atomic force microscopy measurements revealed a reduced root mean square surface roughness of the SnO₂:F films compared to that of the bare substrates indicating planarization of the underlying substrate.     

Optical and electrical properties of heat-resistant Sb-doped Sn1 − xHfxO2 transparent conducting films

To examine variations in the transparent conducting properties after annealing at high temperatures, 300-nm thick Sb-doped Sn_1 − xHf_xO₂ (x = 0.00-0.10) films were deposited onto silica glass substrates by the RF sputtering method and annealed in air up to 1000 °C at 200 °C increments. After annealing, all the Sb-doped SnO₂ films were transparent and electrically conductive, but large cracks, which decreased the electrical conductivity, were generated in several films due to crystallization or the thermal expansion difference between the film and substrate. Only the film deposited at room temperature in an Ar and O₂ mixed atmosphere did not crack after annealing, and its electrical conductivity exceeded 100 S cm^− 1 even after annealing at 1000 °C in air. Hf-doping blue shifted the fundamental absorption edges in the UV region in the Sb-doped Sn_1 − xHf_xO₂ films. Additionally, the optical transmission at 310 nm, T₃₁₀, increased as the Hf concentration increased, whereas the electrical conductivity was inversely proportional to the Hf concentration. On the other hand, thinner films (150-nm thick) with x = 0.00 showed both a high electrical conductivity over 100 S cm^− 1 and a high transparency T₃₁₀ = 65% after high temperature annealing.     

Preparation and characterization of transparent semiconductor RuO2-SiO2 films synthesized by sol-gel route

RuO₂-SiO₂ thin films with different Si/Ru molar ratios were prepared by the sol-gel method, using the hydrate ruthenium (III) chloride (RuCl₃·3.5H₂O) and tetraethylorthosilicate as precursors. The crystal structure, resistivity, chemical bonding configuration, transmittance, carrier concentration, and mobility of the RuO₂-SiO₂ films were investigated before and after annealing in N₂ ambient at 400-700 °C. The resistivity of the RuO₂-SiO₂ films with different Si/Ru molar ratios decreased abruptly after annealing at 400-700 °C. On the other hand, RuO₂ phase precipitated in the RuO₂-SiO₂ films with different Si/Ru molar ratios after annealing. Fourier transform infrared spectroscopy spectra indicated that the water absorption occurs for as-deposited RuO₂-SiO₂ films with different Si/Ru molar ratios. The transmittance of all RuO₂-SiO₂ films presented transmittance maximums after annealing at 700 °C. The carrier concentration and mobility of RuO₂-SiO₂ films are related to the Si/Ru molar ratios and the annealing temperature. This study discusses the connection among the material properties of the RuO₂-SiO₂ films and how they are influenced by the Si/Ru molar ratios and the annealing temperatures of RuO₂-SiO₂ films.     

Characterization and optoelectronic properties of sol-gel-derived CuFeO2 thin films

In this study, CuFeO₂ thin films were deposited onto quartz substrates using a sol-gel and a two-step annealing process. The sol-gel-derived films were annealed at 500 °C for 1 h in air and then annealed at 600 to 800 °C for 2 h in N₂. X-ray diffraction patterns showed that the annealed sol-gel-derived films were CuO and CuFe₂O₄ phases in air annealing. When the films were annealed at 600 °C in N₂, an additional CuFeO₂ phase was detected. As the annealing temperature increased above 650 °C in N₂, a single CuFeO₂ phase was obtained. The binding energies of Cu-2p_3/2, Fe-2p_3/2, and O-1s were 932.5 ± 0.1 eV, 710.3 ± 0.2 eV and 530.0 ± 0.1 eV for CuFeO₂ thin films. The chemical composition of CuFeO₂ thin films was close to its stoichiometry, which was determined by X-ray photoelectron spectroscopy. Thermodynamic calculations can explain the formation of the CuFeO₂ phase in this study. The optical bandgap of the CuFeO₂ thin films was 3.05 eV, which is invariant with the annealing temperature in N₂. The p-type characteristics of CuFeO₂ thin films were confirmed by positive Hall coefficients and Seebeck coefficients. The electrical conductivities of CuFeO₂ thin films were 0.28 S cm^− 1 and 0.36 S cm^− 1 during annealing at 650 °C and 700 °C, respectively, in N₂. The corresponding carrier concentrations were 1.2 × 10¹⁸ cm^− 3 (650 °C) and 5.3 × 10¹⁸ cm^− 3 (700 °C). The activation energies for hole conduction were 140 meV (650 °C) and 110 meV (700 °C). These results demonstrate that sol-gel processing is a feasible preparation method for delafossite CuFeO₂ thin films.     

Effect of post-annealing treatment in oxygen on dielectric properties of K0.5Na0.5NbO3 thin films prepared by chemical solution deposition

K_0.5Na_0.5NbO₃ thin films were prepared on Pt/Ti/SiO₂/Si substrates by chemical solution deposition method with different annealing temperatures of 550 °C, 600 °C, 700 °C. The post-annealing treatment was introduced at 550 °C for 3 min in oxygen ambient. It is found that the films were composed of pure provskite phase, and the post-annealing treatment promoted the crystallization and improved the quality of the films, which resulted in the enhancement of the dielectric property of the films. The effect of the post-annealing on the dielectric properties of the films was also discussed.     

The effect of annealing on Al-doped ZnO films deposited by RF magnetron sputtering method for transparent electrodes

In this study, transparent conducting Al-doped zinc oxide (AZO) films with a thickness of 150 nm were prepared on Corning glass substrates by the RF magnetron sputtering with using a ZnO:Al (Al₂O₃: 2 wt.%) target at room temperature. This study investigated the effects of the post-annealing temperature and the annealing ambient on the structural, electrical and optical properties of the AZO films. The films were annealed at temperatures ranging from 300 to 500 °C in steps of 100 °C by using rapid thermal annealing equipment in oxygen. The thicknesses of the films were observed by field emission scanning electron microscopy (FE-SEM); their grain size was calculated from the X-ray diffraction (XRD) spectra using the Scherrer equation. XRD measurements showed the AZO films to be crystallized with strong (002) orientation as substrate temperature increases over 300 °C. Their electrical properties were investigated by using the Hall measurement and their transmittance was measured by UV-vis spectrometry. The AZO film annealed at the 500 °C in oxygen showed an electrical resistivity of 2.24 × 10^− 3 Ω cm and a very high transmittance of 93.5% which were decreased about one order and increased about 9.4%, respectively, compared with as-deposited AZO film.     

Preparation and characterization of highly (1 1 1)-oriented (Pb,La)(Zr,Ti)O3 thin films by sol-gel processing

Lanthanum modified lead zirconate titanate (Pb_0.91La_0.09)(Zr_0.65Ti_0.35)O₃ (PLZT) ferroelectric thin films were grown on Pt/Ti/SiO₂/Si(1 0 0) and fused quartz substrates using a sol-gel method with rapid thermal annealing processing. The results showed that the highly (1 1 1)-oriented pervoskite PLZT thin film growth on Pt/Ti/SiO₂/Si(1 0 0) substrates. The electrical measurements were conducted on PLZT films in metal-ferroelectric-metal capacitor configuration. The PLZT thin films annealed at 600 °C showed well-saturated hysteresis loops with remanent polarization and coercive electric field values were 10.3 μC/cm² and 36 kV/cm, respectively, at an applied field of 300 kV/cm. At 100 kHz, the dielectric constant and dielectric loss of the film are 682 and 0.021, respectively. The PLZT thin film on fused quartz substrate, annealed at 600 °C, exhibited good optical transmittance, the band gap of optical direct transitions is 3.89 eV.     

Influence of annealing treatments for ZnO-doped Zr0.8Sn0.2TiO4 thin films by RF magnetron sputtering

Zirconium tin titanium oxide doped 1 wt.% ZnO thin films on n-type Si substrate were deposited by rf magnetron sputtering at a fixed rf power of 300 W, a substrate temperature of 450 °C, a deposition pressure of 5 mTorr and an Ar/O₂ ratio of 100/0 with various annealing temperatures and annealing times. Electrical properties and microstructures of 1 wt.% ZnO-doped (Zr_0.8Sn_0.2)TiO₄ thin films prepared by rf magnetron sputtering on n-type Si(100) substrates at different annealing temperatures (500 °C-700 °C) and annealing times (2 h-6 h) have been investigated. The structural and morphological characteristics analyzed by X-ray diffraction (XRD) and atomic force microscope (AFM) were sensitive to the treatment conditions such as annealing temperature and annealing time. At an annealing temperature of 600 °C and an annealing time of 6 h, the ZnO-doped (Zr_0.8Sn_0.2)TiO₄ thin films possess a dielectric constant of 46 (at f = 10 MHz), a dissipation factor of 0.059 (at f = 10 MHz), and a low leakage current density of 3.8 × 10^− 9 A/cm² at an electrical field of 1 kV/cm.     

Properties of transparent conducting oxides formed from CdO alloyed with In2O3

The structure, optical and electrical properties of transparent conducting oxide films depend greatly on the methods of preparation, heat treatment, type and level of dopant. Thin films of (CdO)_1−x(In₂O₃)_x have been grown by electron beam evaporation technique for different concentrations of In₂O₃ (x = 0, 0.05, 0.1, 0.15 and 0.2). Increase of doping led to increased carrier concentration as derived from optical data and hence to increased electrical conductivity, which degraded the transparency of the films. An improvement of the electrical and optical properties of Cadmium indium oxide (CdIn₂O₄) has been achieved by post-deposition annealing. A resistivity value of 7 × 10^− 5 Ω cm and transmittance of 92% in the near infrared region and 82% in the visible region have been obtained after annealing at 300 °C for 90 min in air.     

An investigation of super-hydrophilic properties of TiO2/SnO2 nano composite thin films

A sol-gel dip coating technique was used to fabricate TiO₂/SnO₂ nano composite thin films on soda-lime glass. The solutions of SnO₂ and TiO₂ were mixed with different molar ratios of SnO₂:TiO₂ as 0, 3, 4, 6, 8, 9, 10.5, 13, 15, 19.5, 25 and 28 mol.% then the films were prepared by dip coating of the glasses. The effects of SnO₂ concentration, number of coating cycles and annealing temperature on the hydrophilicity of films were studied using contact angle measurement. The films were characterized by means of scanning electron microscopy, X-ray diffraction and atomic force microscopy measurements. The nano composite thin films fabricated with 8 mol.% of SnO₂, four dip coating cycles and annealing temperature of 500 °C showed super-hydrophilicity.     

Indium tin oxide films made from nanoparticles: models for the optical and electrical properties

Porous thin films comprising nanoparticles of In₂O₃:Sn (known as indium tin oxide, ITO) were made by spin coating followed by annealing. The nanoparticles were prepared by a wet chemical technique. The films had a luminous transmittance of ∼90% and an electrical resistivity of ∼10⁻² Ω cm. Spectral transmittance and reflectance were analyzed by first representing the ITO nanoparticles within the Drude theory, with a frequency-dependent scattering time characteristic for ionized impurity scattering, and then applying effective medium theory to account for the porosity. It was found that the individual nanoparticles had a resistivity of ∼2×10⁻⁴ Ω cm, i.e. their electrical properties were comparable to those in the best films made by physical or chemical vapour deposition. Temperature-dependent electrical resistivity data for the films could be reconciled with a model for fluctuation induced tunneling between micrometer-size clusters of internally connected ITO nanoparticles.     

Effects of heat treatment on properties of ITO films prepared by rf magnetron sputtering

Indium tin oxide (ITO) films were deposited on glass substrates by rf magnetron sputtering using a ceramic target (In₂O₃-SnO₂, 90-10 wt%) without extra heating. The post annealing was done in air and in vacuum, respectively. The effects of annealing on the structure, surface morphology, optical and electrical properties of the ITO films were studied. The results show that the increase of the annealing temperature improves the crystallinity of the films, increases the surface roughness, and improves the optical and electrical properties. The transmittance of the films in visible region is increased over 90% after the annealing process in air or in vacuum. The resistivity of the films deposited is about 8.125×10⁻⁴ Ω cm and falls down to 2.34×10⁻⁴ Ω cm as the annealing temperature is increased to 500°C in vacuum. Compared with the results of the ITO films annealed in air, the properties of the films annealed in vacuum is better.     

Thin gold films on SnO2:In: Temperature-dependent effects on the optical properties

Gold films with thicknesses of 5 ± 0.5 nm were sputter deposited onto SnO₂:In-coated glass kept at different temperatures up to 140 °C, and similar films, deposited onto substrates at 25 °C, were annealing post treated at the same temperatures. Nanostructures and optical properties were recorded by scanning electron microscopy and spectrophotometry in the 0.3 to 2.5 μm wavelength range, respectively. Annealing had a minor influence on the optical transmittance despite significant changes in the scale of the nanostructure, whereas deposition onto substrates heated to 140 °C yielded granular films with strong plasmon absorption of luminous radiation. These results are of considerable interest for optical devices with gold films prepared at elevated temperature or operating at such temperature.     

Effects of annealing temperature on microstructure and electrical properties of Mn-Co-Ni-O thin films

Mn_1.85Co_0.3Ni_0.85O₄ (MCN) thin films were prepared on Al₂O₃ substrates by chemical solution deposition method at different annealing temperature (650, 700, 750 and 800 °C). Effects of annealing temperature on microstructure and electrical properties of MCN thin films were investigated. The MCN thin film annealed at 750 °C is of good crystallization and compact surface. It shows lower resistance (4.8 MΩ) and higher sensitivity (3720.6 K) than those of other prepared films. It also has small aging coefficient (3.7%) after aging at 150 °C for 360 h. The advantages of good properties make MCN thin film very promising for integrated devices.     

The effect of nitrogen on the properties of zinc nitride thin films and their conversion into p-ZnO:N films

Zinc nitride thin films were deposited by magnetron sputtering using ZnN target in plasma containing either N₂ or Ar gases. The rf-power was 100 W and the pressure was 5 mTorr. The properties of the films were examined with thermal treatments up to 550 °C in N₂ and O₂ environments. Films deposited in Ar plasma were opaque and conductive (ρ ∼ 10^− 1 to 10^− 2 Ω cm, N_D ∼ 10¹⁸ to 10²⁰ cm^− 3) due to excess of Zn in the structure. After annealing at 400 °C, the films became more stoichiometric, Zn₃N₂, and transparent, but further annealing up to 550 °C deteriorated the electrical properties. Films deposited in N₂ plasma were transparent but very resistive even after annealing. Both types of films were converted into p-type ZnO upon oxidation at 400 °C. All thermally treated zinc nitride films exhibited a shoulder in transmittance at around 345 nm which was more profound for the Ar-deposited films and particularly for the oxidized films. Zinc nitride has been found to be a wide band gap material which makes it a potential candidate for transparent optoelectronic devices.