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.     

Dielectric and ferroelectric properties of Ba(Sn0.15Ti0.85)O3 thin films grown by a sol-gel process

Ferroelectric Ba(Sn_0.15Ti_0.85)O₃ (BTS) thin films were deposited on LaNiO₃-coated silicon substrates via a sol-gel process. Films showed a strong (1 0 0) preferred orientation depending upon annealing temperature and concentration of the precursor solution. The dependence of dielectric and ferroelectric properties on film orientation has been studied. The leakage current density of thin films at 100 kV/cm was 7 × 10⁻⁷ A/cm² and 5 × 10⁻⁵ A/cm² and their capacitor tunability was 54 and 25% at an applied field of 200 kV/cm (measurement frequency of 1 MHz) for the thin films deposited with 0.1 and 0.4 M spin-on solution, respectively. This work clearly reveals the highly promising potential of BTS compared with BST films for application in tunable microwave devices.     

Temperature effects on the optoelectronic properties of AgIn5S8 thin films

Polycrystalline AgIn₅S₈ thin films are obtained by the thermal evaporation of AgIn₅S₈ crystals onto ultrasonically cleaned glass substrates under a pressure of ~ 1.3 × 10⁻³ Pa. The temperature dependence of the optical band gap and photoconductivity of these films was studied in the temperature regions of 300-450 K and 40-300 K, respectively. The heat treatment effect at annealing temperatures of 350, 450 and 550 K on the temperature dependent photoconductivity is also investigated. The absorption coefficient, which was studied in the incidence photon energy range of 1.65-2.55 eV, increased with increasing temperature. Consistently, the absorption edge shifts to lower energy values as temperature increases. The fundamental absorption edge which corresponds to a direct allowed transition energy band gap of 1.78 eV exhibited a temperature coefficient of −3.56 × 10⁻⁴ eV/K. The 0 K energy band gap is estimated as 1.89 eV. AgIn₅S₈ films are observed to be photoconductive. The highest and most stable temperature invariant photocurrent was obtained at an annealing temperature of 550 K. The photoconductivity kinetics was attributed to the structural modifications caused by annealing and due to the trapping-recombination centers' exchange.     

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.     

Growth of crystalline HgCr2S4 thin films at mild reaction conditions

Thin films of crystalline HgCr₂S₄ have been deposited on glass substrates at low temperature as low as 65 °C using a chemical bath deposition method. Typical thickness of the deposited HgCr₂S₄ thin films was 264 nm.The films were composed of closely packed irregular grains of 165-175 nm in diameter. The X-ray diffraction analysis and the selected area electron diffraction analysis revealed the deposited thin films were polycrystalline with highly (2 2 0) preferential orientation. The films exhibit a pure faint black. Their direct band gap energy was 2.39 eV with room temperature electrical resistivity of the order of 10⁻³ Ω cm.     

Structural,optical and electrical properties of In4Sn3O12 films prepared by pulsed laser deposition

Highly conducting (σ ∼ 2.6 × 10³ Ω⁻¹ cm⁻¹) In₄Sn₃O₁₂ films have been deposited using pulsed laser deposition (PLD) on glass and quartz substrates held at temperatures between 350 and 550 °C under chamber pressures of between 2.5 and 15 mTorr O₂. The crystallinity and the surface roughness of the films were found to increase with increasing substrate temperature. Electron concentrations of the order of 5 × 10²⁰ cm⁻³ and mobilities as high as 30 cm² V⁻¹ s⁻¹ were determined from Hall effect measurements performed on the films. Fitting of the transmission spectral profiles in the ultra-violet–visible spectrum has allowed the determination of the refractive index and extinction coefficient for the films. A red-shift in the frequency of plasmon resonance is observed with both increasing substrate temperature and oxygen pressure. Effective masses have been derived from the plasma frequencies and have been found to increase with carrier concentration indicating a non-parabolic conduction band in the material In₄Sn₃O₁₂. The optical band-gap has been determined as 3.8 eV from the analysis of the absorption edge in the UV. These results highlight the potential of these films as lower In-content functional transparent conducting materials.     

Laser annealing of Pb(Zr0.52Ti0.48)O3 thin films for the pyroelectric detectors

Lead zirconate titanate (Pb(Zr_0.52Ti_0.48)O₃, PZT) thin films fabricated by magnetron sputtering technique on the Pt/Ti/SiO₂/Si substrates at room temperature, were annealed by means of CO₂ laser with resulting average substrate temperature below 500 °C. The crystal structure, surface morphology and pyroelectric properties of the PZT films before and after annealing were investigated by X-ray diffraction, atomic force microscopy, and pyroelectric measurements. The results show that the annealed PZT thin film with a laser energy density of 490 W/cm² for 25 s has a typical perovskite phase, uniform crystalline particles with a size of about 90 nm, and a high pyroelectric coefficient with 1.15 × 10^− 8 Ccm^− 2 K^− 1.     

Cathodoluminescence of CaWO4 and SrWO4 thin films prepared by spray pyrolysis

Thin films of CaWO₄ and SrWO₄ were prepared on glass substrates by spray pyrolysis. The effects of preparation conditions and monovalent, bivalent and trivalent cation doping on cathodoluminescence (CL) properties of the films were studied. Polycrystalline CaWO₄ and SrWO₄ films formed a scheelite structure after being annealed above 300°C. They exhibited analogous cathodoluminescence consisting of a blue emission band at 447 nm and a blue-green emission band at 487 nm. The blue and blue-green emission intensities increased with substrate and annealing temperature. Annealing atmosphere and doping with Ag⁺, Pb²⁺ and La³⁺ did not influence the characteristics of the blue and blue-green emissions, whereas Eu³⁺ did. The results indicated both the blue and blue-green emissions originated from the WO₄²⁻ molecular complex. The luminance and efficiency for CaWO₄ film were 150 cd/m² and 0.7 lm/W at 5 kV and 57 μA/cm².     

Composition, surface morphology and electrical characteristics of Al2O3-TiO2 nanolaminates and AlTiO films on silicon

We propose and demonstrate Metal-Oxide-Semiconductor structures comprising Al₂O₃-TiO₂ nanolaminate and AlTiO films. Composition, structural and electrical characteristics were studied in detail and compared to TiO₂ thin film-based structures. All dielectric films were evaporated using an electron beam gun (EBG) system on unheated p-Si substrate without adding O₂. MOS structures were investigated in detail before and after annealing at up to 950 °C in O₂ and N₂ + O₂ environments. The nanolaminate films remain in an amorphous state after annealing at 950 °C. The smallest quantum mechanical corrected equivalent oxide thickness measured was ∼1.37 nm. A large reduction of the leakage current density to 1.8 × 10^− 8 A/cm² at an electric field of 2 MV/cm was achieved by the annealing process.     

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.     

Structural and electrical properties of BiFeO3 thin films by solution deposition and microwave annealing

Lead-free polycrystalline BiFeO₃ (BFO) thin films were developed using a chemical solution deposition method to deposit the films and the multi-mode 2.45 GHz microwave furnace to optimize the annealing condition of the films. Phase-pure BFO films were obtained at 500 °C-600 °C for 1-5 min with a heating rate of 10 °C/min. The film by microwave annealing (MW) at 550 °C for 5 min exhibited a (012)-preferred orientation with a dense morphology of grain size ~ 294 nm. Its dielectric constant of 96.2, low leakage current density of 2.466 × 10^− 6 A/cm², polarization (2P_r) and coercive field (2E_c) of 0.931 μC/cm² and 57.37 kV/cm, respectively, were improved compared to those by conventional annealing (CA) at the same annealing conditions.     

A comparative study of the properties of thermally evaporated CuIn2n + 1S3n + 2 (n = 0, 1, 2 and 3) thin films

CuInS₂, CuIn₃S₅, CuIn₅S₈ and CuIn₇S₁₁ compounds were synthesized by the horizontal Bridgman method using high-purity copper, indium and sulphur elements. Crushed powders of these ingots were used as raw materials for the vacuum thermal evaporation. So, CuIn_2n + 1S_3n + 2 (n = 0, 1, 2, and 3) thin films were deposited by single source vacuum thermal evaporation onto glass substrates heated at 150 °C. The structural, compositional, morphological, electrical and optical properties of the deposited films were studied using X-ray diffraction (XRD), energy dispersive X-ray, atomic force microscopy and optical measurement techniques. XRD results revealed that all the films are polycrystalline. However, CuInS₂ and CuIn₃S₅ films had a chalcopyrite structure with preferred orientation along 112 while CuIn₅S₈ and CuIn₇S₁₁ films exhibit a spinel structure with preferred orientation along 311. The absorption coefficients of the all CuIn_2n + 1S_3n + 2 films are in the range of 10⁻⁴ and 10⁻⁵ cm⁻¹. The direct optical band gaps of CuIn_2n + 1S_3n + 2 layers are found to be 1.56, 1.78, 1.75 and 1.30 eV for n = 0, 1, 2, and 3, respectively. CuIn₃S₅ and CuIn₅S₈ films are p type with electrical resistivities of 4 and 12 Ω cm whereas CuInS₂ and CuIn₇S₁₁ are highly compensated with resistivities of 1470 and 1176 Ω cm, respectively.     

Structural and optical properties of amorphous and crystalline antimony sulfide thin-films

Smooth and compact thin films of amorphous and crystalline antimony sulfide (Sb₂S₃) were prepared by radio frequency sputtering of an Sb₂S₃ target. As-deposited films are amorphous. Polycrystalline antimony sulfide films composed of ∼ 500 nm grains are obtained by annealing the as-deposited films at 400 °C in sulfur vapors. Both amorphous and crystalline antimony sulfide have strong absorption coefficients of 1.8 × 10⁵ cm^− 1 at 450 nm and 7.5 × 10⁴ cm^− 1 at 550 nm, and have direct bandgaps with band energies of 2.24 eV and 1.73 eV, respectively. These results suggest the potential use of both amorphous and crystalline antimony sulfide films in various solid state devices.     

Microstructure and thermoelectric properties of Sn-doped Bi2Te2.7Se0.3 thin films deposited by flash evaporation method

(Bi_1 − xSn_x)₂Te_2.7Se_0.3 thermoelectric thin films with thickness of 800 nm have been deposited on glass substrates by flash evaporation method at 473 K. The structures, morphology of the thin films were analyzed by X-ray diffraction and field emission scanning electron microscopy respectively. Effects of Sn-doping concentration on thermoelectric properties of the annealed thin films were investigated by room-temperature measurement of Seebeck coefficient and electrical resistivity. The thermoelectric power factor was enhanced to 12.8 μW/cmK² (x = 0.003). From x = 0.004 to 0.01 Sn doping concentration, the Seebeck coefficients are positive and show p-type conduction. The Seebeck coefficient and electrical resistivity gradually decrease with increasing Sn doping concentration.     

Optical properties of nanocrystalline SnS2 thin films

Thin films of nanocrystalline SnS₂ on glass substrates were prepared from solution by dip coating and then sulfurized in H₂S (H₂S:Ar = 1:10) atmosphere. The films had an average thickness of 60 nm and were characterized by X-ray diffraction studies, scanning electron microscopy, EDAX, transmission electron microscopy, UV-vis spectroscopy, and Raman spectroscopy. The influence of annealing temperature (150-300 °C) on the crystallinity and particle size was studied. The effect of CTAB as a capping agent has been tested. X-ray diffraction analysis revealed the polycrystalline nature of the films with a preferential orientation along the c-axis. Optical transmission spectra indicated a marked blue shift of the absorption edge due to quantum confinement and optical band gap was found to vary from 3.5 to 3.0 eV with annealing temperature. Raman studies indicated a prominent broad peak at ∼314 cm⁻¹, which confirmed the presence of nanocrystalline SnS₂ phase.     

Observation of broadband infrared luminescence in a novel Bi-doped P2O5-B2O3-Al2O3 glass

A novel Bi-doped P₂O₅-B₂O₃-Al₂O₃ glass was investigated, and strong broadband NIR (near infrared) luminescence was observed when the sample was excited by 445 nm, 532 nm, 808 nm and 980 nm lasers, respectively. The max FWHM with 312 nm, the lifetime with 580 μs and the σ_emτ product with 5.3 × 10^− 24 cm² s were obtained which indicates that this glass is a promising material for broadband optical amplifier and tunable laser. The effect of the introduction of B₂O₃ on the glass structure and Bi-ions illuminant mechanism were discussed and analyzed. It is suggested that the introduction of B₂O₃ makes the glass structure closer, and the broadband NIR emission derives from Bi⁰:²D_3/2 → ⁴S_3/2 and Bi⁺:³P₁ → ³P₀ transitions.     

Chemically deposited lead sulfide and bismuth sulfide thin films and Bi2S3/PbS solar cells

Solar cells with a short-circuit current density (J_sc) of 6 mA/cm², an open circuit voltage (V_oc) of 280 mV and a conversion efficiency of 0.5% under a 1000 W/m² solar radiation were prepared by sequential chemical deposition of Bi₂S₂ (160 nm) and PbS (400 nm) thin films. The optical band gap (E_g) of Bi₂S₃ (160 nm) decreased from 1.67 to 1.61 eV upon heating the as-deposited film at 250 °C in air for 15 min to make it crystalline, but also reduced its thickness to 100 nm. Photoconductivity of this film is 0.003 (Ω cm)^− 1. The E_g of PbS film (200 nm) deposited at 25 °C (24 h) is 0.57 eV, and is 0.49 eV for the film deposited at 40 °C. The electrical conductivity of the latter is 0.48 (Ω cm)^− 1. The photo-generated current density for a Bi₂S₃(100 nm)/PbS(300 nm) absorber stack is above 40 mA/cm² under AM 1.5 G (1000 W/m²) solar radiation. However, the optical losses in the cell structure reduces the J_sc. Spectral sensitivity of the external quantum efficiency of the cell establishes the contribution of Bi₂S₃ and PbS to J_sc. The energy level diagram of the cell structure suggests a built-in potential of 470 mV for the present case. Six series-connected cells gave the V_oc of 1.4 V and J_sc of 5 mA/cm².     

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.     

An open-framework bimetallic chalcogenide structure K3Rb3Zn4Sn3Se13 built on a unique [Zn4Sn3Se16] cluster: synthesis, crystal structure, ion exchange and optical properties

Single crystals of K₃Rb₃Zn₄Sn₃Se₁₃ were synthesized by solvothermal method. The building block in this structure is a [Zn₄Sn₃Se₁₆]¹²⁻ cluster which consists of four ZnSe₄ and three SnSe₄ tetrahedra connected through corner-sharing of Se atoms. The 3D network contains intersecting channels running parallel to the crystallographic [2 1 1], [1-1-1] and [12-1] directions. The disordered K⁺ and Rb⁺ cations reside in these channels. Ion exchange of Cs⁺ with disordered Rb⁺/K⁺ ions in the structure showed a partial replacement of 15.8%. Optical diffuse reflectance experiments were carried out and gave a sharp absorption edge at 2.6 eV.