SnO2 Thin Films Research Articles

Ultra‐Low Power Photosynaptic Devices Based on Persistent Photoconductivity‐Modulated SnO2

AbstractRealizing visual perception performance using robust metal oxide devices is highly desirable for brain‐inspired neuromorphic computing, visual prosthetics, and artificial intelligence. SnO2, a representative transparent semiconductor, has attracted considerable attention for its potential in ultraviolet photodetectors and photosynaptic devices operating in solar‐blind spectral ranges. This problem has been circumvented by lowering the electron concentration and reducing the persistent photoconductivity (PPC), one of the essential properties of photosynaptic devices. In this case, the electron concentration and PPC properties in SnO2 must be controlled independently. This paper reports the successful control of PPC in SnO2 by controllable addition of Zn and Sr ions, which act as acceptors to annihilate the charge carriers and as a reductant to form oxygen vacancies, respectively. Zn and Sr‐added SnO2 exhibits superior synaptic performance with low energy consumption, successfully imitating the biological synapses without a gate electrode. As a result, the PPC remains at about 40% even after 20 seconds of turning off the ultraviolet light, and energy consumption is reduced to 1–10 fJ, similar to energy consumption with biological synapses. A novel optical sensor that can receive analog signals is demonstrated using a photosynaptic device with Zn and Sr‐added SnO2 thin films.

Impact of NiO nanoparticle decoration on the surface of SnO2 thin films for gas sensing

Impact of NiO nanoparticle decoration on the surface of SnO2 thin films for gas sensing

Effect of experimental conditions on the fabrication of SnO2 thin films via spray pyrolysis technique

Effect of experimental conditions on the fabrication of SnO2 thin films via spray pyrolysis technique

Structure and Properties of Thin Films Prepared on Flexible Substrates from SnCl4-Derived Solutions

Thin transparent films of SnO2 were obtained from aqueous–alcohol solutions of SnCl4 on a flexible polyethylene terephthalate (PET) substrate by spray pyrolysis at 100 °C. The influence of the addition of aqueous ammonia to the film-forming solution on the different properties has been studied. Properties studied include surface morphology, phase composition and transparency of the formed films and the crystallization processes and band gap of the film material. It was found that the addition of aqueous ammonia causes the formation of skeletal crystals (NH4)2[SnCl6] with a perovskite structure in the film structure. The resulting films are promising for use in the technology of manufacturing flexible solar cells.

High Sensitivity Of Nanocrystalline SnO2-Y2O3 Thin Films Based UV-Detector Prepared Using Chemical Bath Deposition

Nanocrystalline Tin dioxide - Yttrium oxide (NC SnO2-Y2O3) thin film was effectively created by employing the chemical bath deposition approach on SiO2/Si substrates. X-ray diffraction, field emission scanning electron microscopy [FESEM], and energy-dispersive X-ray spectroscopy were used to analyze the structural and the surface morphology of the annealed sample at 500°C for two hours in air. When annealed at 500°C, the SnO2-Y2O3 film crystallized was accomplished with a tetragonal rutile structure. The nanocrystalline SnO2 thin film was effectively employed as a UV photodetector device (UV PDs). A UV photo detector based on nanocrystalline SnO2-Y2O3 film showed 2988% sensitivity when exposed to a 360 nm wavelength (6 mW/cm2) at an applied voltage of 3 V. In contrast, the responsivity value was 3.247 A/W. The rise and full times were determined by calculating to be 0.663 s and 0.436 s, respectively. The excellent performance of the device could be correlated with high surface-to-volume proportions including its elevated crystal performance. Given its outstanding stability and reliability, the nanocrystalline SnO2-Y2O3 thin film sensor is the optimum option for commercially photo-electronic applications.

Facile assembly of SnO2 thin film-based Al/SnO2/Al device for sensing of 260 nm UVC and 365 nm UVA radiation

An Al/SnO2/Al metal-semiconductor-metal (MSM) device was formed by depositing a ~55nm thin film of SnO2 on Si substrate. Structural, surface morphology and optical properties of the SnO2 film were studied. The current-voltage (I-V) characteristics of the device were recorded under the dark condition followed by 260 nm-UVC and 365 nm-UVA illumination conditions. Under the dark condition, the device shows a resistivity of 8.05 Ωcm at V=1.5V bias voltage. The device produces nearly symmetric rectifying-type I-V characteristics under forward and reverse bias conditions. The electrical properties of the device were explained using back-to-back Schottky diode model. Under the dark condition, the ideality factor of the junction under forward and reverse bias were estimated to be 1.08 and 1.72 respectively. The external quantum efficiency of the device under UVC was found to be ~518.72% and specific detectivity reached as high as 1.03×109 Jones at 2.0V with a response time of ~1s. The device showed a high signal-to-noise ratio between 0.5 and 1.5V bias voltages. The values of the ideality factor being greater than 1 was attributed to the presence of point defects in the SnO2 layer as verified by photoluminescence study. This study reveals that the device could be used as a UVC and UVA sensor at a relatively low bias voltage of ~1.5V.

Optical and nonlinear characterization of Er-doped SnO2 thin films fabricated by thermal evaporation: potential for advanced optical device applications

Optical and nonlinear characterization of Er-doped SnO2 thin films fabricated by thermal evaporation: potential for advanced optical device applications

Effect of Post-annealing Temperature on Microstructural, Morphological and Optical Properties of Sol–gel Spin Coated Cu Doped SnO2 Thin Films

Effect of Post-annealing Temperature on Microstructural, Morphological and Optical Properties of Sol–gel Spin Coated Cu Doped SnO2 Thin Films

Experimental and theoretical studies of sputter deposited pure SnO2 thin films for high selective and humidity-tolerant H2 gas sensor

Experimental and theoretical studies of sputter deposited pure SnO2 thin films for high selective and humidity-tolerant H2 gas sensor

Optimizing the resistivity of colloidal SnO2 thin films by ion implantation and annealing

Tin oxide (SnO2) is a critical material for a wide range of applications, such as in perovskite solar cells, gas sensors, as well as for photocatalysis. For these applications the transparency to visible light, high availability, cheap fabrication process and high conductivity of SnO2 benefits its commercial deployment. In this paper, we demonstrate that the resistivity of widely colloidal SnO2 can be reduced by noble gas ion beam modification. After low energy argon implantation with a fluence of 4×1015 at.cm−2 at 25keV and annealing at 200°C in air, the resistivity of as-deposited film was reduced from (178±6)μΩcm to (133±5)μΩcm, a reduction of 25%. Hall effect measurements showed that the primary cause of this is the increase in carrier concentration from (8.1±0.3)×1020 cm−3 to (9.9±0.3)×1020 cm−3. Annealing at 200°C resulted in the removal of defect clusters introduced by implantation, while annealing at 300°C resulted in the oxidation of the films, increasing their resistivity. The concentration of oxygen vacancy defects can be controlled by a combination of low energy noble gas ion implantation and annealing, providing promising performance increases for potential applications of SnO2 where a low resistivity is crucial.

Growth of Ta-doped SnO2 on GaN as a UV-transparent conducting electrode and band alignment properties of the heterojunction

GaN-based ultraviolet light emitting diodes (UV LEDs) have attracted considerable attention in recent years and are required in various applications such as healthcare, light illumination, and optical communication. However, the limited UV transparency of the electrodes like indium-doped tin oxide has hindered the external quantum efficiency of current UV LEDs. In this work, we present the growth of UV-transparent Ta-doped SnO2 (TTO) thin films on GaN as a promising UV-transparent electrode for LEDs. TTO thin films with a thickness of 200 nm exhibit optical transmission exceeding 80% at the wavelength of 300 nm, with a low resistivity of 2.5 × 10−4 Ω·cm and a low contact resistance of 1.7 × 10−2 Ω cm2 to n-type GaN. High-resolution x-ray photoemission spectra were employed to reveal insight into the electronic structure of TTO and the interfacial band alignment of TTO/GaN heterojunction. The wide optical bandgap (∼4.6 eV) and high UV transparency of TTO films stem from a significant Burstein–Moss shift due to degenerate doping, giving rise to metal-like characteristics and a small barrier height at the interface of TTO/GaN. These findings imply the origin of low contact resistivity of TTO to n-type GaN and may be applicable to the development of UV-transparent electrodes of optoelectronic devices.

Optical and electric properties of tin oxide (SnO2) with reduced graphene oxide nanocomposite thin films

Due to their superior properties, two-dimensional (2D) nanomaterial materials have become increasingly popular for enhancing SnO2 thin films. In the paper, a thermionic vacuum arc (TVA) deposition system was used to produce a thin film of SnO2 with a reduced graphene oxide (rGO) nanocomposite. SnO2 thin films have become widely used in sensor applications, and these sensors have been shown to work at relatively high temperatures compared to room-temperature semiconductors. As a result, working temperatures affect the material properties. The surface properties of the deposited and post-annealed samples were investigated using field emission scanning electron microscopy integrated with energy dispersive x-ray spectroscopy and atomic force microscopy. The weight ratios of carbon and tin were calculated as 35 % and 65 %, respectively. The mean Z-height of the nanoparticles was determined to be 9 nm, and the distribution of the surface grains is nearly homogeneous. Following the post-annealing process, the thin film's band gap energy decreased from 3.78 eV to 3.25 eV. According to the photoluminescence spectra, emission peaks at 393 nm, 406 nm, and 443 nm were measured. The transmittance spectra of the various post-annealed samples at 150 °C were recorded, and they remained nearly the same. This consistency is a beneficial property of the thin film because SnO2:rGO nanocomposite thin films are designed to operate at relatively high temperatures. The present study investigates the advantages and properties of the post-annealed (repeating annealing) SnO2: rGO thin film.

Enhancing the Performance of Nanocrystalline SnO2 for Solar Cells through Photonic Curing Using Impedance Spectroscopy Analysis.

Wide-bandgap tin oxide (SnO2) thin-films are frequently used as an electron-transporting layers in perovskite solar cells due to their superior thermal and environmental stabilities. However, its crystallization by conventional thermal methods typically requires high temperatures and long periods of time. These post-processing conditions severely limit the choice of substrates and reduce the large-scale manufacturing capabilities. This work describes the intense-pulsed-light-induced crystallization of SnO2 thin-films using only 500 μs of exposure time. The thin-films' properties are investigated using both impedance spectroscopy and photoconductivity characteristic measurements. A Nyquist plot analysis establishes that the process parameters have a significant impact on the electronic and ionic behaviors of the SnO2 films. Most importantly, we demonstrate that light-induced crystallization yields improved topography and excellent electrical properties through enhanced charge transfer, improved interfacial morphology, and better ohmic contact compared to thermally annealed (TA) SnO2 films.

Formation of metallic/oxide composites of Sn from SnO2 thin films with swift heavy ion irradiation

Formation of metallic/oxide composites of Sn from SnO2 thin films with swift heavy ion irradiation

Structural and optical study of RF-magnetron sputtering SnO2 thin films: impact of post annealing temperature

Tin oxide (SnO2) thin films are prepared using radio frequency magnetron sputtering (RF) method and then annealed at different temperatures in the range of 550–750 °C for 1 h. The effects of annealing temperature on the structural and optical properties of the films are investigated using x-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and spectrophotometer. It is evident that the annealed films have flat surface with smooth morphology. Based on the XRD graph, as deposited films were amorphous and the annealed films had polycrystalline nature and contain the SnO2 tetragonal rutile phase. According to Raman spectra, the annealed films revealed three vibration modes Eg, A1g and B2g at the frequencies of Sn-O bond vibrations, which related to the SnO2 phase. The samples exhibit an average optical transmittance with more than 80 % between 400 − 700 nm. The refractive index values were in the range of 0.9-2.4 at visible wavelength. It is found that with increasing annealing temperature the films become more transparence while the refractive index and the extinction coefficient increased. The optical band gap energy decreases with increasing annealing temperature that means that the optical quality of annealed films is improved.

Impact of evolution of structural defects on the ferromagnetic and electrical properties of laser deposited Indium-doped SnO2 thin films

Impact of non-magnetic cationic-substitution on the evolution of structural defects and correlated ferromagnetic and electrical properties are investigated in series of pulsed laser deposited Sn1-xInxO2 (0.0 ≤ x ≤ 0.12) thin films. Beyond the nominal doping concentration of 2 at.% (i.e. x > 0.02), Indium (In)-doped SnO2 film switches to exhibit from n-type to p-type electrical conductivity and simultaneously the magnetization (MS) as well as the Curie temperature (TC) of the films increase significantly. Estimated values of ‘MS’ and ‘TC’ are found to achieve as large as 15.21 emu/cm3 and 540 K respectively when In-doping concentration approaches towards x = 0.08 and afterwards tend to decrease abruptly. Various spectroscopic techniques including Positron Annihilation Lifetime Spectroscopy (PALS) have detected the existence of Sn vacancy (VSn) defects within Sn1-xInxO2 films arise as the effect of In-substitution at Sn site (InSn) under O-rich atmosphere. The estimated positron lifetimes and the increase of line-shape S-parameter confirm the rise of VSn defects which serve as the major source of magnetic moments in non-magnetic host SnO2. Besides, InSn defects introduce excess holes within SnO2 lattice and thereby the magnetic spin-spin RKKY interaction between near-by VSn defects are mediated ferromagetically through the localized holes. For x > 0.08, stabilization of various donor-type defects such as Sn interstitial (Sni), indium interstitial (Ini) actually compensates the acceptors that leads to reduce the effective hole density consequently diminishing the strength of ferromagnetism within SnO2. Hence, tuning of such ferromagnetic and semiconducting properties through non-magnetic cationic substitution in transparent conducting oxides can be very promising in the field of next-generation spintronics.

Impact of In-doping and post-annealing on the properties of SnO2 thin films deposited by magnetron sputtering

SnO2 is a transparent semiconductor that has shown versatile applications in various fields. This study investigates the impact of In-incorporation and post-annealing on the structural, optical and electronical properties of SnO2 thin films deposited via RF magnetron sputtering. Three SnO2 target compositions were employed, with one unintentionally doped (UID), one with 1.0 at% In, and the other with 18.2 at% In. UV–vis spectroscopy reveals the presence of band tails in the as-deposited films, which can be significantly suppressed through annealing, particularly in air. Oxygen vacancy-related defect states below the conduction band minimum are believed to be responsible. Further, film thicknesses, refractive indices, and absorption coefficients were estimated from the UV–vis spectra of the films, employing the irritative Swanepoel method. The resistivities of SnO2:In films exhibit parabolic trends with respect to annealing temperature with minima values at 300 °C, while that of UID-SnO2 increases monotonically. P-type conductivity was found in the 300 °C-annealed SnO2:18.2 at% In films both in air and N2, with the N2-annealing leading to higher mobility (162.7 cm2·V−1·s−1) and lower resistivity (0.57 Ω·cm). The Fermi levels of the SnO2:In films are found to locate deep inside the bandgap, which is beneficial to form homojunctions with SnO2 of shallow Fermi levels.

Enhancing photo-response performance through ultrathin Al2O3 modification at the p-SnO2:Al/n-GaN heterojunction interface

We report on photoconductive and p-n heterojunction ultraviolet (UV) photodetectors based on p-type Al-doped SnO2 (p-SnO2:Al) thin films. We investigated the structural, optical, and electrical properties of Al-doped SnO2 thin films prepared using sol-gel methods, with our results being strongly supported by first-principles calculations. To achieve a self-powered photodetector device at zero bias, we fabricated p-SnO2:Al thin film on an n-GaN layer to form a p-n heterojunction. The responsivity of the p-n heterojunction UV detector, measured at zero bias, is 0.05 A/W, indicating good rectification properties. In order to improve device performance, a p-n heterojunction with a passivation layer was formed by inserting an ultrathin Al2O3 layer between the n-GaN layer and the p-SnO2:Al layer. With this change, the device's responsivity was 0.44 A/W at 350 nm at zero bias, roughly 10 times better than the detector without the Al2O3 passivation layer. The insertion of an ultrathin Al2O3 layer, which increases the efficiency of carrier separation on the SnO2 side while lowering the rate of carrier recombination at the interface, is responsible for the increased light responsivity performance.

Composites electron transport layer of PVA-regulated SnO2 for high-efficiency stable perovskite solar cells

As a new and efficient solar cell, perovskite solar cell has attracted wide attention due to its excellent performance. The electron transport layer in perovskite solar cells has a significant impact on device performance. SnO2 films that can be prepared by solution method have become the first choice for electron transport layer due to their simple process and excellent performance. However, the defects in SnO2 thin films and non-radiative recombination sites at the SnO2/Perovskite interface will lead to potential losses in the performance of photovoltaic devices. Therefore, in order to improve the interface loss and interface characteristics and prepare more efficient perovskite solar cells. In this work, a functional polymer, polyvinyl alcohol (PVA), is introduced to regulate the arrangement of SnO2 nanocrystals. The SnO2-PVA composite electron transport layer not only improves carrier transport, but also further affects the growth of perovskite films. PVA inhibits the agglomeration of tin dioxide particles by adding it to the aqueous solution of tin dioxide. Meanwhile, the oxygen vacancy defects in the SnO2 layer have also improved. Correspondingly, SnO2-PVA-based PSCs can be obtained a maximum efficiency of 23.73 %. Attributed to the strengthened interface binding and the improved perovskite crystallization process, the devices obtain good long-term stability, retaining 90 % of their initial performance after 1000 h operation at their maximum power point under 1 sun illumination.

Efficiency improvement of antimony selenide solar cells based on S-doped SnO2 buffer layer

Antimony Selenide (Sb2Se3) exhibits potential as a solar energy material owing to its optimal bandgap, lack of toxicity, and abundance of earth abundant elements. Currently, cadmium sulfide (CdS) serves as the predominant buffer layer for Sb2Se3 solar cells. However, the use of CdS hinders environmentally friendly advancement due to the toxic properties of the element cadmium. Hence, the quest for non-toxic buffer layers poses a significant challenge to the further advancement of Sb2Se3 solar cells. In prior research, tin oxide (SnO2) has been explored as a buffer layer. Nonetheless, the efficiency of SnO2/Sb2Se3 solar cells was hampered by the rough surface of SnO2 films and the poor crystallinity of Sb2Se3 films. In this investigation, we enhanced device efficiency by improving the uniformity of the SnO2 surface and enhancing the crystallinity of Sb2Se3 through spin-coating sulfur (S) onto the SnO2 film. Detailed examinations were conducted on the structure, optical, and electrical properties of the respective SnO2 and Sb2Se3 thin films. Ultimately, an efficiency of 3.38% was achieved using the spin-coated S:SnO2 film, marking an 85% enhancement compared to the baseline device.