SnOx Thin Films Research Articles

Properties and electrical evolution of ambipolar SnOx thin films grown by atomic layer deposition in low temperature range

The ambipolar SnOx film is a promising substitution for organic material as hole transport or interconnection layer in perovskite devices, and low temperature process is essential to avoid the decomposition and thermal stress of the perovskite material. In this work, we prepared the ambipolar SnOx thin film via atomic layer deposition in low temperature range of 40–120 °C, and systematically investigated the surface morphology, wettability, chemical, optical and electrical properties. The obvious absorption band in near-infrared revealed the mid-gap band which contributes to the hole transport for SnOx films. The film displayed only hole transport behavior with the mobility of 1.25 × 10−3 cm2 v−1 s−1 at 40 °C, and achieved best ambipolar property at 100 °C with the electron mobility of 4.84 × 10−3 cm2 v−1 s−1 and the hole mobility of 1.15 × 10−3 cm2 v−1 s−1. This study provides a practical approach to manipulate the carrier transport behavior, chemical, and optical property of ALD SnOx thin film deposited in low temperature range, boosting their further exploration and high-performance development in different device structures which apply p-n junctions.

Investigation of diodic behavior in p-NiO/n-SnO2 bilayer heterojunctions fabricated via DC magnetron reactive sputtering

Tin oxide (SnOx) thin films at varying oxygen flow rates and Nickel oxide (NiO) thin films were deposited by reactive dc magnetron sputtering on glass substrates. Structural, chemical, morphological, optical and electrical properties of the deposited films were studied. XRD studies confirmed that the deposited films were polycrystalline in nature. SnOx thin films have shown two phases such as SnO and SnO2. AFM and SEM were used to analyse the morphology of the films and EDS confirmed the presence of Sn and Ni in the respective films. The examination of the x-ray photoelectron spectrum showed that the sputtered SnOx films contain both Sn2+ and Sn4+ oxidation states and NiO films contain Ni+2 and Ni+3 oxidation states. Photoluminescence study shows strong violet and weak red emission peaks for SnOx films and NiO showed strong emission peaks in the orange-red region. The optical results demonstrate that the films were transparent. The bandgap of SnOx and NiO samples were ∼3.3 eV and − 3.42 eV, respectively. Further we constructed a p-NiO/n-SnO2 heterojunction diode and its electrical characteristics were thoroughly assessed. Using dark current–voltage measurements, electrical characteristics such saturation current, ideality factor and barrier height were determined. The increase in oxygen flow rate led to reduction in the rectification of the devices. Our findings support the creation of high-performance metal oxide heterojunction for optoelectronic devices.

Room-temperature, RF-activated, quantum effects via engineered defect sites in thin-film AlN, Al2O3, and SnOx

The behavior of a sine wave propagated through thin films of aluminum nitride (AlN), aluminum oxide (Al2O3), and tin oxide (SnOx) with engineered buried defect sites may suggest quantum excitation and defect-mediated waveform modulations. Two distinct methods to induce these buried defects, etch pattern defects (EPD) and indentation pattern defects (IPD), were employed to detect these interactions. All the experiments were conducted at room temperature (21 °C) over a frequency range between 5 and 1000 kHz. In addition, EPD and IPD devices were composed of AlN, Al2O3, and SnOx. An inverse relationship between excitation frequency and voltage is observed for all devices. All these devices exhibited a relaxation time ranging between 0.2 and 0.75 µs. Devices without these engineered defect sites preserve the waveform integrity, emphasizing the impact of the buried defect sites. This research focuses on the relationship between defect type, excitation frequency, and voltage to understand the deeper mechanisms at play in these quantum defect-driven wave alterations in AlN, Al2O3, and SnOx thin films.

N-type and P-type SnOx thin films based MOX gas sensor testing

N-type and P-type SnOx thin films based MOX gas sensor testing

Tunable band-selective photodetector based on sputter-deposited SnOx thin-films: Effect of reactive gas pulsing process

In this work, high-performance SnOx band-selective photodetectors (PDs) were realized by DC magnetron sputtering technique. The reactive gas pulsing process (RGPP) was implemented with pulsing period fixed at P = 20 s to adjust tin and oxygen concentrations in the film. The impact of pulsed oxygen time on the structural, morphological and photosensing properties of SnOx-based PDs was investigated. The fabricated SnOx-based PD at a high duty cycle of 80% of P demonstrated high UV photodetection capabilities and solar-blind characteristic with a high responsivity of 21.8 mA/W, a high signal to noise ratio of 6 × 104 and a specific detectivity of about 5 × 1011 Jones. It was also revealed that the use of a short oxygen pulsing time 8 s paves the way for the realization of multispectral SnOx PD, demonstrating a high responsivity values of 36.45 mA/W, 36.4 mA/W and 34 mA/W over UV, Visible and NIR bands, respectively. This is attributed to the role of using RGPP in modulating the film optoelectronic properties from metallic to insulator when the duty cycle and thus oxygen concentration in the films changed from pure tin to overstoichiometric SnO2 compound. The prepared SnOx PDs demonstrated many advantageous features like low-noise, cost effective and high sensitivity. The obtained results proved that SnOx can be used as an alternative material for developing high-performance band-selective sensing devices.

Electrical Properties of a p‐SnOx/n‐SnOx Diode on a Flexible Polyimide Substrate

In recent years, flexible electronics have been an area of considerable interest due to the development of materials such as transparent semiconductor oxides, which are compatible with flexible substrates. Herein, lithography and magnetron sputtering are used to fabricate a flexible p–n diode of SnOx thin films on a polyimide substrate and electrical characterization is performed by varying the bending cycles. Using specific oxygen concentrations in the reactive gas mixture of the sputtering system, transparent p‐SnO0.8 (8.0% ppO2) and n‐SnO1.2 (18.5% ppO2) on polyimide substrates are successfully deposited. Electrical results show the SnOx diode exhibits a threshold voltage of 2.24 V and a great rectification ratio of 102. It is found the diode has excellent I–V rectifying behavior even when subjected to bending with a radius of curvature of 10 mm. It is important to note that after 200 bending cycles at a curvature radius of 50 mm, the p‐SnOx/n‐SnOx diode retains its rectifying behavior, making it attractive for large‐scale applications in transparent and flexible electronics.

Effects of rapid thermal annealing temperature on NO2 gas sensing properties of p-type mixed phase tin oxide thin films

Effects of the rapid thermal annealing (RTA) temperature on the NO2 gas sensing properties of p-type SnOX thin films were investigated. The SnOX thin films were deposited using radio-frequency magnetron sputtering and subjected to RTA at 200 °C, 250 °C, and 300 °C. The deposited SnOX thin films contained both p-type SnO and n-type SnO2 components, but the SnO was the dominant phase. The amount of SnO2 components increased with increasing RTA temperature, but the highest amount of oxygen vacancy (OVac) states was observed in the SnOX thin film annealed at 250 °C. The surface roughness of the SnOX thin film decreased as the RTA temperature increased. The SnOX thin film subjected to RTA at 250 °C exhibited a significantly higher maximum sensing response to NO2 (4.25–10 ppm NO2 at 60 °C) than those of the films treated at 200 °C (1.13) or 300 °C (0.92). The higher response was attributed to the larger amount of SnO2 and OVac in the thin film and large number of defects and cracks on the film surface. The experimental results demonstrated that the post-deposition RTA temperature considerably affects the NO2 sensing properties of the p-type SnOX-based gas sensors.

Room-Temperature Fabrication of p-Type SnO Semiconductors Using Ion-Beam-Assisted Deposition.

Over the past decade, SnO has been considered a promising p-type oxide semiconductor. However, achieving high mobility in the fabrication of p-type SnO films is still highly dependent on the post-annealing procedure, which is often used to make SnO, due to its metastable nature, readily convertible to SnO2 and/or intermediate phases. This paper demonstrates a fully room-temperature fabrication of p-type SnOx thin films using ion-beam-assisted deposition. This technique offers independent control between ion density, via the ion-gun anode current and oxygen flow rate, and ion energy, via the ion-gun anode voltage, thus being able to optimize the optical band gap and the hole mobility of the SnO films to reach 2.70 eV and 7.89 cm2 V-1 s-1, respectively, without the need for annealing. Remarkably, this is the highest mobility reported for p-type SnO films whose fabrication was carried out entirely at room temperature. Using first-principles calculations, we rationalize that the high mobility is associated with the fine-tuning of the Sn-rich-related defects and lattice densification, obtained by controlling the density and energy of the oxygen ions, both of which optimize the spatial overlap of the valence bands to form a continuous conduction path for the holes. Moreover, due to the absence of the annealing process, the Raman spectra reveal no significant signatures of microcrystal formation in the films. This behavior contrasts with the case involving the air-annealing procedure, where a complex interaction occurs between the formation of SnO microcrystals and the formation of SnOx intermediate phases. This interplay results in variations in grain texture within the film, leading to a lower optimum Hall mobility of only 5.17 cm2 V-1 s-1. Finally, we demonstrate the rectification characteristics of all-fabricated-at-room-temperature SnOx-based p-n devices to confirm the viability of the p-type SnOx films.

P-type conversion of distorted SnOx thin film by mild thermal annealing treatment in pure N2 environment

Tin oxide semiconductors can achieve both n- and p-type conduction, depending on the oxidation state of Sn. An n-type conduction can easily be fabricated; however, considerable optimization is required for fabrication of a p-type behavior. In this study, n-type SnOx thin films, prepared by reactive magnetron sputtering, were converted to p-type behavior using only post-deposition annealing at 600 °C in a pure nitrogen atmosphere. The annealing-temperature-dependent electrical properties of the SnOx thin films led to a remarkable increase in the yield of p-type behavior at 600 °C. X-ray diffraction analysis revealed that the SnOx film had a SnO2-dominant crystal phase and also suggested that N2 molecules dissociated at 600 °C and filled the oxygen vacancy (VO) site as atomic nitrogen. A detailed analysis of the binding state by x-ray photoelectron spectroscopy confirmed an increase in SnO-derived components, the appearance of peaks derived from N–Sn bonding, a decrease in VO caused by nitrogen doping, and charge transfer. Thus, we found that addition of nitrogen atoms promotes a chemical shift from Sn4+ to Sn2+ and that simultaneously passivates VO and contributes to hole generation.

Study of wide bandgap SnOx thin films grown by a reactive magnetron sputtering via a two-step method

In the present work, we report on the microstructural and optoelectronic properties of SnOx thin films deposited by a reactive radio frequency magnetron sputtering. After SnOx growth by sputtering under O2/Ar flow, we have used three different treatment methods, namely (1) as deposited films under O2/Ar, (2) vacuum annealed films ex-situ, and (3) air annealed films ex-situ. Effects of the O2/Ar ratios and the growth temperature were investigated for each treatment method. We have thoroughly investigated the structural, optical, electrical and morphology of the different films by several advanced techniques. The best compromise between electrical conductivity and optical transmission for the use of these SnOx films as an n-type TCO was the conditions O2/Ar = 1.5% during the growth process, at 250 °C, followed by a vacuum post thermal annealing performed at 5 × 10–4 Torr. Our results pointed out clear correlations between the growth conditions, the microstructural and optoelectronic properties, where highly electrically conductive films were found to be associated to larger grains size microstructure. Effects of O2/Ar flow and the thermal annealing process were also analysed and discussed thoroughly.

Annealing induced morphology evolution and phase transition in SnOx thin films grown by e-beam evaporation method

In the present work, we demonstrate the growth of tin oxide (SnOx) thin films using electron beam evaporation method to study the phase transition from stannous oxide (SnO) to stannic oxide (SnO2) by varying annealing temperature (i.e., from 300 to 700 °C). Annealing induced morphology evolution and structural modifications stimulate the process of phase-transformation, which is primarily discussed by divided the entire temperature range into two-regimes. Regime-A (from 300 to 400 °C) consists of tetragonal α-SnO dominated phase, regime-B (from 600 to 700 °C) exhibits orthorhombic pure SnO2 phase. However, these regimes are being separated by an interface conferring a mixed-phase of tin oxides at an annealing temperature ∼500 °C. This temperature-dependent phase-inversion is adequately controlled by tuning the morphological, structural and optical properties of SnOx thin films to develop homo/heterostructures for various photovoltaic and optoelectronic applications.

Understanding the Surface Structure and Catalytic Activity of SnOx/Au(111) Inverse Catalysts for CO2 and H2 Activation

Carbon dioxide hydrogenation is a promising approach for the reduction of greenhouse gas pollution via the production of fuels and high-value chemicals utilizing C1 chemistry. In this process, the activation of nonpolar molecules, CO2 and H2, at mild conditions is challenging. Herein, we report a well-defined inverse SnOx/Au(111) catalyst that shows the ability to activate both CO2 and H2 at room temperature. Scanning tunneling microscopy (STM) and ambient pressure X-ray photoemission spectroscopy (AP-XPS) are combined to understand the surface structure, growth mode, chemical state, and activity of SnOx/Au(111) surfaces. Nanostructures of SnOx at the sub-monolayer level were prepared by depositing Sn on Au(111) followed by O2 oxidation. For the as-prepared SnOx/Au(111), two-dimensionally formed SnOx thin films on a Au(111) substrate were observed with STM of two different moieties, discernible based on their height: clusters (∼0.4 Å) and nanoparticles (NPs, 1–2.5 Å), which are assigned to Sn–Au alloys and SnOx, respectively, in corroboration with XPS analysis. Furthermore, SnOx/Au(111) was annealed under UHV to test its thermal stability. Upon annealing at 400–600 K, a disappearance of SnOx NPs and reappearance of highly dispersed Sn clusters were clearly noticeable from the STM and XPS results, identifying the thermal decomposition of SnOx and subsequent formation of Sn–Au alloys on the surface due to the recombination of Sn clusters with Au. We investigated the reactivity of the SnOx/Au(111) surfaces toward CH4, CO2, and H2. The SnOx/Au(111) surfaces have excellent CO2 and H2 activation abilities even at room temperature with negligible reactivity for methane activation. Our AP-XPS results show that H2 can be activated on the SnOx NPs by the reduction to Sn. For CO2, the activation and further dissociation are identified by a reoxidation of Sn with newly formed Sn–O bonds and the formation of surface carbon. Therefore, we propose that SnOx is a potential catalyst or additive to achieve CO2 hydrogenation under mild conditions.

Optical, structural, and electrical properties of sputter-deposited SnOx thin films

This study investigated the effect of deposition parameters on the properties of tin oxide (SnOx) thin films deposited by direct current magnetron sputtering using a Sn metal target. As confirmed by optical bandgap, X-ray photoelectron spectroscopy, high-resolution X-ray diffraction and Hall effect measurements, as-grown samples deposited at 7.5 and 10% oxygen partial pressure (OPP) and post-annealed samples deposited at 5% OPP had a p-type SnO phase, whereas samples fabricated with 7.5 and 10% OPP and annealed at 400°C had a n-type SnO2 phase. Post-annealing at 400°C increases the bandgap and injects more oxygen into the SnOx thin film, further oxidizing the sample. In addition, post-annealing greatly increased the carrier concentration of the SnOx thin film, which increased carrier scattering and, in turn, greatly reduced the mobility of the sample. The SnOx thin film deposited at 7.5% OPP and not heat treated showed the best p-type properties, with a Hall mobility of 5.11 cm2/Vs, a hole carrier concentration of 1.13 × 1015 cm−3, and a resistivity of 1082 Ωcm.

Facile fabrication of defect-induced 2D-stanene/stanene-oxide nano-sheet structure material through etching of SnOx thin film by the process of successive Ar+ ion sputtering

Facile fabrication of defect-induced 2D-stanene/stanene-oxide nano-sheet structure material through etching of SnOx thin film by the process of successive Ar+ ion sputtering

Platinum-Tin/Tin Oxide/CNT Catalysts for High-Performance Electrocatalytic Ethanol Oxidation.

Ethanol is a promising liquid clean energy source in the energy conversion field. However, the self-poisoning caused by the strongly adsorbed reaction intermediates (typically, CO) is a critical problem in ethanol oxidation reaction. To address this issue, we proposed a joint use of two strategies, alloying of Pt with other metals and building Pt/metal-oxide interfaces, to achieve high-performance electrocatalytic ethanol oxidation. For this, a well-designed synthetic route combining wet impregnation with a two-step thermal treatment process was established to construct PtSn/SnOx interfaces on carbon nanotubes. Using this route, the alloying of Pt-Sn and formation of PtSn-SnOx interfaces can simultaneously be achieved, and the coverage of SnOx thin films on PtSn alloy nanoparticles can be facilely tuned by the strong interaction between Pt and SnOx . The results revealed that the partial coverage of SnOx species not only retained the active sites, but also enhanced the CO anti-poisoning ability of the catalyst. Consequently, the H-PtSn/SnOx /CNT-2 catalyst with an optimized PtSn-SnOx interface showed significantly improved performances toward the ethanol oxidation reaction (825 mA mgPt -1 ). This study provides deep insights into the structure-performance relationship of PtSn/metal oxide composite catalysts, which would be helpful for the future design and fabrication of high-performance Pt-based ethanol oxidation reaction catalysts.

Reactive thermal evaporated amorphous tin oxide fabricated at room temperature and application in perovskite solar cells

AbstractTin oxide (SnOx) as a functional layer, such as electron transport layer (ETL) or buffer layer, is widely used in perovskite solar cells (PSCs). However, SnOx prepared by spin coating is not suitable to be applied to the solar cells with large area or rough substrates. In this paper, SnOx thin films served as the ETL of PSCs were prepared using a simple reactive thermal evaporation (RTE) method, and a convenient ultraviolet ozone treatment (UV‐O3) at room temperature was carried out to replace the common post‐annealing process. The SnOx ETL prepared by RTE is suitable for substrates with arbitrary morphology, and the performance of the PSCs can be improved significantly after the ultraviolet ozone treatment of the SnOx layer. A power conversion efficiency (PCE) up to 20.62% was achieved on the planar PSCs with the RTE SnOx serving as the ETL. Conformal coverage of the RTE SnOx thin film and the perovskite layer on a textured Si surface was achieved, which is helpful for making fully textured monolithic perovskite/silicon tandem solar cells in the future.

Reaction mode-controlled crystal structure and optical and electrical properties of SnOx infrared transparent conducting films

In this study, the reaction mode of high-power pulsed reactive magnetron sputtering and the crystal structure and infrared transparent conductive properties of SnOx thin films prepared at 600 °C were investigated. The effects of sputtering at different oxygen partial pressures from 10 to 24 sccm were examined. For SnOx films deposited at oxygen partial pressures of 10–14 sccm, the reaction mode was dominated by the metallic mode, and the polar unsaturated (101) plane was the preferred orientation of the film crystals. For SnOx films deposited at oxygen partial pressures of 16–18 sccm, the reaction mode was dominated by the transition mode, showing a preferred (110) plane orientation. In the deposition process, at oxygen partial pressure >18 sccm, the reaction proceeded in poisoning mode. As the oxygen partial pressure was increased, the carrier concentration decreased to 1.140 × 1015 cm−3, mobility increased to 14.93 cm2/Vs, and IR transmittance at 4 μm increased. Furthermore, excess O2 resulted in deteriorated electrical properties of the prepared SnOx films, with a maximum resistivity of 502.9 Ω·cm.

Atomic-Layer-Deposited SiOx/SnOx Nanolaminate Structure for Moisture and Hydrogen Gas Diffusion Barriers.

High-density SnOx and SiOx thin films were deposited via atomic layer deposition (ALD) at low temperatures (100 °C) using tetrakis(dimethylamino)tin(IV) (TDMASn) and di-isopropylaminosilane (DIPAS) as precursors and hydrogen peroxide (H2O2) and O2 plasma as reactants, respectively. The thin-film encapsulation (TFE) properties of SnOx and SiOx were demonstrated with thickness dependence measurements of the water vapor transmission rate (WVTR) evaluated at 50 °C and 90% relative humidity, and different TFE performance tendencies were observed between thermal and plasma ALD SnOx. The film density, crystallinity, and pinholes formed in the SnOx film appeared to be closely related to the diffusion barrier properties of the film. Based on the above results, a nanolaminate (NL) structure consisting of SiOx and SnOx deposited using plasma-enhanced ALD was measured using WVTR (H2O molecule diffusion) at 2.43 × 10-5 g/m2 day with a 10/10 nm NL structure and time-lag gas permeation measurement (H2 gas diffusion) for applications as passivation layers in various electronic devices.

Comparison of thermal, plasma-enhanced and layer by layer Ar plasma treatment atomic layer deposition of Tin oxide thin films

In this work, Tin oxide (SnOx) thin films have been prepared by different atomic layer deposition (ALD) methods, namely thermal (T-ALD), plasma enhanced (PE-ALD) and subsequent layer by layer Ar plasma treatment (PE-ALD-ALT) modes. In the thermal plasma mode, ozone acts as the oxygen source and Tetrakis(dimethylamino)tin (TDMASn) provides the metal cation. In the plasma-enhanced mode, oxygen plasma was used as the oxygen source. For comparison, we added an Ar plasma treatment step after each layer deposition in the plasma enhanced ALD mode. Compared to T-ALD, the reaction process with O2 plasma as the oxygen source obtained higher growth per cycle (GPC) and crystallinity as well as higher carrier mobility. layer by layer Ar treatment further increased the film carrier concentration and decreased the film resistivity, which also inevitably caused a further increase in the roughness and residual stress in the film.

All-Oxide p-n Junction Thermoelectric Generator Based on SnOx and ZnO Thin Films.

Achieving thermoelectric devices with high performance based on low-cost and nontoxic materials is extremely challenging. Moreover, as we move toward an Internet-of-Things society, a miniaturized local power source such as a thermoelectric generator (TEG) is desired to power increasing numbers of wireless sensors. Therefore, in this work, an all-oxide p-n junction TEG composed of low-cost, abundant, and nontoxic materials, such as n-type ZnO and p-type SnOx thin films, deposited on borosilicate glass substrate is proposed. A type II heterojunction between SnOx and ZnO films was predicted by density functional theory (DFT) calculations and confirmed experimentally by X-ray photoelectron spectroscopy (XPS). Moreover, scanning transmission electron microscopy (STEM) combined with energy-dispersive X-ray spectroscopy (EDS) show a sharp interface between the SnOx and ZnO layers, confirming the high quality of the p-n junction even after annealing at 523 K. ZnO and SnOx thin films exhibit Seebeck coefficients (α) of ∼121 and ∼258 μV/K, respectively, at 298 K, resulting in power factors (PF) of 180 μW/m K2 (for ZnO) and 37 μW/m K2 (for SnOx). Moreover, the thermal conductivities of ZnO and SnOx films are 8.7 and 1.24 W/m K, respectively, at 298 K, with no significant changes until 575 K. The four pairs all-oxide TEG generated a maximum power output (Pout) of 1.8 nW (≈126 μW/cm2) at a temperature difference of 160 K. The output voltage (Vout) and output current (Iout) at the maximum power output of the TEG are 124 mV and 0.0146 μA, respectively. This work paves the way for achieving a high-performance TEG device based on oxide thin films.