Effect of Atomic Layer Deposition Temperature on the Growth

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Effect of Atomic Layer Deposition Temperature on the Growth Orientation, Morphology, and Electrical, Optical, and BandStructural Properties of ZnO and Fluorine-Doped ZnO Thin Films Kyung-Mun Kang, and Hyung-Ho Park J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.7b08943 • Publication Date (Web): 07 Dec 2017 Downloaded from http://pubs.acs.org on December 11, 2017

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The Journal of Physical Chemistry

Effect of Atomic Layer Deposition Temperature on the Growth Orientation, Morphology, and Electrical, Optical, and Band-Structural Properties of ZnO and Fluorine-Doped ZnO Thin Films Kyung-Mun Kang and Hyung-Ho Park*

Department of Materials Science and Engineering, Yonsei University, Seoul 03722, Republic of Korea

ABSTRACT

The deposition temperature has a significant effect on the growth and physico-chemical properties of ZnO thin films. However, changes within a low temperature range have not yet been fully investigated. In this study, ZnO and fluorine-doped (F-doped) ZnO (ZnO:F) thin films were synthesized on glass substrates by atomic layer deposition, and the effect of deposition temperature (80 to 160 °C) on the crystallization behavior and electrical, optical, and band-structural properties of the thin films were analyzed. During deposition, a constant fluorine concentration was maintained in the anionic pulse gas by employing a 200:1 (vol/vol) mixing ratio of deionized water to hydrofluoric acid. We found that c-axis growth was preferred with ZnO thin films, while a-axis growth was

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preferred for ZnO:F thin films. An enhancement in the carrier concentration was also observed in both thin films with increase in the deposition temperature. In addition, the optical transmittance of ZnO:F thin films was slightly higher than that of ZnO thin films, and this transmittance decreased with increasing deposition temperature. More significantly, F-doping led to a larger optical band gap in ZnO:F thin films than in ZnO thin films due to an increase in the carrier concentration with F-doping.

INTRODUCTION ZnO has received considerable attention in recent years as a challenging material for application in the field of semiconductor.1–6 More specifically, ZnO is a direct gap semiconductor (3.37 eV) with a hexagonal wurtzite structure and an exciton binding energy of 60 meV, which is higher than the thermal energy at room temperature.7 In addition, it possess better chemical and thermal stability and wide availability makes it a strong candidate material for a wide range of uses, including ultraviolet (UV) emitters and detectors, gas sensors, and transparent conducting electrodes.1,2 Furthermore, ZnO can be doped with a wide variety of ions to meet the demands of several applications. For example, due to the low electron concentration (i.e., 1018–1019 cm−3) of intrinsic ZnO compared to In2O3:Sn (ITO) (~1021 cm−3), recent studies have investigated to enhance electron concentration through an addition of trivalent cations (B, Ga, Al)8–10 or halogen anions (Cl, F).11,12 This enables preparation of degenerately doped semiconductors exhibiting high electron concentrations (i.e., ≤1021 cm−3), with sustaining high electron mobility.


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Amongst the different dopants available for the ZnO matrix, F appears to be the most effective. For example, comparison of fluorine doped (F-doped) ZnO (ZnO:F) films with similar metal doped ZnO films indicates that the electronic perturbation is mainly confined to the filled valence band when flourine substitutes oxygen. In addition, a reduction in the scattering of conduction electrons decreases resistivity and helps to enhance mobility in the ZnO:F film.11 Furthermore, as F ions are similar in size to O ions, F is predicted to be an n-type dopant capable of maintaining a high electron mobility in ZnO deprived of any lattice distortion.13 Further benefits of ZnO:F films are a decrease in the recognized number of Os2−/Os− surface states, with an increased carrier mobility through F passivation.14 As a result, the doping efficiency of F in ZnO is greater than that of metallic cation dopants, allowing optimization of the electrical conductivity.15

In terms of the preparation of ZnO thin films, a range of deposition techniques have been employed, including vacuum evaporation, pulsed laser deposition, sol-gel preparation, chemical vapor deposition, molecular beam epitaxy, magnetron sputtering deposition, and atomic layer deposition (ALD).16–20 Among these various processes, ALD is considered an advanced deposition method for low temperature processing, which results in the formation of highly uniform films.21–24 More specifically, the ALD method is a coating development process involving self-controlling surface interaction, and consists of a repetitive pulse production and purging method using desired precursors. In addition, this technique allows the isolation of source materials throughout the complete deposition process. As such, this technique permits a deposition at low temperature with good step coverage (high aspect ratio), high uniformity with controlled film thickness by regulating number of ALD



pulse. Also, separate dosing of precursors avoids vapor phase reactions, this permits the use of highly reactive precursors, and affords enough time for completion of each reaction step. These outstanding assets allow the deposition of thin films with complex 3D structures and processing at relatively low temperatures, thereby simplifying the use of flexible substrates.

Physical properties of ZnO films are usually dependent on a range of deposition factors, including the pulse time, the number of ALD cycles, and the substrate temperature. Among these parameters, the deposition temperature has a significant effect on the growth rate, crystal structure, preferred growth orientation, and electrical properties of resulting ZnO films.25–27 For example, A. Wójcik et al.28 reported that an increase in deposition temperature from 280 to 400 °C induced a change in the preferential orientation from c-axis normal to c-axis parallel during growth of the ZnO film. However, the effect of low deposition temperatures has yet to be investigated, and no comparative studies have been performed between ZnO and F-doped ZnO coatings. Thus, we herein report the preparation of ZnO and ZnO:F coatings by ALD, and a subsequent investigation of the effect of deposition temperature on the structural, electrical, and optical properties of the resulting films.

EXPERIMENTAL SECTION ZnO and ZnO:F thin films were deposited on Si and LCD glass (Fusion 1737) substrates using ALD via a traveling wave type Lucida D100 system (NCD Technology, Inc. Korea) at a range of deposition temperatures (i.e., 80, 100, 120, 140, and 160 °C) and a working pressure of ~1 Torr.


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Diethylzinc (DEZ) was obtained from Hansol Chemical Co., Ltd., Korea. DEZ was used as precursors for Zn and deionized water (DI water) for O. The in-house fluorine was prepared by mixing DI water (50 mL) with diluted hydrogen fluoride (HF, 0.5 mL, 48–51% aqueous solution), as described in our previous study.29 DEZ was at 10 °C using a chiller to lower the reaction rate, and was transported into the reaction chamber by using high purity N2 (99.999%) with a 20 SCCM flow rate. The ALD progressive cycles were employed for ZnO and ZnO:F thin films as follows: DEZ pulse (0.1 s), N2 purge (10 s), H2O (or H2O/HF mixture) pulse (0.1 s), N2 purge (10 s) (Fig. S1). During deposition, a constant fluorine concentration was maintained in the anionic pulse gas by employing a 200:1 (vol/vol) mixing ratio of deionized water to hydrofluoric acid. Film samples were prepared using a range of deposition temperatures (i.e., 80, 100, 120, 140, and 160 °C), and the resulting films were designated as ZnO(80), ZnO:F(80), etc., where the number in parentheses represents the deposition temperature.

The crystal structures and surface morphologies of undoped ZnO and ZnO:F films were then studied by X-ray diffraction (XRD, 2000-D/MAX, Rigaku) using CuKα radiation (α = 1.5418 Å) and field emission scanning electron microscopy (FE-SEM, Hitachi, S-4800). The photoluminescence (PL) spectroscopy (Hitachi P7000) was performed in the range of 200 to 700 nm at room tempeature. An elemental analysis of films was analyzed by X-ray photoelectron spectroscopy (XPS; Thermo VG, UK) with monochromated Al X-ray sources (Al kα line: 1486.6 eV). Grazing incident wide-angle Xray diffraction (GIWAXD) was also performed by the 9A beam line available at the Pohang Accelerator Laboratory (PLS). The van der Pauw method was used for the measurement of electrical



performance (i.e. resistivity (r) and Hall coefficient (RH)) of films. The results were obtained using a Hall Effect measurement system (Ecopia HMS 3000, Korea) at room temperature. The four-probe method at ≤0.57 T magnetic field were employed for the measurement of electrical components using a direct current (DC current = 10 mA). Due to the high quality of the films, this measurement was carried out in absence of direct metal electrical contacts. UV-vis-NIR spectrophotometry (V-570, JASCO) were used to obtain transmittance spectra between 200 and 2500 nm wavelength range. Ultraviolet photoelectron spectroscopy (UPS) study was carried out by He I (21.22 eV) radiation with a bias voltage of −5 V in the 4D beam line of the PLS. For the calibration of the energy shift, Au foil was used as a reference material.

RESULTS AND DISCUSSION The crystal structures of ZnO and F-doped ZnO films prepared on glass slides at a range of deposition temperatures were analyzed by XRD (Fig. 1). Diffraction peaks of all samples were indexed by comparing them with a standard reference XRD pattern of a hexagonal wurtzite ZnO structure. Changes in the preferential growth orientations of ZnO and F-doped ZnO thin films (i.e., inbetween (002) and (100)) can be explained in the context of F doping. More specifically, preferential (002) for ZnO and (100) for ZnO:F growth orientations were observed in thin films. Although growth orientation (002) is well known in ZnO thin films, the change in preferred growth orientation to (100) for ZnO:F was associated with the filling of O vacancies or the substitution of O sites with F anions.30 Indeed, Liu et al. and Janotti et al. reported first-principle analysis of F-doped ZnO, and concluded the best advantageous sites for the F dopant in the ZnO material are vacant O sites. Because of its


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lowest formation energy and thereby behave as the principal defect species.31,32 The growth oriented along a-axis, plane (100) is more active than the growth oriented along c-axis (200) plane which is parallel to the thin film. It is expected due to O vacancies or substituting O sites with F− anions. However, no changes in the peak positions resulting from such vacancy filling or substitution were observed, likely due to the small amount of O vacancies31 and the similar ionic radii of the F− (~1.31 Å) and O2− (~1.34 Å) ions.30,34 As a result, almost no change in lattice parameters was observed upon F doping, as indicated in Table 1. To confirm the decrease in ZnO oxygen vacancies upon doping with F, the room temperature photoluminescence spectra (PL)

of the ZnO and F-doped ZnO substrates deposited at various

temperatures were studied under the excitation of a 266-nm laser, as shown in Figs. 2, S2, and S3. The UV signal at ~387 nm originates from near-band-edge emission of crystalline ZnO, while the broad peak at ~500 nm can be assigned to radiative recombination, of O vacancies and Zn interstitials in the ZnO films at deep-level defects.32,35 In addition, the luminescent band at 500 nm, originating from the defect sites, decreased with increasing deposition temperature from 80 to 160 °C. This shows that the crystalline nature of the ZnO film improves with a decrease in defect density upon increasing the deposition temperature. Furthermore, the ZnO:F thin films exhibited a relatively noteworthy decrease in the strength of visible (~500 nm) emissions, likely as a result of a reduction in O vacancies, which are assigned to F ions occupying the vacant sites of ZnO matrix. Hence, the significant decrease in the strength of visible light is a result of lessening in the amount of defects through F doping can be concluded from these studies.



The detailed chemical bonding structure of O in ZnO films were analyzed using XPS in the O1s region (Fig. 3). The O1s peak composed by three constitutional peaks at OI (530.5 eV), OII (531.8 eV), and OIII (532.8 eV). The OI and OII can be allocated to fully-ionized O2- ion and VO chemical states in the ZnO lattice, respectively. Further, the binding energy peak located at higher energy, OIII belongs to oxygen aroused from hydroxyl group bonded to Zn atom (HO-Zn).36-38 For the well understanding, the comparative integrated intensity fraction of VO and hydroxide (M-OH) is shown in Figs. 3c and 3d as a function of deposition temperature. With an increase in deposition temperature, the integrated area of the VO state decreased more monotonically than the areas of the hydroxide state. This result suggests that F anions first filled VO sites, then due to the strong electronegativity of F, formed hydrogen bonds with hydroxyl groups. The F composition of F-doped ZnO thin films according to deposition temperature was also obtained by XPS. With increasing in the deposition temperature from 80 to 160°C, the atomic concentration of F in the films increased slightly. All parameters of F concentrations in ZnO films are indicated in Table S1. From this table, we can observe the effect of deposition temperature on dopant concentration in the ZnO films. The surface morphology of ZnO and ZnO:F thin films deposited on the glass substrates were then examined using FE-SEM, and the resulting images are shown in Figs. 4 and S4. Generally, along caxis (002) and a-axis (100) growth orientations, columnar and wedge-like morphologies are observed, respectively.39 Thus, the XRD (Fig. 1a) and SEM observations (Figs. 4(1a–1c) and S4(1a, 1b)) indicate that c-axis growth was preferred for the ZnO thin films. For F-doped ZnO thin films, the number of grains oriented along c-axis decreased with increasing deposition temperature, while the


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number of a-axis-oriented grains increased (Figs. 4(2a–2c) and S4(2a, 2b)). It is possible that this temperature-dependent morphological change may be a effect of the F doping mechanism itself. To measure the electrical parameters of the ZnO and ZnO:F films prepared at a range of deposition temperatures, Hall measurements were performed on the films deposited on glass slides using the van der Pauw method. Figures 5a, 5b, and 5c depict plots of the carrier concentration, Hall mobility, and resistivity of the films with increasing deposition temperature, respectively. Increasing the deposition temperature led to a gradual increase in carrier concentration, and the ZnO:F thin films exhibited higher carrier concentrations than the undoped ZnO. Due to less formation energy associated with O vacancies, these are favorable doping sites for F− ions, which have comparable ionic radii to the O2− ions. Such substitution of O instead of Zn prevents perturbation of the conduction band and, as examined later in the morphological analysis, the passivation effect of F on grain boundary defects also causes an increase in carrier mobility.39 Indeed, in thin films of ZnO, the high number of grain boundary defects can easily trap free electron carriers, thereby decreasing their mobility, leading to an increase in resistivity.39 Thus, through saturation of grain boundary effects by F anions, this passivation effect may increase the conductivity of ZnO:F films through an increase in carrier concentration and mobility, and by preventing the perturbation effect. As the deposition temperature was increased, the electron mobility of the film increased, likely due to an enhancement in film crystallinity and an increase in grain size, as conversed in the context of XRD data. Indeed, it is well known that larger grain sizes, result in lesser grain boundary areas behaving as carrier scattering centers, are more effective at increasing carrier mobility. Therefore, the carrier mobility in



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the crystal can be enhanced by increasing the deposition temperature due to the increase in grain size (Table 1). In each case, the corresponding grain size was calculated using the Scherrer equation.40 Figure 6 displays the optical transmittance of the prepared ZnO and F-doped ZnO thin films within wavelength of 200 to 2500 nm (Figs. 6a and 6b), and an enlargement of the transmittance in the visible range between 200 and 1000 nm (Figs. 6c and 6d). In transparent conductive oxide films, the optical transmittance can be divided into three key regions: UV, visible, and NIR. By increasing the carrier concentrations of the films through F-doping, absorption is enhanced in the NIR region (Fig. S5). The reasoning of such phenomenon can be described by the classical Drude free-electron theory.41 More specifically, absorption by free electrons limits the transmittance of films with high electron densities in the conduction band, resulting in an increase in the absorption and reflection of electron gas (plasmon), and for the frequencies lesser than the plasma frequency (i.e., for wavelengths higher than the plasma wavelength), a corresponding decrease in transmittance can be observed. This can be represented as follows: =

∗

=

(1) (2)

where is the plasma frequency; n is the electron concentration; e is the charge of on electron; and are dielectric constants measured in the transparent region of the spectrum of an undoped ZnO and the vacuum permittivity, respectively; is the plasma wavelength; and c is the velocity of light in a vacuum.42 Hence, increasing the carrier concentration through an increase in deposition temperature increases absorption of the films by shortening the plasma wavelength. These results


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were well matched with the electrical properties of the prepared ZnO and F-doped ZnO films. As indicated in Figs. 6c and 6d and in Table 1, all ZnO and ZnO:F films exhibited a transmittance >80% in the visible region. The absorption coefficients were estimated using Lambert’s formula to provide detailed optical performance of ZnO and ZnO:F samples in the UV region by following formula:

α = 1 / t[ln(1/Tr)]

(3)

where Tr and t are the transmittance and film thickness, respectively.43 The direct band gap energy of each films were calculated from a plot of (αhv)2 vs. hv, called as a Tauc plot, by extrapolating the linear region at α = 0, as shown in the insets of Figs. 6c and 6d. As also indicated in Table 1, the calculated optical band gap values was increased with an increase in the carrier concentrations of ZnO and ZnO:F thin films. In addition, with increasing the deposition temperature, the shift in the absorption edge was found to be increased. Furthermore, the band gap values of ZnO thin films corresponded with the ideal band gap of pure ZnO, i.e., 3.37 eV,44 and the band gapenhancement with increasing deposition temperature is assumed from the Burstein-Moss effect.45,46 As ZnO films are naturally n-type oxide semiconductors, owing to natural O vacancies and Zn interstitials, which generate electron donors. And the addition of donor F− anions moves the Fermi level of ZnO:F films in the conduction band, causing the films bacome totally degenerate; therefore, the absorption edge transfers to higher energies than the real band gap of pure ZnO. Thus, the gradual enhancement in absorption in the NIR region, and in the optical bandgap of the UV region, can be considered further confirmation of the increase in electron concentration caused by doping the ZnO films.



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Figure 7 shows the UPS spectra of the low kinetic energy cutoff region and the valence band region of ZnO and ZnO:F films. The spectra were recorded with a 5.0 V sample bias to ensure that the sample inelastic cutoff could be notable, as indicated in Figure 7. The Fermi energy (EF) of the films was 21.35 eV, and their work function values were determined using the following equation (see also Table 1): Φ = hν + Ecutoff − EF

(4)

As outlined in the Table 1, the values of work function for ZnO and F-doped ZnO thin films increased slightly with increasing deposition temperature due to an increase in carrier concentration, as shown in Fig. 5(a). In addition, the work function values of ZnO:F thin films were slightly higher than those of undoped ZnO thin films, due to F doping in the ZnO. From the above results, we can conclude that our approach for fabricating textured ZnO:F films is suitable for light-trapping applications employing a single-step process without applying wet chemical etching. Our approach can also be adopted for flexible substrates that need a low deposition temperature.47

CONCLUSIONS In this study, we reported the successful deposition of undoped ZnO and fluorine-doped (Fdoped) ZnO:F thin films on Si and LCD glass substrates by atomic layer deposition (ALD) over a range of deposition temperatures. Interestingly, ZnO thin films showed preferred growth in the c-axis direction, while ZnO:F thin films exhibited a change in growth orientation from c-axis to a-axis growth. This phenomenon was caused by F-doping, and can be clarified by the filling of O vacant


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sites and the replacement of O sites with F anions. These results agreed with photoluminescence observations. Furthermore, the growth mechanism of F-doped ZnO thin films was confirmed by FESEM and GIWAXD analyses. Indeed, we found that the grain sizes of ZnO and ZnO:F thin films tended to increase with increasing deposition temperature, thereby increasing the carrier mobility and decreasing the resistivity of the films. However, the smaller resistivity of ZnO:F thin films compared to ZnO thin films was also due to the passivation effect of electronic states, and the increased carrier concentration due to F doping. This direct F doping effect was enhanced for high temperaturesynthesized ZnO:F thin films because of the deposition temperature dependent F doping concentration. In addition, the optical transmittance of ZnO:F films was slightly larger than that of ZnO films. More specifically, the optical band gap of ZnO is smaller than the bulk Eg of 3.37 eV, while the band gap energies of ZnO:F films deposited at all examined temperatures were larger than that of bulk ZnO. This increase in band gap with increasing deposition temperature is believed to be due to the Burstein-Moss effect. The above results therefore indicate that the structural, electrical, and optical properties of ZnO thin films are closely related to both the doping of F and the deposition temperature employed during the ALD process.

FIGURE CAPTIONS Figure 1. Thin-film XRD patterns of (a) undoped and (b) F-doped ZnO films grown on glass substrates at a range of deposition temperatures.



Figure 2. PL spectra of (a) undoped ZnO and (b) F-doped ZnO thin films deposited on glass substrates at a range of deposition temperatures.

Figure. 3. XPS O1s spectra for (a) undoped ZnO and (b) F-doped ZnO thin films for various deposition temperatures. Portion of oxygen vacancies and hydroxides related to bonding constitution in O 1s of (c) undoped ZnO and (d) F-doped ZnO thin films as a function of deposition temperature.

Figure 4. Top-view FE-SEM images of [(1a)–(1c)] undoped and [(2a)–(2c)] F-doped ZnO films grown at a range of deposition temperatures: (1a) ZnO(80), (1b) ZnO(120), (1c) ZnO(160), (2a) ZnO:F(80), (2b) ZnO:F(120), and (2c) ZnO:F(160). All scale bars = 100 nm.

Figure 5. (a) Carrier concentrations, (b) Hall mobilities, and (c) resistivity of the undoped ZnO and Fdoped ZnO deposited on glass substrates at a range of deposition temperatures.

Figure 6. Optical transmittance curves between 250 and 2500 nm for (a) undoped ZnO and (b) Fdoped ZnO films prepared at a range of deposition temperatures. Also shown are enlarged sections of the transmittance curves in the visible range for (c) undoped ZnO and (d) ZnO:F films prepared at a range of deposition temperatures. The inset plots were used to evaluate the optical band gaps of the films.

Figure 7. UPS spectra of low kinetic energy cutoff regions and valence band regions of (a) undoped ZnO and (b) F-doped ZnO films prepared at a range of deposition temperatures.


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TABLE

Table 1. Film thickness, growth rate, lattice parameters, lattice volumes, grain sizes, transmittances, optical band gaps, and work function values of ZnO and ZnO:F thin films.

ASSOCIATED CONTENT

Supporting Information.

The Supporting Information is obtainable free of charge on the ACS Publications website at DOI

AUTHOR INFORMATION Corresponding Author *

E-mail: [email protected]. Tel.: +82-2-2123-2853. Fax: +82-2-312-5375.

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (No. 2015R1A2A1A15054541). This material is based upon work supported by the Ministry of Trade, Industry & Energy (MOTIE, Korea) under the Industrial Strategic



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Technology Development Program, No. 10068075, 'Development of Mott-transition based formingless non-volatile resistive switching memory & array'.

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Table 1. Film thickness, growth rate, lattice parameters, lattice volumes, grain sizes, transmittances, optical bandgaps, and work function values of ZnO and ZnO:F thin films.

Sample I.D.

ZnO (80)

ZnO (100)

ZnO (120)

ZnO (140)

ZnO (160)

ZnO:F (80)

ZnO:F (100)

ZnO:F (120)

ZnO:F (140)

ZnO:F (160)

Film thickness (nm)

232.4 ± 5

234.4 ± 5

239.6 ± 5

244.8 ± 5

247.9 ± 5

233.3 ± 5

238.3 ± 5

242.1 ± 5

248.7 ± 5

249.4 ± 5

Growth rate (nm/cycle)

0.193 ±0.005

0.195 ± 0.005

0.199 ± 0.005

0.204 ± 0.005

0.206 ± 0.005

0.194 ± 0.005

0.198 ± 0.005

0.202 ± 0.005

0.207 ± 0.005

0.208 ± 0.005

Lattice parameter a (Å) / c (Å)

3.255 ± 0.1 / 5.202 ± 0.1

3.255 ± 0.1 / 5.193 ± 0.1

3.252 ± 0.1 / 5.203 ± 0.1

3.251 ± 0.1 / 5.195 ± 0.1

3.254 ± 0.1 / 5.187 ± 0.1

3.254 ± 0.1 / 5.204 ± 0.1

3.258 ± 0.1 / 5.200 ± 0.1

3.250 ± 0.1 / 5.195 ± 0.1

3.250 ± 0.1 / 5.191 ± 0.1

3.256 ± 0.1 / 5.192 ± 0.1

47.73 ± 0.0001

47.64 ± 0.0001

47.66 ± 0.0001

47.55 ± 0.0001

47.56 ± 0.0001

47.73 ± 0.0001

47.79 ± 0.0001

47.52 ± 0.0001

47.50 ± 0.0001

47.67 ± 0.0001

Grain size (Å)

19.86 ± 0.1

22.09 ± 0.1

28.57 ± 0.1

29.44 ± 0.1

27.29 ± 0.1

21.56± 0.1

24.04 ± 0.1

31.27 ± 0.1

31.14 ± 0.1

29.34 ± 0.1

Transmittance (%)

80.6 ± 0.1

82.7 ± 0.1

82.7 ± 0.1

82.3 ± 0.1

79.5 ± 0.1

81.6 ± 0.1

83.0 ± 0.1

83.4 ± 0.1

81.5 ± 0.1

80.4 ± 0.1

Optical bandgap (eV)

3.261 ± 0.06

3.265 ± 0.06

3.268 ± 0.06

3.277 ± 0.06

3.279 ± 0.06

3.264 ± 0.06

3.296 ± 0.06

3.312 ± 0.06

3.331 ± 0.06

3.347 ± 0.06

4.41 ± 0.01

4.41 ± 0.01

4.42 ± 0.01

4.48 ± 0.01

4.49 ± 0.01

4.49 ± 0.01

4.50 ± 0.01

4.51 ± 0.01

4.53 ± 0.01

4.57 ± 0.01

Lattice volume (Å3)

Work function (eV)



Figure 1


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Figure 2



Figure 3


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Figure 4



Figure 5


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Figure 6



Figure 7


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SYNOPSIS


Effect of Atomic Layer Deposition Temperature on the Growth

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