Growth, Microstructures, and Optoelectronic Properties of Epitaxial

Subscriber access provided by - Access paid by the | UCSB Libraries

Growth, Microstructures, and Optoelectronic Properties of Epitaxial BaSn SbO Thin Films by Chemical Solution Deposition 1-x

x

3-#

Renhuai Wei, Xianwu Tang, Ling Hu, Xuan Luo, Jie Yang, Wenhai Song, Jianming Dai, Xuebin Zhu, and Yuping Sun ACS Appl. Energy Mater., Just Accepted Manuscript • DOI: 10.1021/acsaem.8b00003 • Publication Date (Web): 12 Mar 2018 Downloaded from http://pubs.acs.org on March 13, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 37 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Energy Materials

Growth, Microstructures, and Optoelectronic Properties of Epitaxial BaSn1-xSbxO3-δ Thin Films by Chemical Solution Deposition Renhuai Wei†, Xianwu Tang†, Ling Hu†, Xuan Luo*,†, Jie Yang†, Wenhai Song†, Jianming Dai†, Xuebin Zhu*,†, and Yuping Sun†,‡,§ †

Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of

Sciences, Hefei 230031, China ‡

High Magnetic Field Laboratory, Chinese Academy of Sciences, Hefei 230031, China

§

Collaborative Innovation Centre of Advanced Microstructures, Nanjing University, Nanjing

210093, China

Keywords: growth mechanism, chemical solution deposition, transparent conducting oxide, thin film, perovskite, BaSnO3

ACS Paragon Plus Environment

1

ACS Applied Energy Materials 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 37

ABSTRACT Epitaxial thin films of perovskite BaSn1-xSbxO3-δ are fabricated by a simple chemical solution deposition method, and the relationship among the processing, the microstructure and the optoelectronic property are systematically investigated. The process of multiple annealing combined with the post annealing under nitrogen ambient is the optimal procedure to fabricate high quality BaSnO3-δ thin films. Sb doping in Sn sites facilitates the epitaxial growth of the BaSnO3-δ grains. The Hall results display that with increasing Sb doping content the carrier density and the carrier mobility is enhanced and decreased, respectively, resulting in the highest room temperature electrical conductivity of 260 S/cm in the BaSn0.91Sb0.09O3-δ thin film. It is confirmed that the ionized Sb5+ and oxygen vacancies are the main scattering sources for carrier transport in BaSn1-xSbxO3-δ thin films. The results will provide guidance for synthesis of BaSnO3δ-based

and other donor-doped perovskite transparent conducting large-area thin films with low

cost.


2

Page 3 of 37 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1. INTRODUCTION Recent developments in information and energy technologies stimulates the extensive exploration of transparent conducting oxides (TCOs), which combine two contradictory features, visible light transparency and electrical conductivity, in a singular object. TCOs are utilized widely in the window layers of solar cells, as front electrodes in flat panel displays, organic/polymer light emitting diodes, antistatic coatings, invisible security circuits, and so on.1-6 Most of the TCOs are donor-doped metal oxides, such as Sn-doped In2O3 (ITO), ZnO, and SnO2.7,8 However, these materials were confronted some limitations, such as ingredient scarcity and degradation.9 Therefore, alternative transparent and conducting materials are needed to be discovered, for fulfilling the huge demands in optoelectronic applications. Perovskite TCOs have significant potential for electronic, photovoltaic and solar energy conversion devices due to their multiplicity of advantageous physical properties.10-12 Currently, perovskite TCOs including BaSnO3-, SrTiO3-, SrGeO3-, LaCrO3-, and Ca/SrVO3-based thin films have been investigated widely.1,13-17 Amongst these TCOs, BaSnO3-based thin films are investigated intensively due to the wide bandgap (~3.2 eV) and excellent room temperature conductivity as well as high electronic mobility and good thermal stability.18-20 In particular, Shin et al. reported that the power conversion efficiency for fully solidified perovskite solar cells (methylammonium lead iodide (MAPbI3) as a light harvester) can be improved from 19.7% to 21.2% by replacing mesoporous TiO2 (n-type electron-transporting layer) with perovskite Ladoped BaSnO3.21 Meanwhile, the stability of solar cells could retain 93% of their initial performance after long time of full-Sun illumination.21 In BaSnO3, Sn4+ occupies 6-fold coordination and Ba2+ is accommodated in center of 12coordinate cavity, showing an ideal perovskite structure.22 BaSnO3 is hard to be used as a n-type


3


Page 4 of 37

electron-transport layer for solar cells since its insulating property of undoped one. To obtain conductivity, doping heterovalent elements into Ba or Sn sites have been carried out.13,18-20,23-26 Although high conductivity was achieved through doping Ba by La element,13,20 the optoelectronic performance shows quite different even the processing parameters are similar,19,20,23-25 which are needed to carry out systematic investigations to clarify the growth mechanisms as well as physical explanation. On the other hand, Sb doping at Sn sites is another route to get high conductivity in BaSnO3 system.27-30 Cava et al. reported that the room temperature electrical conductivity increases with several orders of magnitude from the undoped BaSnO3-δ (BSO) ceramic (~0.01 S/cm) to BaSn0.85Sb0.15O3-δ one (~50 S/cm).27 Subsequently, the high room temperature conductivity with the value of ~10 S/cm is obtained for the BaSn0.93Sb0.07O3-δ ceramics as studied by Huang et al.28 Mizoguchi et al. found that the optimized room temperature electrical conductivity (less than 10 S/cm) for the BSO ceramics is saturated when the Sb doping content increases to 10% in Sn sites.29 Moreover, Kim et al. observed that the electrical conductivity is less dependent on Sb dopant content for the BaSn1xSbxO3

single crystals.30 The large frustration in electrical transport properties for the Sb-doped

BSO bulks demonstrates that the electron conduction mechanisms are controversial. Furthermore, for the fabrication of perovskite n-type electron-transporting layers (to enhance the stability of solar cells) applied to fully solidified perovskite solar cells,21 high quality, superior properties and epitaxial Sb-doped BSO thin films rather than bulks are desired. However, the reports on Sb-doped BSO thin films are few,23,31 and the discrepancy in optoelectrical properties are still existent. The lack of unified explanation for the determination of optoelectronic properties motivates us to explore the relationship among the processing, microstructures as well as physical properties for the Sb-doped BSO thin films in detail.


4

Page 5 of 37 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Currently, BSO-based thin films have been frequently fabricated by physical methods, such as pulsed laser deposition (PLD) and molecular beam deposition (MBE) up to date.13,19,20,23-25,30,31 Thin film fabrication with the advantages of high-speed, miniaturization and low cost is very important from the viewpoint of basic science and application in devices, especially for heteroepitaxial structures. Chemical solution deposition (CSD) is an effective route to prepare heteroepitaxial structures with low cost, ability to fabricate stoichiometric large-area thin films with atomic mixing.32,33 Previously, we reported that high-performance La-doped BaSnO3 thin films can be successfully prepared by the CSD, and the electronic mobility can be obviously enhanced by introduction of oxygen vacancies.26 Here, we report successful growth of BSO and Sb-doped BSO thin films by the CSD method. Detailed thin film growth, microstructures, optical and electrical properties, and carrier scattering mechanisms are systematically investigated. 2. EXPERIMENTAL METHODS The sketch for preparing processes is illustrated in Figure 1a. Precursor solutions with a concentration of 0.2 M for the deposition of thin films were prepared by the usage of stoichiometric barium acetate (Ba(CH3COO)2), lanthanum acetate sesquihydrate (La(CH3COO)3•3/2H2O), stannic chloride pentahydrate (SnCl4•5H2O) and antimony acetate (Sb(CH3COOH)3) as the starting solutes. The mixture solution of ethylene glycol (EG) and glacial acetic acid (GAA) (the volume ratio is 3:2) was used as solvent. The starting solutes were dissolved into the solvent at 70 °C for 20 minutes by the usage of a magnetic stirring with ultrasonic assistance. The obtained clear solutions were stirred further for 10 h at room temperature. After aging for 24 h, the coating solutions were deposited onto commercial (100)-oriented STO single crystal substrates by a spin-coater. The used substrates were cleaned by ultrasonic-


5


Page 6 of 37

baths in acetone, ethanol and deionized water in sequence, followed by a final cleaning using a plasma cleaner. The processing of spin-coating was performed at a rotation speed of 7000 rpm for 10 s with the ambient temperature over 50 °C. Here, different preparing processes including the single annealing (SA), the multiple annealing (MA) and further the post annealing (PA) were performed to fabricate BaSnO3-δ and BaSn1-xSbxO3-δ (x=0.03, 0.06, 0.09, 0.12, 0.15, 0.20) thin films.

Figure 1. (a) A sketch of the preparation of BaSnO3-δ thin films by chemical solution deposition. (b)-(d) Three selected XRD patterns (left), rocking curves (middle) and φ-scanning


6

Page 7 of 37 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


results (right) of BaSnO3-δ thin films with identical coatings synthesized by different annealing processes. (e) A schematic diagram for epitaxial relationship between the BaSnO3-δ thin film and the SrTiO3 substrate. (f) Cross-sectional TEM image near the thin film-substrate interface for the BaSnO3-δ thin film prepared by the MA&PA process. (g) Selected-area electron diffraction pattern for the MA&PA-processed BaSnO3-δ thin film combined with the SrTiO3 substrate, in which different crystallographic planes are marked. Mono-chromatic X-ray diffraction (XRD, PANalytical) analysis with Cu-Kα radiation was used to identify the thin film phase purity and characterize the orientation as well as epitaxy. Field-emission scanning electron microscopy (FE-SEM, Hitachi-designed, SU8020) was used to check up the surface morphologies and the cross-sectional thickness. Transmission electron microscopy (TEM, JEM-2010) was utilized to determine the interface between thin film and the substrate. The ionic valences for all thin films were recorded by an X-ray photoelectron spectroscopy (XPS, Thermo ESCALAB 250) using an anticathode of Al-Kα (1486.6 eV) in an ultrahigh vacuum chamber. The binding energy data were referenced to the C 1s peak at 284.8 eV. Electrical conductivity was measured using the standard four-probe method on a Quantum Design Physical Properties Measurement System (PPMS-9T). Room-temperature Hall effect measurements were also carried out on the PPMS in a magnetic field up to 5 T. Optical transmission measurements were performed using an UV/Vis/NIR spectrometer (VARIAN, CARY-5E). 3. RESULTS AND DISCUSSION The BSO thin films were prepared by the CSD method with different annealing ways including the single annealing (SA), the multiple annealing (MA) and the post annealing (PA) processes (as shown in Figure 1a), in order to explore the superior procedure for preparing high


7


Page 8 of 37

quality BSO thin films. The process of SA refers the spin-coating and baking (400 °C) procedures were repeated for six times, and then annealed at 800 °C. As for the MA process, the procedures of spin-coating, baking and annealing (800 °C) were repeated for six times. To further improve the crystalline quality, the process of PA (at 1000 °C) was also performed. In addition, the MA&PA (SA&PA) process refers the BSO thin film with PA process under nitrogen or air atmosphere after the process of MA (SA). It should be noted here that all annealing processes are rapid thermal annealing (RTA), in which the as-prepared thin films were directly inserted into the silica tube preheated to the designed temperature. The X-ray diffraction (XRD) results of three typical BSO thin films prepared by different processes are presented in the left of Figure 1b to 1d, in which one can see that the thin films are pure BSO phase (JCPDS No. 15-0780) with (100) orientations. According to the Bragg formula, 2dsinθ=nλ (where d, θ, and λ is the lattice constant, diffraction angle and X-ray wavelength, respectively), the lattice constant is 4.109 Å, 4.112 Å, and 4.115 Å for the BSO thin films prepared by the SA, the MA and the MA&PA process, respectively. The enhancement in lattice constant should be related with the increasing oxygen vacancy VO. For the SA-processed BSO thin film, the baked thin film is annealed at 800 °C in air and the crystallization is realized within the whole thickness (~100 nm). As for the BSO thin film fabricated by the MA process, the annealing procedure is carried out for each coating (~20 nm), resulting in the enhanced oxygen vacancies due to the air atmosphere as well as the high annealing temperature. With further increasing the PA process temperature to 1000 °C, the oxygen vacancies will be further enhanced due to the enhanced oxygen diffusion. The results of rocking and φ-scanning measurements for the three BSO thin films are shown in the middle and the right of Figure 1b to 1d, respectively, which give a comparison of out-of-


8

Page 9 of 37 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


plane and in-plane orientations for the BSO films synthesized by different processes. For rocking measurements on (200) diffraction peaks, it is seen that the BSO thin film prepared by the MA process shows a smaller full-width at half-maximum (FWHM) value of 0.79° than that of the thin film fabricated by the SA process (1.21°), suggesting the MA process is more favorable for out-of-plane orientation. Moreover, the thin film of BSO synthesized with further PA process after MA displays a further reduction in FWHM value to 0.52° for rocking curve, indicating that the MA&PA-processed BSO thin films present well-defined out-of-plane orientated character. Moreover, in order to check up the epitaxy for the prepared BSO thin films, X-ray φ-scans are performed on (110) reflections for both BSO thin films and SrTiO3 (STO) (100) substrates. A set of four distinct peaks with 90° separation can be clearly seen for each thin film, suggesting that the BSO thin films deposited on the STO (100) substrates have an epitaxial relationship of BSO(100)[110]||STO(100)[110] (see Figure 1e). According to the φ-scanning patterns, the average FWHM values are 2.01°, 1.37°, and 0.89° for the thin films prepared by the SA, the MA and the MA&PA process, respectively. Such decreasing trend clearly indicates that the epitaxy of the BSO thin film can be much improved by MA process as well as PA treatment. Additionally, the microstructures of the BSO thin film prepared by MA&PA process are investigated by the cross-sectional transmission electron microscopy (TEM) as shown in Figure 1f. It is observed that the BSO thin film grows epitaxially on STO substrate with cube-on-cube growth mode, in good agreement with the X-ray φ-scanning results. Also, the selected-area electron diffraction pattern (as present in Figure 1g) obtained for the BSO thin film combined with the STO substrate confirms the epitaxial relationship. The divided electron diffraction spots of (100)-plane and (110)-plane (as marked in Figure 1 g) between the thin film and the substrate can be elucidated by the large lattice mismatch ((as-af)/af=-5.6%, where as and af refer to the


9


Page 10 of 37

lattice constant for the substrate and the thin film, respectively) for the BSO thin film and the STO substrate. The surface morphologies of the derived BSO thin films with different preparing processes and coatings are shown in Figure 2a to 2f. It is seen that all thin films display relatively dense surfaces with different grain sizes. For the BSO thin film prepared by the SA process (Figure 2a), the grain size is less than 20 nm. With further PA process for the as-SA-prepared BSO thin film, the grain size is enhanced as shown in Figure 2b. For the BSO thin films fabricated by the MA process, a dense surface is obtained for the BSO thin film with a single coating (Figure 2c). With increasing the coatings, the grain size is obviously enhanced. Additionally, as compared with the BSO thin film by SA process with the same coatings (Figure 2a), the thin film deposited by the MA process shows a larger grain size (Figure 2e). Similar to that of the SA-processed BSO thin film, as shown in Figure 2f, the process of PA can also obviously enhance the grain size for the BSO thin films prepared by the MA process. It should be pointed out here that the larger grain size will lead to the depressed carrier scattering due to the decrease in grain boundaries, which is favorable for the improvement in carrier mobility.


10

Page 11 of 37 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 2. (a)-(f) FE-SEM images for crystallized BaSnO3-δ thin films fabricated by the SA, the MA as well as the MA&PA processes. (g) and (h) The detailed schematic diagrams of the BaSnO3-δ thin film fabrication processes including the SA, MA and further the PA, where the (g) denotes the SA and further PA process while the (h) gives the MA and further the PA process. As mentioned above, the prepared BSO thin films epitaxially grow on STO substrates whatever the process is used, although different morphologies are observed. Firstly, as for the enhancement in grain size due to PA process both for the SA or MA-prepared BSO thin film, the cation diffusion will increase with increasing annealing temperature as well as the prolonging dwell time, resulting in the enhanced diffusion distance and the grain size. As for the differences in surface morphologies for the SA and MA-prepared BSO thin films with different coatings, Figure 2g and 2h present the schematic diagrams of the BSO thin film fabrication processes, respectively. For the BSO thin film by the SA process as shown in Figure 2g, the baked thin films with 1 coating or 6 coatings are amorphous (confirmed by XRD and not shown here). During the baking procedure, the evaporation of water, solvent and organic ligand is the dominant reaction. Subsequently, the baked thin films are annealed at a high temperature, which will lead to the crystallization of the amorphous thin film. During this procedure, the nucleation may occur at different locations (substrate interface, surface, and inside the amorphous phase). However, according to the theory of crystallization, the nucleation is delayed resulting in the lower driving force in RTA processing,32 which is favorable for heterogeneous nucleation. Therefore, nucleation at the thin film-substrate interface is preferred, leading to the (100) epitaxy for the derived BSO thin films. On the other hand, due to the large lattice mismatch (-5.6%) between the BSO and the STO, the grain size is relatively small as shown in Figure 2a. With further PA process, the BSO grain size is increased due to the enhanced thermal budget. Figure


11


Page 12 of 37

2h displays the procedures for the fabrication of BSO thin films by the MA process. For the thin film with one coating, the grain growth is similar to that prepared by the SA process. While for the BSO thin films with enhanced coatings in the MA process, the amorphous phase will crystallize onto the crystallized BSO grains, which can be regarded as the seeds. The nucleation will occur onto these seeds with low interfacial energy,32 resulting in the enhanced epitaxy as well as larger grain size due to the absence of lattice mismatch. Based on these results, it can conclude that the MA&PA process is the optimal route to fabricate BSO thin films with enhanced morphologies by the CSD method. However, the obtained BSO thin films show insulating behavior, and the conductivity is too low to be measured by the standard four-probe method. Therefore, the BSO thin films with Sb doping at Sn sites are carried out to enhance the conductivity. Phase-pure BaSn1-xSbxO3-δ (0.03≤x≤0.20) thin films are confirmed by the XRD measurements, and the (200) diffraction peak shifts to the lower diffraction angle when the Sb content is increasing according to the magnified (200) peaks in XRD patterns (Figure 3a), suggesting the increment of the lattice constant. The calculated lattice constant versus Sb doping content is shown in Figure 3(b). It is seen that the lattice constant initially increases with the increasing Sb content, but the lattice constant tends to saturate when the Sb content is higher than 0.12, which is same as the previous reports about Sb-doped BSO bulks.27-30 For the viewpoint of the ionic radius, it is deduced that the Sn4+ (0.69 Å) ion is substituted by Sb3+ (0.72 Å) one, which will lead to the increment of the lattice constant. However, the Hall measurements show that the Sbdoped BSO system present donor-doped type, which is suggestive of Sb5+. The valence state of +5 for the dopant Sb is also confirmed by X-ray photoelectron spectroscopy (XPS) measurement as discussed later. Firstly, according to the first-principle calculations, the lattice expansion in


12

Page 13 of 37 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


response to Sb doping can be explained by the repulsive forces between Sn and O to lower the total energy of the crystal structure, which is deduced by the antibonding character of the electronic states.30 On the other hand, the formation of oxygen vacancy (loss of oxygen) may occurs when Sn4+ was replaced by Sb5+ (shown later) in order to balance the charge valence. The absence of oxygen may result in an increment of electrostatic repulsion between the cations, and therefore an expansion of the lattice, which was also found in perovskite SrTiO3 systems.34 For the Sb-doped BSO thin film with x≥0.12, however, the saturation of lattice constant is due to the solid solubility limit occurs at x=0.12, which was also observed in the polycrystalline bulks.27-30

Figure 3. (a) Magnified (200) diffraction peaks for all Sb-doped BaSnO3-δ thin films. (b) Evolution of lattice constant, FWHM value of rocking curve for (200) peak, and average FWHM value of φ-scanning in response to Sb doping content for all derived thin films. (c)-(h) FE-SEM images for BaSn1-xSbxO3-δ (x=0.03, 0.06, 0.09, 0.12, 0.15, and 0.20) thin films. In addition, the out-of-plane as well as in-plane orientation for all Sb-doped BSO thin films are checked out by the rocking and X-ray φ-scanning measurement, and the evolution of FWHM value in response to Sb content is shown in Figure 3b. It is seen that the FWHM value of the rocking curve decreases with increasing Sb doping content, indicating the improvement of out-


13


Page 14 of 37

of-plane orientation. As for the in-plane orientation, the average FWHM value of the φ-scanning is also decreased with Sb doping, indicating the enhancement of in-plane orientation by Sb doping. It is speculated that the crystallization temperature of the BSO phase is decreased with Sb doping, which will result in the enhanced grain growth in both out-of- and in-plane orientations. Actually, such evolution of grain growth in response to Sb content has been observed in the Sb-doped BSO single crystals.30 Figure 3c to 3h give the surface morphologies for all Sb-doped BSO thin films. It is interesting to observe that the derived Sb-doped BSO thin films are composed of stacked cubic grains and the grain boundary can be clearly seen, indicating the high crystallinity. Moreover, all the BSO grains arrange along the unique direction, suggesting the epitaxial growth of the BSO grains on STO substrates as also checked by the X-ray φ-scanning. Figure 4 plots the optical transmittance spectra for the Sb-doped BSO thin films, and the transmittance result for the undoped BSO thin film is also given for comparison. It is shown that the dopant Sb has much influence on optical transmittance. In the ultraviolet spectral region, the transmittance decreases sharply to zero with increasing photon energy, which is related to the intrinsic characteristic of light absorption for STO substrate. In the visible region, all thin films show the optical transmittance with the range of 50-75% (including the substrates), in which the average transmittance for Sb-doped BSO thin films on STO substrates, as calculated by the averaging values at photon energies of 1.77, 2, 2.25, 2.5, and 2.75 eV, is shown in the inset of Figure 4. It is seen that all Sb-doped BSO thin films show high average optical transmittance with the values over 60%, which is much higher than that of the previous report on PLD-derived thin films.31 According to the relation, T≈exp[-α(λ)d], where the parameters T, α(λ), and d are the transmittance, wavelength related absorption coefficient and thin film thickness,


14

Page 15 of 37 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


respectively,16 thin films with the lower thickness have a higher optical transmittance at the fixed wavelength and doping content. Here, the CSD-derived BSO thin films have the thickness of 100 nm, which is much thinner than that of the PLD-derived thin films (600 nm),31 and thereby possess higher optical transmittance. In addition, the average transmittance decreases continuously with increasing Sb doping content, which can be elucidated by the increasing carrier density related free carrier absorption.35 Moreover, within the infrared region, the transmittance for all Sb-doped BSO thin films is suppressed with decreasing the photon energy, resulting in the Drude-type absorption tails due to the increase of free carriers.30

Figure 4. Optical transmittance results for all Sb-doped BaSnO3-δ thin films. The inset shows the calculated average optical transmittance in the visible region. To reveal the Sb doping effect on electrical transport properties for the derived thin films, the temperature dependence of electrical conductivity is measured, and the results are shown in Figure 5. Here, to give a clear comparison on processing effects on conductivity, the electrical conductivity for the thin films of Sb-doped BSO (x=0.09) with the processes of MA (0.09/MA) and MA&PA under air (0.09/MA&PA/air) are also given. It is seen that the electrical


15


Page 16 of 37

conductivity is highly dependent on the Sb doping content as well as the processing parameters. For the Sb-doped BSO thin films prepared by MA&PA process under nitrogen atmosphere (x/MA&PA/N2), the conductivity shows a similar temperature dependent behavior, which initially increases with increasing measurement temperature in the low temperature ranges, and then the conductivity saturates gradually with further increasing the temperature in the elevated temperature regions. The low electrical conductivity in lower temperatures is related to the localization of carriers.30 With increasing the measurement temperature, more electrons are thermally activated, resulting in the enhancement of electrical conductivity. Moreover, it can be seen from Figure 5 that the conductivity for the thin films of 0.09/MA and 0.09/MA&PA/air are much lower than that of the thin film 0.09/MA&PA/N2, indicating that the MA&PA process is more favorable than that of other procedures.

Figure 5. Temperature dependent electrical conductivity of BaSn1-xSbxO3-δ (x=0.03, 0.06, 0.09, 0.12, 0.15, and 0.20) thin films prepared by different processes. The room-temperature electrical conductivity (extracted from the Figure 5) for the BSO thin films prepared by different doping contents and processing parameters is shown in Figure 6a. Firstly, for the Sb-doped BSO thin films prepared with MA&PA process under nitrogen


16

Page 17 of 37 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


atmosphere, it is clearly seen that the conductivity initially increases with increasing Sb content from 0.03 to 0.09 and then decreases with further increasing Sb doping content. The maximum value of 260 S/cm is obtained for the BaSn0.91Sb0.09O3-δ thin film, which is much higher than that of the polycrystalline bulks.27-29 On the other hand, the thin films of BaSn0.91Sb0.09O3-δ fabricated by the MA and MA&PA processes with air annealing show inferior room-temperature conductivity, which is related to the inferior crystalline quality.

Figure 6. Evolution of room temperature (T=300K) electrical conductivity with respect to Sb doping content (a), Hall results (b), Sb content dependence of room temperature carrier density (c) and mobility (d) for all BaSn1-xSbxO3-δ (x=0.03, 0.06, 0.09, 0.12, 0.15, and 0.20) thin films.


17


Page 18 of 37

To get an insight of the electrical transport properties for the Sb-doped BSO thin films, Hall measurements are carried out, and the results of Hall resistance versus the applied magnetic field are plotted in Figure 6b. The negative slops indicate the donor-doped BSO thin films are obtained. According to the formula, RH=B/ned (RH the Hall resistance, B the magnetic field, n the carrier density, e the electron charge, and d the film thickness along the direction of B), the room-temperature carrier density is calculated, and the results are shown in Figure 6c. For the Sb-doped BSO thin film by the MA&PA/N2 process, it is obviously seen that the carrier density initially increases with a sharp slop from x=0.03 to x=0.12, and then saturates with further increasing the Sb doping content. Such trend is analogous to that of the lattice constant (Figure 3b), suggesting the dopant limit is about 0.12. If each Sb5+ dopant provide one free electron, the expected carrier density in the Sb-doped thin films should be 4.29×1020, 8.58×1020, 12.84×1020, 17.08×1020, 21.34×1020, and 28.45×1020 cm-3 for the x=0.03, 0.06, 0.09, 0.12, 0.15, and 0.20 thin films, respectively. In fact, the measured carrier density values are lower than the expected results. Assuming 1 electron/Sb, then the dopant activation rate is calculated as 46%, 53%, 47%, 44%, 35%, and 27% for samples x=0.03, 0.06, 0.09, 0.12, 0.15, and 0.20, respectively. Such observation indicates that more than half of the expected free carriers are likely to be trapped or localized. In addition, it can be also seen from Figure 6c that the Sb-doped BSO thin films prepared by the processes of MA and MA&PA/air show lower carrier density as compared with that of the thin film by the MA&PA/N2 process, which can be attributed to the lower oxygen vacancies as discussed below. Moreover, the Sb doping content dependent carrier mobility µ at 300 K calculated from σ=eµn (σ refers the conductivity) is shown in Figure 6d. It is seen that the highest carrier mobility with the magnitude of 3.3 cm2/Vs is obtained for the BaSn0.97Sb0.03O3-δ thin film. Such value is close to the previous results about Sb-doped BSO thin films by PLD31


18

Page 19 of 37 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


but much smaller than that of the La-doped BSO thin films by CSD26 as we reported earlier. As compared with the thin films of La-doped BSO (La for Ba sites), the substitute of Sb for Sn will lead to more scattering centers since the main conduction paths in BSO is related to the SnO6 octahedral networks.19 In addition, as shown in Figure 6d, the mobility decreases progressively with increasing Sb doping content, which is attributed to the enhanced ionized impurities such as Sb5+ and oxygen vacancy VO. To further confirm the substitution of Sn by Sb in the prepared BSO thin films, XPS measurements of Ba, Sn, Sb and O elements are performed for the selected Sb-doped BSO (x=0.00, 0.03, 0.09, and 0.15) thin films and the results are shown in Figure 7. In comparison, the XPS results for the thin films of 0.09/MA and 0.09/MA&PA/air are also given. As seen from Figure 7a, no obvious position change of the spin-orbit splitting reduced Ba 3d3/2 and Ba 3d5/2 located at 795.1 and 779.7 eV, respectively, is observed. Thus, Ba2+ state within Ba-O bonds are the same in all Sb-doped BSO thin films. Figure 7b shows the fitted Sn 3d XPS spectra of the Sb-doped BSO thin films with different doping contents and processes. Here, similar to the study on ZnSnO3 thin films,36 the Sn 3d peaks for Sb-doped BSO thin films are decomposed into three components, of which appear at 485.6±0.3 eV for the Sn with low valence (Sn2+), 486.3±0.3 eV for the Sn4+ in BSO crystal lattice, and 487.2±0.3 eV for the Sn4+ adjacent to oxygen vacancy. The evolution of the relative concentrations for the above three components with Sb doping content is presented in Figure 7d to 7f. With increasing the Sb doping content, the concentration of Sn2+ increases while the Sn4+ decreases to meet the charge balance law. Meanwhile, the concentration of Sn4+ adjacent to oxygen vacancy increases with increasing Sb content, implying the enhanced oxygen vacancies with Sb doping.


19


Page 20 of 37

Figure 7. XPS of BaSn1-xSbxO3-δ thin films within Ba 3d region (a), Sn 3d region (b), Sb 3d and O 1s regions (c). (d)-(h) Evolution of Sn2+, Sn4+ in crystal lattice, Sn4+ adjacent to oxygen vacancy, oxygen adjacent to Sn2+ (O-Sn), and oxygen vacancy in response to Sb doping content, which are deduced by the fitting results of XPS spectra as shown in (b) and (c). Figure 7c shows the XPS spectra of Sb 3d and O 1s for the Sb-doped BSO thin films. The peak at 540.1 eV binding energy is ascribed to Sb 3d3/2 level,31 while the Sb 3d5/2 and O 1s levels are overlapped at lower binding energies. It is also found that there is no obvious chemical shift with different Sb doping contents and fabrication processes. These results imply that the valence state of dopant Sb is close to the single +5 state without the +3 state.31 Thus, the dopant of Sb5+ for Sn4+/Sn2+ offers electron carriers, which is in good agreement with the Hall measurements. The changes in oxygen vacancy VO for different Sb doping contents can be derived by the decomposition of O 1s spectra. As shown in the range of low binding energies, the Sb 3d5/2 and O 1s spectra are decomposed into five components, of which the peak at 529.2±0.3 eV is the


20

Page 21 of 37 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


oxygen adjacent to low valence Sn2+ (O-Sn),36 at 529.9±0.3 eV for the lattice oxygen (Ba-OSn),36 at 530.75 eV for Sb 3d5/2,31 at 531.3±0.3 eV for the VO,36,37 and at 532.2±0.3 eV for the oxygen in hydroxyl group (OH-)36,37. Based on the fitting results, the Sb doping content dependence of the relative concentrations for the oxygen adjacent to Sn2+ (O-Sn) and oxygen vacancy (VO) are given in Figure 7g and 7h, respectively. It is shown that the concentration of the oxygen adjacent to Sn2+ increases with increasing Sb doping content, consistently with the changes in decomposed Sn2+ concentration (Figure 7d). In addition, the oxygen vacancy increases with increasing Sb doping content. Based on these results, the decrease in carrier mobility with Sb doping content can be reasonably explained by the enhanced carrier scattering due to the increased ionized Sb5+ and oxygen vacancy VO impurities. Additionally, as seen in Figure 7h, thin film of 0.09/MA has a lower concentration of oxygen vacancy than that of the 0.09/MA&PA/air thin film, and both two thin films have a lower content of vacancy than that of the thin film 0.09/MA&PA/N2, which will lead to the decreased carrier densities. 4. CONCLUSIONS In summary, epitaxial BaSnO3-δ and Sb-doped BaSnO3-δ thin films were successfully fabricated on SrTiO3 (100) substrates by a chemical solution deposition route. Firstly, the effects of different processing procedures including the single annealing, multiple annealing, and further post annealing on the microstructures were performed. As compared with the process of single annealing, it is found that thin films of BaSnO3-δ with dense surface and large grain size were derived by the multiple annealing process due to the homogeneous epitaxial growth of BaSnO3-δ thin film on the as-crystallized BaSnO3-δ seeds. With further post annealing process for the multiple annealed thin film, the crystalline quality is further increased. On the other hand, the effects of Sb doping in Sn sites with the doping range of 0.03≤x≤0.20 on the microstructures as


21


Page 22 of 37

well as optoelectronic properties for the BaSnO3-δ thin films were investigated. It was observed that all phase-pure Sb-doped BaSnO3-δ thin films exhibit increasing lattice constant in response to the Sb doping content, which can be interpreted by the antibonding character of the electronic states deduced repulsive forces between Sn and O as well as the absence of oxygen produced electrostatic repulsion between the cations. Moreover, the in-plane and out-of-plane orientation for BaSn1-xSbxO3-δ thin films increased with increasing of Sb content, which were proved by the rocking curves, X-ray φ-scanning as well as surface morphologies characterization. According to the results of optical transmittance, it is found that the average visible transmittance decreased with increasing Sb dopant content and maintains at a value over 60% (including the SrTiO3 substrates) even for heavily doped thin films. Furthermore, the highest electrical conductivity with the value of 260 S/cm was obtained for Sb content of 9% in Sn sites. Hall results demonstrated that the carrier mobility for Sb-doped BaSnO3-δ thin films decreased progressively with increasing carrier density, which can be mainly explained by the increasing ionized Sb5+ and VO impurities scattering on carriers. Finally, as compared with the process of multiple annealing and multiple annealing & post annealing under air ambient, thin films of Sb-doped BSO prepared by the process of multiple annealing & post annealing under nitrogen atmosphere present higher carrier density and mobility. AUTHOR INFORMATION Corresponding Author *,†

E-mail: [email protected].

*,†

E-mail: [email protected].

The authors declare no competing financial interest.


22

Page 23 of 37 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


ACKNOWLEDGMENT This work was financed by the National Natural Science Foundation of China under contract No. 11604337, the Nature Science Foundation of Anhui Province under contract 1508085ME103 and the Director’s Fund of Hefei Institutes of Physical Science under contract No. YZJJ201513.


23


Page 24 of 37

REFERENCES 1. Lee, W.; Kim, H. J.; Kang, J.; Jang, D. H.; Kim, T. H.; Lee, J. H.; Kim, K. H. Transparent Perovskite Barium Stannate with High Electron Mobility and Thermal Stability. Annu. Rev. Mater. Res. 2017, 47, 391–423. 2. Fortunato, E.; Barquinha, P.; Martins, R. Oxide Semiconductor Thin-Film Transistors: A Review of Recent Advances. Adv. Mater. 2012, 24, 2945–2986. 3. Fortunato, E. M. C.; Barquinha, P. M. C.; Pimentel, A. C. M. B. G.; Gonçalves, A. M. F.; Marques, A. J. S.; Pereira, L. M. N.; Martins, R. F. P. Fully Transparent ZnO Thin-Film Transistor Produced at Room Temperature. Adv. Mater. 2005, 17, 590–594. 4. Nomura, K.; Ohta, H.; Takagi, A.; Kamiya, T.; Hirano, M.; Hosono, H. Room-Temperature Fabrication of Transparent Flexible Thin-Film Transistors using Amorphous Oxide Semiconductors. Nature 2004, 432, 488–492. 5. Hoffman, R. L.; Norris, B. J.; Wager, J. F. ZnO-Based Transparent Thin-Film Transistors. Appl. Phys. Lett. 2003, 82, 733–735. 6. Carcia, P. F.; McLean, R. S.; Reilly, M. H.; Nunes, G. Transparent ZnO Thin-Film Transistor Fabricated by rf Magnetron Sputtering. Appl. Phys. Lett. 2003, 82, 1117–1119. 7. Lee, S.-H.; Han, S.-H.; Jung, H. S.; Shin, H.; Lee, J.; Noh, J.-H.; Lee, S.; Cho, I.-S.; Lee, J.K.; Kim, J.; Shin, H. Al-Doped ZnO Thin Film: A New Transparent Conducting Layer for ZnO Nanowire-Based Dye-Sensitized Solar Cells. J. Phys. Chem. C 2010, 114, 7185–7189. 8. Wang, Z.; Nayak, P. K.; Caraveo-Frescas, J. A.; Alshareef, H. N. Recent Developments in pType Oxide Semiconductor Materials and Devices. Adv. Mater. 2016, 28, 3831–3892. 9. Ellmer, K. Past Achievements and Future Challenges in the Development of Optically Transparent Electrodes. Nat. Photonics 2012, 6, 809–817.


24

Page 25 of 37 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


10. Ahn, C. H.; Triscone, J.-M.; Mannhart, J. Electric Field Effect in Correlated Oxide Systems. Nature 2003, 424, 1015–1018. 11. Auciello, O.; Scott, J. F.; Ramesh, R. The Physics of Ferroelectric Memories. Phys. Today 1998, 51, 22–27. 12. Mbenkum, B. N.; Ashkenov, N.; Schubert, M.; Lorenz, M.; Hochmuth, H.; Michel, D.; Grundmann, M.; Wagner, G. Temperature-Dependent Dielectric and Electro-Optic Properties of a ZnO-BaTiO3-ZnO Heterostructure Grown by Pulsed-Laser Deposition. Appl. Phys. Lett. 2005, 86, 091904. 13. Prakash, A.; Xu, P.; Faghaninia, A.; Shukla, S.; Ager III, J. W.; Lo, C. S.; Jalan, B. Wide Bandgap BaSnO3 Films with Room Temperature Conductivity Exceeding 104 S cm-1. Nature Commun. 2017, 8, 15167. 14. Son, J.; Moetakef, P.; Jalan, B.; Bierwagen, O.; Wright, N. J.; Engel-Herbert, R.; Stemmer, S. Epitaxial SrTiO3 Films with Electron Mobilities Exceeding 30,000 cm2 V−1 s−1. Nature Mater. 2010, 9, 482–484. 15. Mizoguchi, H.; Kamiya, T.; Matsuishi. S.; Hosono, H. A Germanate Transparent Conductive Oxide. Nature Commun. 2011, 2, 470. 16. Zhang, K. H. L.; Du, Y.; Papadogianni, A.; Bierwagen, O.; Sallis, S.; Piper, L. F. J.; Bowden, M. E.; Shutthanandan, V.; Sushko, P. V.; Chambers, S. A. Perovskite Sr-Doped LaCrO3 as a New p-Type Transparent Conducting Oxide. Adv. Mater. 2015, 27, 5191–5195. 17. Zhang, L.; Zhou, Y.; Guo, L.; Zhao, W.; Barnes, A.; Zhang, H.-T.; Eaton, C.; Zheng, Y.; Brahlek, M.; Haneef, H. F.; Podraza, N. J.; Chan, M. H. W.; Gopalan, V.; Rabe, K. M.; EngelHerbert, R. Correlated Metals as Transparent Conductors. Nature Mater. 2016, 204–210.


25


Page 26 of 37

18. Luo, X.; Oh, Y. S.; Sirenko, A.; Gao, P.; Tyson, T. A.; Char, K.; Cheong, S.-W. High Carrier Mobility in Transparent Ba1-xLaxSnO3 Crystals with a Wide Band Gap. Appl. Phys. Lett. 2012, 100, 172112. 19. Kim, H. J.; Kim, U.; Kim, H. M.; Kim, T. H.; Mun, H. S.; Jeon, B.-G.; Hong, K. T.; Lee, W.J.; Ju, C.; Kim, K. H.; Char, K. High Mobility in a Stable Transparent Perovskite Oxide. Appl. Phys. Express 2012, 5, 061102. 20. Kim, H. J.; Kim, U.; Kim, T. H.; Kim, J.; Kim, H. M.; Jeon, B.-G.; Lee, W.-J.; Mun, H. S.; Hong, K. T.; Yu, J.; Char, K; Kim, K. H. Physical Properties of Transparent Perovskite Oxides (Ba,La)SnO3 with High Electrical Mobility at Room Temperature. Phys. Rev. B 2012, 86, 165205. 21. Shin, S. S.; Yeom, E. J.; Yang, W. S.; Hur, S.; Kim, M. G.; Im, J.; Seo, J.; Noh, J. H.; Seok, S. I. Colloidally Prepared La-doped BaSnO3 Electrodes for Efficient, Photostable Perovskite Solar Cells. Science 2017, 356, 167–171. 22. Singh, D. J.; Papaconstantopoulos, D. A.; Julien, J. P.; CyrotLackmann, F. Electronic Structure of Ba(Sn,Sb)O3: Absence of Superconductivity. Phys. Rev. B 1991, 44, 9519–9523. 23. Kim, U.; Park, C.; Ha, T.; Kim, R.; Mun, H. S.; Kim, H. M.; Kim, H. J.; Kim, T. H.; Kim, N.; Yu, J.; Kim, K. H.; Kim, J. H.; Char, K. Dopant-Site-Dependent Scattering by Dislocations in Epitaxial Films of Perovskite Semiconductor BaSnO3. APL Mater. 2014, 2, 056107. 24. Wang, H. F.; Liu, Q. Z.; Chen, F.; Gao, G. Y.; Wu, W.; Chen, X. H. Transparent and Conductive Oxide Films with the Perovskite Structure: La- and Sb-Doped BaSnO3. J. Appl. Phys. 2007, 101, 106105. 25. Wadekar, P. V.; Alaria, J.; O’Sullivan, M.; Flack, N. L. O.; Manning, T. D.; Phillips, L. J.; Durose, K.; Lozano, O.; Lucas, S.; Claridge, J. B.; Rosseinsky, M. J. Improved Electrical


26

Page 27 of 37 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Mobility in Highly Epitaxial La:BaSnO3 films on SmScO3 (110) substrates. Appl. Phys. Lett. 2014, 105, 052104. 26. Wei, R. H.; Tang, X. W.; Hui, Z. Z.; Luo, X.; Dai, J. M.; Yang, J.; Song, W. H.; Chen, L.; Zhu, X. G.; Zhu, X. B.; Sun, Y. P. Solution Processing of Transparent Conducting Epitaxial La:BaSnO3 Films with Improved Electrical Mobility. Appl. Phys. Lett. 2015, 106, 101906. 27. Cava, R. J.; Gammel, P.; Batlogg, B.; Krajewski, J. J.; Peck, W. F.; Rupp, L. W.; Felder, R.; van Dover, R. B. Nonsuperconducting BaSn1-xSbxO3: The 5s-Orbital Analog of BaPb1-xBixO3. Phys. Rev. B 1990, 42, 4815–4818. 28. Huang, T.; Nakamura, T.; Itoh, M.; Inaguma, Y.; Ishiyama, O. Electrical Properties of BaSnO3 in Substitution of Antimony for Tin and Lanthanum for Barium. J. Mater. Sci. 1995, 30, 1556–1560. 29. Mizoguchi, H.; Chen, P.; Boolchand, P.; Ksenofontov, V.; Felser, C.; Barnes, P. W.; Woodward, P. M. Electrical and Optical Properties of Sb-Doped BaSnO3. Chem. Mater. 2013, 25, 3858–3866. 30. Kim, H. J.; Kim, J.; Kim, T. H.; Lee, W.-J.; Jeon, B.-G.; Park, J.-Y.; Choi, W. S.; Jeong, D. W.; Lee, S. H.; Yu, J.; Noh, T. W.; Kim, K. H. Indications of Strong Neutral Impurity Scattering in Ba(Sn,Sb)O3 Single Crystals. Phys. Rev. B 2013, 88, 125204. 31. Liu, Q.; Dai, J.; Liu, Z.; Zhang, X.; Zhu, G.; Ding, G. Electrical and Optical Properties of SbDoped BaSnO3 Epitaxial Films Grown by Pulsed Laser Deposition. J. Phys. D: Appl. Phys. 2010, 43, 455401. 32. Schwartz, R. W.; Schneller, T.; Waser, R. Chemical Solution Deposition of Electronic Oxide Films. C. R. Chimie 2004, 7, 433–461.


27


Page 28 of 37

33. Subramanyam, G.; Cole, M. W.; Sun, N. X.; Kalkur, T. S.; Sbrockey, N. M.; Tompa, G. S.; Guo, X.; Chen, C.; Alpay, S. P.; Rossetti, G. A.; Dayal, K.; Chen, L.-Q.; Schlom, D. G. Challenges and Opportunities for Multi-Functional Oxide Thin Films for Voltage Tunable Radio Frequency/Microwave Components. J. Appl. Phys. 2013, 114, 191301. 34. Sarath Kumar, S. R.; Barasheed, A. Z.; Alshareef, H. N. High Temperature Thermoelectric Properties of Strontium Titanate Thin Films with Oxygen Vacancy and Niobium Doping. ACS Appl. Mater. Interfaces 2013, 5, 7268–7273. 35. Kim, H.; Horwitz, J. S.; Kim, W. H.; Mäkinen, A. J.; Kafafi, Z. H.; Chrisey, D. B. Doped ZnO Thin Films as Anode Materials for Organic Light-Emitting Diodes. Thin Solid Films 2002, 420–421, 539–543. 36. Cai, S.; Li, Y.; Chen, X.; Ma, Y.; Liu, X.; He, Y. Optical and Electrical Properties of TaDoped ZnSnO3 Transparent Conducting Films by Sol–Gel. J. Mater. Sci.: Mater. Electron. 2016, 27, 6166–6174. 37. Bermudez, V. M.; Berry, A. D.; Kim, H.; Pique, A. Functionalization of Indium Tin Oxide. Langmuir 2006, 22, 11113−11125.


28

Page 29 of 37 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


TOC Graphic


29


Figure 1. (a) A sketch of the preparation of BaSnO3-δ thin films by chemical solution deposition. (b)-(d) Three selected XRD patterns (left), rocking curves (middle) and Φ-scanning results (right) of BaSnO3-δ thin films with identical coatings synthesized by different annealing processes. (e) A schematic diagram for epitaxial relationship between the BaSnO3-δ thin film and the SrTiO3 substrate. (f) Cross-sectional TEM image near the thin film-substrate interface for the BaSnO3-δ thin film prepared by the MA&PA process. (g) Selected-area electron diffraction pattern for the MA&PA-processed BaSnO3-δ thin film combined with the SrTiO3 substrate, in which different crystallographic planes are marked. 147x135mm (300 x 300 DPI)


Page 30 of 37

Page 31 of 37 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 2. (a)-(f) FE-SEM images for crystallized BaSnO3-δ thin films fabricated by the SA, the MA as well as the MA&PA processes. (g) and (h) The detailed schematic diagrams of the BaSnO3-δ thin film fabrication processes including the SA, MA and further the PA, where the (g) denotes the SA and further PA process while the (h) gives the MA and further the PA process. 70x30mm (300 x 300 DPI)



Figure 3. (a) Magnified (200) diffraction peaks for all Sb-doped BaSnO3-δ thin films. (b) Evolution of lattice constant, FWHM value of rocking curve for (200) peak, and average FWHM value of Φ-scanning in response to Sb doping content for all derived thin films. (c)-(h) FE-SEM images for BaSn1-xSbxO3-δ (x=0.03, 0.06, 0.09, 0.12, 0.15, and 0.20) thin films. 64x25mm (300 x 300 DPI)


Page 32 of 37

Page 33 of 37 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 4. Optical transmittance results for all Sb-doped BaSnO3-δ thin films. The inset shows the calculated average optical transmittance in the visible region. 68x55mm (300 x 300 DPI)



Figure 5. Temperature dependent electrical conductivity of BaSn1-xSbxO3-δ (x=0.03, 0.06, 0.09, 0.12, 0.15, and 0.20) thin films prepared by different processes. 64x48mm (300 x 300 DPI)


Page 34 of 37

Page 35 of 37 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 6. Evolution of room temperature (T=300K) electrical conductivity with respect to Sb doping content (a), Hall results (b), Sb content dependence of room temperature carrier density (c) and mobility (d) for all BaSn1-xSbxO3-δ (x=0.03, 0.06, 0.09, 0.12, 0.15, and 0.20) thin films. 127x101mm (300 x 300 DPI)



Figure 7. XPS of BaSn1-xSbxO3-δ thin films within Ba 3d region (a), Sn 3d region (b), Sb 3d and O 1s regions (c). (d)-(h) Evolution of Sn2+, Sn4+ in crystal lattice, Sn4+ adjacent to oxygen vacancy, oxygen adjacent to Sn2+ (O-Sn), and oxygen vacancy in response to Sb doping content, which are deduced by the fitting results of XPS spectra as shown in (b) and (c). 97x53mm (300 x 300 DPI)


Page 36 of 37

Page 37 of 37 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


35x15mm (300 x 300 DPI)


Growth, Microstructures, and Optoelectronic Properties of Epitaxial

Recommend Documents