Indium oxide thin film prepared by low temperature atomic layer deposition using liquid precursors and ozone oxidant

Accepted Manuscript Indium oxide thin film prepared by low temperature atomic layer deposition using liquid precursors and ozone oxidant W.J. Maeng, Dong-Won Choi, Jozeph Park, Jin-Seong Park PII:

S0925-8388(15)30547-8

DOI:

10.1016/j.jallcom.2015.07.150

Reference:

JALCOM 34843

To appear in:

Journal of Alloys and Compounds

Received Date: 24 June 2015 Revised Date:

12 July 2015

Accepted Date: 18 July 2015

Please cite this article as: W.J. Maeng, D.-W. Choi, J. Park, J.-S. Park, Indium oxide thin film prepared by low temperature atomic layer deposition using liquid precursors and ozone oxidant, Journal of Alloys and Compounds (2015), doi: 10.1016/j.jallcom.2015.07.150. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Indium oxide thin film prepared by low temperature atomic layer deposition using liquid precursors and ozone oxidant

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Department of Materials Science and Engineering, University of Wisconsin Madison, Madison, Wisconsin 53706, USA

b

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W.J. Maenga1, Dong-Won Choib1, Jozeph Parkc*, and Jin-Seong Parkb*

Division of Materials Science and Engineering, 222 Wangsimni-ro, Seongdong-gu, Hanyang University, Seoul, Republic of Korea 133-719

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Department of Materials Science and Engineering, KAIST, Daejeon 305-701, Republic of Korea

Abstract

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Transparent conducting Indium oxide (InOx) thin films were deposited by atomic layer deposition at low deposition temperatures below 100 °C. For the comparative study with liquid precursors in low temperature

thermal

ALD,

diethyl[1,1,1-trimethyl-N-(trimethylsilyl)silanaminato]-Indium,

[3-

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(dimethylamino-kN)propyl-kC]dimethyl-Indium, and triethyl indium (TEIn) were used as the In precursors. Ozone was used as the oxidant for all precursors. InOx films grown using the three precursors all exhibit relatively low electrical resistivity below 10-3 Ωcm at temperatures above 150

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°C. Below 100 °C, the lowest resistivity (2×10-3 Ωcm) was observed in the films grown with TEIn. The electrical, structural and optical properties were systematically investigated as functions of the

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deposition temperature and precursors.

Keywords: indium oxide, atomic layer deposition, transparent conducting oxide, resistivity


These two authors contributed equally to this work.

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Current affiliation (Dr. Jozeph Park) is Samsung Display, Inc., Yongin-Si, Republic of Korea 446-920.

*Author to whom correspondence should be addressed; e-mail : [email protected] ; [email protected] I. Introduction 1

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Indium oxide thin films have been widely studied for applications as transparent conducting oxides (TCOs),1 semiconductors in thin film transistors,2 gas sensors,3 and catalysts.4 Of particular interest is the application of this material as a transparent electrode in the fields of transparent thin-

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film transistors (TFTs), organic light-emitting diodes (OLEDs) and photovoltaics.5-7 A high optical transmittance in the visible region (> 80%) is required in order to be applicable as a transparent electrode in the above devices, as well as a low electrical resistivity < 10-3 Ω·cm.8 Also, in order to

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enable the implementation of TCOs into flexible electronics based on polymer substrates, the film must be deposited at relatively low temperatures.

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The growth of indium oxide films usually involves vacuum-based methods such as pulsed laser deposition,9 sputtering,10, 11 and chemical vapor deposition.12, 13 Among those, atomic layer deposition (ALD) is a versatile technique, because it enables the growth of uniform and high quality thin films over relatively large areas while allowing precise control of the thickness and chemical composition.14 Also, the film formation can be carried out at relatively low temperatures. In that regard, ALD growth

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of indium oxide has been investigated by several research groups. However, most of the reported studies were based on solid In precursors, which exhibit relatively low vapor pressure and reproducibility although some of them readily volatilize with mild heating.15-17 In addition, precursors

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such as InCl3, indium acetylacetonate [In(acac)3]15 and trimethylindium (TMIn) require relatively high deposition temperatures and result in slow ALD growth rates 18, 19 and high electrical resistivity (>10-3

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Ω·cm).17, 20, 21 The use of cyclopentadienylindium (InCp) precursor resulted in relatively fast ALD growth (1.3 Å/cycle), but the deposition temperatures were still relatively high (200~300 °C)

22-24

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Also, high resistivity (~1.6×10-2 Ω·cm) films were obtained.22 The use of a liquid In precursor that requires low deposition temperatures is thus necessary, while allowing relatively fast growth of low resistivity films. Recently, we reported on the ALD of low resistivity (10-4 Ω·cm ~ 6.3×10-5 Ω·cm) InOx films grown with a new liquid precursor, Et2InN(TMS)2, and water as the oxidant.25 The ALD growth

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ACCEPTED MANUSCRIPT window was observed at relatively low temperatures (175 ~ 250 °C) with an optimum growth rate of approximately 0.7 Å/cycle. Further lowering of the deposition temperature is needed in order to apply this technique for mechanically flexible platforms. An alternative precursor, InCp, allows the use of relatively low deposition temperatures (~100 °C), however the injection of oxygen and H2O is

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required to stimulate the chemical reactions.23 In the present work, we report on the microstructure, electrical and optical properties of ALD-grown indium oxide films prepared using three different liquid precursors and ozone. For those films, ALD windows include relatively low temperatures, with

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reasonably high growth rates. Moreover, the deposited indium oxide films exhibit high conductivity

II. Experimental

Three

different

liquid

precursors

(trimethylsilyl)silanaminato]-Indium

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and high optical transparency in the visible range.

were

(INCA),

prepared,

namely

diethyl[1,1,1-trimethyl-N-

[3-(dimethylamino-kN)propyl-kC]dimethyl-Indium

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(DADI), and triethyl-indium (TEIn), supplied by UP Chemical Co., Ltd. (Pyeongtaek, Korea). The ball-stick model of precursor molecule and TG, DSC data of these three precursors is shown in Fig S1, and S2. For the deposition of indium oxide thin film, the above precursors were used as the indium

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source and ozone was used as the reactant gas. A viscous flow reactor (NCD Inc. D-100 model) was

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employed for the deposition of indium oxide films onto SiO2/Si substrates. N2 was used as the carrier and purging gas, for which separate inlets were used for each precursor and ozone. The N2 gas flow rate (50 sccm) was controlled by a mass flow controller. The thicknesses and refractive indices of the deposited films were measured by a spectroscopic ellipsometer (SE) (Woollam-VASE). The electrical resistivity, carrier concentration and Hall mobility were investigated by means of a Hall-effect measurement system (HK5500PC, Accent Optical Technology) using a van der Pauw configuration. To reduce the contact resistance, indium metal was used as the contact material at the four corners of each rectangular sample. The microstructure of the

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ACCEPTED MANUSCRIPT films was studied by X-ray diffraction (XRD) (Rigaku diffractometer Ultima IV) using a Cu Kα X-ray source. The chemical composition and chemical binding energies were investigated by X-ray photoelectron spectroscopy (XPS) (ESCA Lab 200R). The optical transmittance and band gap width were observed by ultraviolet-visible spectroscopy (UV-VIS) (Optizen-3220 UV). In order to analyze

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the electronic structure, X-ray absorption spectra (XAS) were carried out by a total electron yield mode on the beamline 10D at the Pohang Light Source (PLS). The resolution of the measurements was 0.1 eV at the O-K edge. To examine the characteristics of precursor, thermoGravimetry (TG,

Result and Discussion

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III.

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NETZSCH 209 F3) and differential scanning calorimetry (DSC, NETZSCH 200 F3) were conducted.

40 nm-thick indium oxide films were deposited onto SiO2/Si substrates using an ALD technique. The growth condition was examined by modifying the precursor and substrate temperatures (figures 1a and 1b). Figure 1a shows the ALD growth per cycle (GPC) as a function of precursor temperature

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while keeping the substrate temperature fixed at 200 oC. The GPC of the three precursors saturated at approximately 0.8 Å/cycle, 0.5 Å/cycle, and 0.6 Å/cycle respectively, at precursor temperatures above 30 oC. The increased temperature can indicate higher vapor pressure; therefore, ALD growth mode

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can be confirmed by these saturated GPC. The GPC values at substrate temperatures ranging from 50 to 250 °C are shown in Figure 1b. ALD process windows were found between 100 and 200 °C, where

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the GPCs remain constant. The results show higher GPCs and a growth window at lower temperatures compared to former reports on ALD indium oxide growth with H2O reactant using InCl3, In(acac)3, and TMIn.15, 18, 19, 23 Previously, the InCp precursor resulted in an ALD window beginning at 140 °C, which is a sufficiently low temperature for flexible devices, however the process required simultaneous injection of two reactants; water and oxygen.23 On the other hand, the current results presented herein show that the single ozone reactant allows the realization of ALD mode for all three precursors, for which the ALD window begins at approximately 100 °C. The lower limit of the growth window is lowered by almost 100 °C in comparison with previous studies that used the same O3 4

ACCEPTED MANUSCRIPT reactant with other precursors.15,16 Figures 2 a, b, and c show the resistivity, Hall mobility, and carrier concentration of indium oxide films deposited at different temperatures. The film properties of ALD InOx films grown using three kinds of precursors are summarized in Table 1. The resistivity values of each InOx thin film grown

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with three different precursors decrease monotonically with increasing deposition temperature from 100 °C to 200 °C. The resistivity values of InOx thin films from INCA and DADI deposited at 200 oC are lower than 10-3 Ωcm. These are approximately an order of magnitude lower than those obtained

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previous studies using InCp or In(acac) precursors with O315, 16, and of the same magnitude as those obtained with InCp with the combination of O2/H2O reactants.23 However, below 150 °C, the

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resistivity increases rapidly over 10-2 Ωcm. Even though this deposition temperature is lower than the reported values in previous ALD In2O3 work, more room is available for lower resistivity. Among the three precursors, the lowest resistivity was observed with TEIn, which is 8×10-5 Ωcm at a deposition temperature of 200 °C. This value is one or three orders of magnitudes lower than those previously reported for indium oxide grown with different precursors15, 16, 17, 19, 22, 25 or using alternative deposition

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methods such as sol-gel,1 sputtering,10, 26 and CVD.27, 28 By reducing the deposition temperature, despite the overall increase in resistivity for all films, that of indium oxide grown with DADI is lower

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than that deposited with INCA at 100 °C. At this temperature, the resistivity is close to 1×10-3 Ωcm, which is sufficiently low for TCO applications, and comparable with previous results where InCp was

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used with the combination of reactants H2O and O2.15 These results show that the InOx films grown with TEIn precursor with O3 reactant are suitable as TCOs at deposition temperature below 150 °C. The Hall mobility values of each films increase with increasing deposition temperature. The lowest mobility is observed for INCA, which is lower than 10 cm2/Vs even at a deposition temperature of 250 °C. The films grown with DADI exhibit rapidly increasing mobilities with respect to the deposition temperature. At low deposition temperatures, the mobility remains close to 10 cm2/Vs, and reach values approximately three times higher at 250 °C. The most drastic increase in mobility is observed with the TEIn precursor. The mobility increases by an order of magnitude as the 5

ACCEPTED MANUSCRIPT temperature is increased from 100 °C (5 cm2/Vs) to 250 °C (50 cm2/Vs). For the carrier concentrations, figure 2 c shows that the lowest value is obtained with the DADI precursor. The carrier concentration of InOx grown at 100 °C is close to that of semiconducting oxides (≈ 1018 cm-3). By increasing the deposition temperature, the carrier concentration values increase,

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however being still relatively low (< 1021 cm-3). These low carrier concentrations reflect the highest resistivity in the low deposition temperature region among the films grown with the three different precursors. The InOx grown with TEIn exhibits carrier concentrations near 1021 cm-3 at all deposition

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temperatures between 100~200 °C. These elevated carrier concentrations and high mobilities result in the best resistivity performance of all three films. The highest carrier concentration is observed in

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InOx grown with INCA, being approximately 2×1021 cm-3 at 100 °C and 8×1021 cm-3 at 200 oC. An interesting point is that the carrier concentrations decrease at 250 °C in the case of using INCA and TEIn. This may imply that the films have low concentrations of carrier generation sites related to point defects such as oxygen vacancies or In interstitials.29, 30 From the DSC data of INCA and TEIn

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(supplementary figures 2a and c), the decomposition temperature of the two precursors is close the deposition temperature of 250 °C, while the decomposition temperature of DADI is higher by almost 100 °C. Thus, INCA and TEIn are anticipated to readily decompose at 250 °C and undergo complete

may form.

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reaction with the O3 reactant. As a result, relatively defect-free films with low carrier concentrations

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The evolution of crystallinity and chemical bond states of the films deposited at 100-250 °C with the TEIn precursor are shown in figures 3 a and b. At 150 ℃, the XRD results show the presence of an amorphous phase, while indium oxide peaks begin to appear at 200 °C. This means that the InOx film grown with TEIn has a relatively low resistivity even with an amorphous structure. As the deposition temperature is increased, the indium oxide (222) peak becomes more intense, implying a larger fraction of the film being crystallized. Higher crystallinity at higher deposition temperatures may account for the increase in electrical mobility. The InOx thin films grown with the other two precursors exhibit similar structural characteristics with respect to the deposition temperature (Sup 3 a 6

ACCEPTED MANUSCRIPT and b). In figure 3 (b), the XPS O 1s peak can be deconvoluted into In-O and O-H bonds. The film deposited at 250 °C shows an almost symmetric single peak at 529.5 eV corresponding to the In-O binding energy of In2O3.32 However, the peak location shifts towards higher binding energies for films deposited at lower deposition temperatures. An additional peak is clearly observed at 531.3 eV for

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deposition temperatures of 100 and 50 °C, which corresponds to In-OH bond energy.31 This indicates that a fraction of indium is chemically bonding with hydroxides at low deposition temperatures. The increase of ALD growth rate at relatively low temperatures is well known to be related to the

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abundant formation of surface -OH groups.32 The decrease in carrier concentrations of ALD InOx can be explained by the decrease of oxygen vacancies due to the formation of –OH groups at low

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deposition temperatures.33

The change in carrier concentration with respect to deposition temperature can be attributed to the d orbital ordering, as observed in the XAS spectra. Figure 3 (c) shows the O K1 edge of InOx thin films grown with the TEIn precursor. Normalized oxygen K1 edge spectra were analyzed in order to examine the electronic structure of the conduction band in InOx. The relative intensities of the XAS

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peaks reflect the qualitative changes in molecular orbital bonding symmetry. The O K1 edge spectra of InOx are directly related to the oxygen p-projected states of the conduction band. Near the 535 eV peak, oxygen is bonded with the In 5sp hybridized orbital and near the 540 eV peak, oxygen is

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bonded with the In 5p orbital. At a deposition temperature of 100 °C, the peak does not exhibit clear crystal field splitting. However, at deposition temperatures above 150 °C, considerable crystal-field

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splitting occurs in the 5sp and 5p orbitals. This may be interpreted in such a way that higher deposition temperature induces better crystallinity and molecular orbital ordering. Especially for InOx, an oxygen deficient stoichiometry is expected to generate a considerable amount of oxygen vacant sites that contribute free electron carriers.25, 34 The spectroscopic data undergo the same trend for InOx films grown with all three different precursors. Figure 4 shows the optical bandgap of InOx thin films measured by spectroscopic ellipsometry. At temperatures above 150 °C, the bandgap is approximately 3.75~3.8 eV, which is close to the reported values for In2O3.36 This suggests that high quality InOx films with stoichiometry close to In2O3 can be 7

ACCEPTED MANUSCRIPT grown with all three precursors. Below 150 °C, the bandgap values of InOx films deposited with INCA and DADI exceed 4 eV, while for the TEIn precursor the bandgap still remains near 3.85 eV. At 50°C, the bandgap values of the InOx films grown with all three different precursors saturate at appoximately 4.5 eV, which is a much higher value than the reported bandgap of In2O3. The increase

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in bandgap energy in wide bandgap semiconductors or TCOs at low growth temperatures is usually interpreted by the quantum confinement effect. For the cases of ZnO and In2O3 films grown at relatively low temperatures, the nanocrystalline structure with extremely small grains would induce

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such size effect, which may result in increased bandgap energies.9, 36 However, in this work, the films maintain an amorphous structure, thus the quantum confinement effect is not applicable.

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Figure 5(a) shows the refractive index values of the InOx thin films grown with the three precursors at different deposition temperatures. The ideal refractive index of In2O3 is known to be approximately 2.05~2.15.37 All InOx thin films exhibit refractive indices almost identical to that of In2O3 at deposition temperatures above 150 °C. However, as the growth temperature decreases, the use of DADI and INCA result in significantly reduced refractive indices while in the case of TEIn the

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refractive index is still preserved at 100 °C. At 50 °C, the refractive index is below 1.8 regardless of the precursors. The refractive index is usually related to the carrier concentration or film density. However, the carrier concentration of the film grown with TEIn is slightly lower than that deposited

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with INCA, thus it may be suggested that the effect of film density is the main parameter. Low density

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materials are usually relatively more porous, and the porosity can be calculated by equation 1:

n p = (n 2 − 1)(1 −

P ) +1 100

(1)

Here, np is the refractive index of the porous material, n is the refractive index of the non-porous material, and P is the percentage of porosity. Figure 5 (b) shows the film porosity of the InOx thin films grown with the three precursors. The INCA and DADI films show almost no porosity at deposition temperatures above 150 °C, while porous films are obtained below that temperature. Porous films usually have relatively low dielectric constants and refractive indices because their atomic concentrations are lower. Thus, fewer atomic dipoles and carriers are present within the 8

ACCEPTED MANUSCRIPT material, with relatively high bandgap energy. At low deposition temperatures, the precursors cannot obtain sufficient energy to undergo the necessary chemical reactions. Also, the deposited atoms cannot obtain the energy required to relocate at energetically favorable sites. Thus, low deposition temperatures impede the atomic rearrangement and increase the film porosity. The TEIn precursor

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results in an almost perfect film down to a deposition temperature of 100 °C. This indicates that the reactivity with ozone is highest for TEIn, and reflects well the superior electrical properties of the film grown with TEIn at 100 °C.

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Figure 6 shows the transmittance of the InOx samples grown with TEIn at 50−250 °C. All films exhibit transmittance over 80% in the wavelength range of 500−700 nm. Especially, the transmittance

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values of InOx films deposited at low deposition temperatures (50 and 100 °C) at 550 nm are higher than 88 %, which makes them suitable for transparent electrodes. The films deposited above 100 °C have slightly lower transmittance values, however still higher than 80 % at 550 nm. The lower transmittance at higher growth temperatures may be related to the film density, which is in turn related

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to the refractive index.

Conclusion

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In summary, transparent indium oxide films with high conductivity were prepared by ALD using three different liquid precursors and ozone as the reactant. Every precursor exhibits ALD growth

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mode at temperatures above 100 °C. Films with electrical resistivity as low as 2×10-3 Ωcm were obtained when TEIn precursor is used at a relatively low deposition temperature of 100 °C. By analyzing the microstructure, optical bandgap and refractive indices, the indium oxide films grown with TEIn exhibit an amorphous structure, with the highest density and electrical performance at 100 °C. The latter is a sufficiently low temperature for mechanically flexible applications. Such film properties are attributed to the high reactivity of TEIn with ozone, which stimulates the chemical reactions to yield dense indium oxide films. The possibility of growing low resistivity oxide films by 9

ACCEPTED MANUSCRIPT ALD at 100 °C based on the combination of liquid precursors and ozone reactant opens up the possibility of forming TCOs onto large area substrates for flexible platforms including next generation

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displays and soft electronics.

Acknowledgements

This research was partially supported by UP Chemical and Korea Sanhak Foundation in 2012 and

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mainly supported by the Global Frontier R&D Program through the Global Frontier Hybrid Interface Materials (GFHIM) of the National Research Foundation of Korea (NRF) funded by the Ministry of

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Science, ICT & Future Planning (2013M3A6B1078870).

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Figure Captions

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Figure 1. ALD indium oxide growth rate as a function of (a) precursor temperature and (b) substrate temperature.

a function of growth temperature.

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Figure 2. (a) Resistivity, (b) Hall mobility and (c) Carrier concentration of ALD indium oxide films as

Figure 3. (a) XRD, (b) O 1s XPS, and (c) O k edge NEXAFS data of InOx film grown at different deposition temperatures using TEIn and O3.

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Figure 4. Optical bandgap values of InOx thin films grown with three different precursors and O3, with respect to deposition temperature.

Figure 5. (a) Refractive index and (b) calculated porosity of InOx films grown with three different

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precursors and O3, with respect to deposition temperature. Figure 6. Optical transmittance of InOx grown with TEIn and O3 at 50 ~ 250 °C after correcting the

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glass substrate transmittance.

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Table 1. Resistivity, Hall mobility, carrier concentration and optical bandgap values for ALD indium

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oxide films grown using three kind of precursors at 50oC ~ 250oC.

Film properties of ALD Indium Oxide (INCA/DADI/TEIn) Resistivity (Ωcm)

Hall mobility (cm2/V s)

Carrier Concentration (cm-3)

Optical bandgap (eV)

50 oC

N/D

N/D

N/D

(4.46) / (4.49) / (4.44)

100 oC

(1.13× ×10-2 ) / (2.82× ×10-1 ) / (2.00× ×10-3)

(0.32) / (11.19) / (3.95)

(1.73× ×1021 ) / (2.99× ×1018 ) / (7.99× ×1020)

(4.10) / (4.20) / (3.94)

150 oC

(5.29× ×10-4 ) / (1.06× ×10-3 ) / (3.74× ×10-4)

(4.65) / (8.16) / (13.64)

(3.12× ×1021 ) / (7.20× ×1020) / (1.23× ×1021)

(3.87) / (3.92) / (3.76)

200 C

(4.05× ×10-4 ) / (7.76× ×10-4 ) / (8.58× ×10-5)

(1.97) / (16.82) / (30.23)

(7.91× ×1021) / (4.76× ×1020 ) / (2.53× ×1021)

(3.86) / (3.75) / (3.80)

250 oC

(2.21× ×10-4 ) / (3.45× ×10-4 ) / (4.71× ×10-4)

(8.60) / (29.18) / (48.71)

(3.29× ×1021 ) / (6.21× ×1020 ) / (2.72× ×1020)

(3.90) / (3.77) / (3.83)

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Growth Temp.

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[22] J. A. Libera, J. N. Hryn, J. W. Elam, Indium Oxide Atomic Layer Deposition Facilitated by the

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Synergy between Oxygen and Water. Chem. Mater. 23 (2011) 2150-2158.

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[23] J. W. Elam, D. A. Baker, A. B. F. Martinson, M. J. Pellin, J. T. Hupp, Atomic Layer Deposition of Indium Tin Oxide Thin Films Using Nonhalogenated Precursors. J. Phys. Chem C 112 (2008) 1938-1945.

[24] Y. Wu, S. E. Potts, P. M. Hermkens, H. C. M. Knoops, F. Roozeboom, W. M. M. Kessels, Enhanced

Doping

Efficiency

of

Al-Doped

ZnO

by

Atomic

Layer

Deposition

Using

Dimethylaluminum Isopropoxide as an Alternative Aluminum Precursor. Chem. Mater. 25 (2013) 4619-4622

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ACCEPTED MANUSCRIPT [25] W. J. Maeng, D. W. Choi, K. B. Chung, W. Koh, G. Y. Kim, S. Y. Choi, J. S. Park, Highly Conducting, Transparent, and Flexible Indium Oxide Thin Film Prepared by Atomic Layer Deposition Using a New Liquid Precursor Et2InN(SiMe3)2, ACS Appl. Mater. Interfaces 6 (2014)

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17481-17488. [26] K. Kato, H. Omoto, T. Tomioka, A. Takamatsu, Changes in electrical and structural properties of indium oxide thin films through post-deposition annealing, Thin Solid Films 520 (2011) 110-116

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[27] T. Y. Chou, Y. Chi, S. F. Huang, C. S. Liu, A. J. Carty, L. Scoles, K. A. Udachin, Fluorinated Aminoalkoxide and Ketoiminate Indium Complexes as MOCVD Precursors for In2O3 Thin Film

M AN U

Deposition. Inorg. Chem. 42 (2003) 6041-6049.

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[30] T. Tomita, K. Yamashita, Y. Hayafuji, H. Adachi, The origin of n-type conductivity in undoped In2O3. Appl. Phys. Lett. 87 (2005) 051911 [31] C. Donley, D. Dunphy, D. Paine, C. Carter, K. Nebesny, P, Lee, D. Alloway, N. R. Armstrong,

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Characterization of Indium-Tin Oxide Interfaces Using X-ray Photoelectron Spectroscopy and Redox Processes of a Chemisorbed Probe Molecule: Effect of Surface Pretreatment Conditions, Langmuir 18

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[32] W. J. Maeng, H. Kim. Thermal and Plasma-Enhanced ALD of Ta and Ti Oxide Thin Films from Alkylamide Precursors. Electrochemical and Solid-State Letters 9 (2006) G191 [33] W. J. Maeng, S. J. Kim, J. S. Park, K. B. Chung, H. Kim, Low temperature atomic layer deposited Al-doped ZnO thin films and associated semiconducting properties. J. Vac. Sci. Tchnol., B 30 (2012) 031210.

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ACCEPTED MANUSCRIPT [34] D. F. Groot, M. Grioni, J. Fuggle, J. Ghijsen, G. Sawatzky, H. Petersen, Oxygen 1s x-rayabsorption edges of transition-metal oxides. Phys. Review. B 40 (1989) 5715-5723 [35] A. Walsh, D. J. L. F. Silva, S. H. Wei, C. Körber, A. Klein, L. F. J. Piper, A. DeMasi, K. E.

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Smith, G. Panaccione, P. Torelli, D. J. Payne, A. Bourlange, R. G. Egdell, Nature of the Band Gap of In2O3 Revealed by First-Principles Calculations and X-Ray Spectroscopy. Phys. Rev. Lett. 100 (2008) 167402

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[36] S. T. Tan, B. J. Chen, X. W. Sun, W. J. Fan, H. S. Kwok, X. H. Zhang, S. J. Chua, Blueshift of optical band gap in ZnO thin films grown by metal-organic chemical-vapor deposition. J. Appl. Phys

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(2013) 2240-2243.

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1.50

(a) ALD InOx o

1.25

Growth rate (A/cycle)

Tsub: 200 C

0.6

0.4 30

40

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0.8

50

o

Precursor temperature ( C)

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Growth rate (A/cycle)

1.0

Fig 1

(b) ALD InOx

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INCA DADI TEIn

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60

INCA DADI TEIn

1.00

0.75

0.50 Process window

0.25

0

50

100 150 200 o Growth temperature ( C)

250

INCA DADI TEIn

40

-2

10

-3

10

20

-4

10

100

150

200

0

250

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2

10

100

150

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200

250

Growth temperature (oC)

Growth temperature (oC)

10

(c)

22

10

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Hall mobility (cm /Vsec)

(b)

-3

INCA DADI TEIn

-1

Resistivity (Ohm.cm)

23

60

(a)

Carrier concentration (cm )

0

10

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10

20

10

19

10

INCA DADI TEIn

18

10

17

10

100

150

200

250

Growth temperature (oC)

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(b) O 1s InOx from TEIn and O3

(a) InOx from TEIn and O3

In-OH (531.3 eV)

(440)

o

(622)

250 C o

200 C o

150 C o

100 C o

30

40

50

60

70

2theta (degree)

80

528

o

150 C o

100 C o

529

530

In5sp

AC C Fig 3

o

250 C

In 5p

EP

TEY (arb. unit)

(c) O-K InOx from TEIn and O3

520

50 C

531

Binding Energy (eV)

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20

o

200 C

In2O3 (529.5 eV)

50 C

o

200 C o

150 C o

100 C o 50 C

530

540

550

560

Binding Energy (eV)

o

250 C

SC

(400) (431)

Intensity (a.u.)

(211)

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Intensity (a.u.)

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570

532

533

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4.75

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4.25 4.00 3.75 3.50

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Optical bandgap (eV)

4.50

INCA DADI TEIn

3.25

50

AC C

EP

3.00

Fig 4

100

150

200 o

Growth temperature ( C)

250

100

2.2 (a)

2.0

1.8

INCA DADI TEIn

1.6

50

100

150

200

o

EP

Growth temperature ( C)

Fig 5

250

TE D

0.0

INCA DADI TEIn

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Porosity (%)

80

AC C

Refractive index

Ideal In2O3

(b)

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0

50

100

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250 o

Growth temperature ( C)

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80 60 40

o

InOx 100 C o

InOx 150 C

20 0

o

InOx 200 C

400

500

o

InOx 250 C

600

AC C

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Wavelength (nm)

Fig 6

o

InOx 50 C

TE D

Transmittance (%)

100

700

800

ACCEPTED MANUSCRIPT Journal of Alloys and Compounds Submitted Title: “Indium oxide thin film prepared by low temperature atomic layer deposition using liquid precursors and ozone oxidant”

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Research Highlights

 InOx thin films were deposited by ALD at extremely low deposition temperatures below 100 °C.

 InOx films exhibit relatively low electrical resistivity below 10-3 Ωcm at temperatures above 150 °C.

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 Ozone stimulate the chemical reactions to yield dense indium oxide films at low temperatures.

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(a) Precursor 1 : diethyl[1,1,1-trimethyl-N-(trimethylsilyl)silanaminato]-Indium

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(b) Precursor 2 :[3-(dimethylamino-kN)propyl-kC]dimethyl-Indium

(c) Precursor 3 : Triethyl-indium

Supporting information 1. Molecular structure of In precursors. (a) diethyl[1,1,1trimethyl-N-trimethylsilyl)silanaminato]-Indium (b) [3-(dimethylamino-kN)propylkC]dimethyl-Indium (c) Triethyl-indium

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Supporting information 2. Thermogravimetry and differential scanning calorimetry of (a) ~(c) Indium precursors

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o

(a) pre-1

In2O3 50 C o

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In2O3 100 C

(222)

Intensity (arb. unit)

o

In2O3 150 C (211)

o

(431) (440)

(622)

In2O3 200 C o

In2O3 250 C

20

30

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(400)

40

50

60

70

80

2theta (degree)

(b) DADI

o

In2O3 100 C

TE D

o

(211)

(431) (440)

(400)

o

In2O3 150 C In2O3 200 C

(622)

o

In2O3 250 C

AC C

EP

Intensity (arb. unit)

(222)

o

In2O3 50 C

20

30

40

50

60

70

80

2theta (degree)

Supporting information 3. XRD patterns of ALD In2O3 films deposited on silicon substrates with different growth temperature using (a) diethyl[1,1,1-trimethyl-Ntrimethylsilyl)silanaminato]-Indium (b) [3-(dimethylamino-kN)propyl-kC]dimethylIndium precursor