Atomic Layer Deposition of Indium Gallium Oxide Thin Film for Thin

Indium gallium oxide (IGO) thin films were deposited via atomic layer deposition (ALD) ... Thus, ALD-IGO could be employed to fabricate active layers ...
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Atomic Layer Deposition of an Indium Gallium Oxide Thin Film for Thin-Film Transistor Applications Jiazhen Sheng,† Eun Jung Park,‡ Bonggeun Shong,*,‡ and Jin-Seong Park*,† †

Division of Materials Science and Engineering, Hanyang University, Seoul 04763, Korea Department of Chemistry, Chungnam National University, Daejeon 34134, Korea

‡

S Supporting Information *

ABSTRACT: Indium gallium oxide (IGO) thin films were deposited via atomic layer deposition (ALD) using [1,1,1-trimethyl-N-(trimethylsilyl)silanaminato]indium (InCA-1) and trimethylgallium (TMGa) as indium and gallium precursors, respectively, and hydrogen peroxide as the reactant. To clearly understand the mechanism of multicomponent ALD growth of oxide semiconductor materials, several variations in the precursor−reactant deposition cycles were evaluated. Gallium could be doped into the oxide film at 200 °C when accompanied by an InCA-1 pulse, and no growth of gallium oxide was observed without the simultaneous deposition of indium oxide. Density functional theory calculations for the initial adsorption of the precursors revealed that chemisorption of TMGa was kinetically hindered on hydroxylated SiOx but was spontaneous on a hydroxylated InOx surface. Moreover, the atomic composition and electrical characteristics, such as carrier concentration and resistivity, of the ALD-IGO film were controllable by adjusting the deposition supercycles, composed of InO and GaO subcycles. Thus, ALD-IGO could be employed to fabricate active layers for thin-film transistors to realize an optimum mobility of 9.45 cm2/(V s), a threshold voltage of −1.57 V, and a subthreshold slope of 0.26 V/decade. KEYWORDS: surface reaction mechanism, gallium-doped indium oxide, oxide semiconductor, TFT, ALD

I. INTRODUCTION Oxide semiconductor thin-film transistors (TFTs) have been extensively researched in the display industry because of their attractive characteristics, including high performance, low processing temperature, and simple fabrication. Besides, oxide semiconductor TFTs can show outstanding performance, required for scalability, because of their high mobility and low leakage current, attributed to their wider band gap compared to that of low-temperature polycrystalline silicon or amorphous Si.1 Indium oxide (In2O3) is a well-known transparent conducting oxide material with intrinsic oxygen deficiency that endows the material with not only a high mobility but also an undesirable negative shift in the threshold voltage, caused by an unexpected increase in oxygen vacancy densities.2,3 Doping of In2O3 has been investigated for improvement of TFT performance by reducing the density of oxygen vacancies, with elements such as gallium, hafnium, and silicon,4−6 which have larger dopant−oxygen bonddissociation energy than that of In−O (346 kJ/mol).7 Ga has a large Ga−O bond-dissociation energy (374 kJ/mol)7 and an atomic size similar to that of In so that the lattice structure and the charge transport properties of InOx would be little affected upon doping.8 Thus, as Kwon et al. reported,9 gallium-doped In2O3, or indium tin zinc oxide (ITZO), can be a potential candidate material for high-performance oxide TFTs. Indeed, among the well-known indium-based active layer materials, including indium zinc oxide (IZO), indium gallium zinc oxide © 2017 American Chemical Society

(IGZO), and indium tin zinc oxide, IGO has been utilized in high-mobility backplane devices for next-generation displays, such as 4K2K liquid crystal displays and three-dimensional (3-D) displays.10 Although sputtering is most widely used for the fabrication of oxide semiconductor TFTs, it is difficult to control the elemental ratio of sputter-deposited films without transferring the target, and the presence of high-energy species during deposition can create interfacial defects, resulting in TFT performance degradation. On the other hand, oxide TFTs fabricated using atomic layer deposition (ALD) showed a performance comparable to that of the sputtered TFTs in previous reports, for example, a mobility of 20 cm2/(V s) for zinc oxide (ZnO),11 10 cm2/(V s) for IGZO,12 and 42.1 cm2/(V s) for IZO.13 Furthermore, ALD process enables uniform deposition of films with precise control of the thickness and composition over large areas. Therefore, ALD is a promising technology for oxide semiconductor TFTs for large area display devices.11,13 In addition, ALD provides great benefits for multicomponent growth of binary systems to form ternary materials, such as Al2O3/ZnO (aluminum-doped ZnO), ZnO/SnOx (zinc−tin oxide), and In2O3/ZnO (indium zinc oxide).14 Received: April 9, 2017 Accepted: June 23, 2017 Published: June 23, 2017 23934

DOI: 10.1021/acsami.7b04985 ACS Appl. Mater. Interfaces 2017, 9, 23934−23940

Research Article

ACS Applied Materials & Interfaces

Figure 1. Diagram of different ALD processes for GaO, InO, In−Ga, Ga−In, and InO−GaO sequences.

Table 1. Growth Rate and Atomic Composition of Thin Films Grown via ALD with Various Sequences (Growth Rate and Atomic Percentages Obtained via SE and AES) sequence

supercycle

growth rate (Å/cycle)

atom % C

atom % Ga

atom % In

atom % O

GaO InO In−Ga Ga−In InO−GaO

(TMGa)−H2O2 (InCA-1) −H2O2 (InCA-1)−(TMGa)−H2O2 (TMGa)−(InCA-1)−H2O2 (InCA-1)−H2O2−(TMGa)−H2O2

0.97 0.77 0.33 0.42

0.5 0.7 0.4 0.6

0 3.8 28.3 20.6

42.8 39.6 14.9 22.7

56.7 55.9 56.4 56.2

sequences, with variations in the order of metal precursors and reactant pulses, were used, as shown in Figure 1. Hall measurements (AH5TTT5; Ecopia) were carried out to determine electrical characteristics, such as resistivity, carrier concentration, and mobility. Analysis of core-level electronic states was conducted using X-ray photoelectron spectroscopy (XPS) (Theta Probe). The crystallinity of the In2O3 (bcc phase) and IGO (amorphous) thin films was examined via θ−2θ scanning using a Rigaku X-ray diffractometer with Cu Kα radiation at 1.542 Å (Figure S1). Top-gate, bottom-contact IGO TFTs were fabricated on a glass substrate. First, a 100 nm indium tin oxide source/drain and gate layer was deposited via sputtering at room temperature, on which a 100 nm Al2O3 gate insulator layer was grown at 200 °C via ALD, using trimethylaluminum and H2O. Then, an IGO active layer with a thickness of 20 nm was deposited at 200 °C using the method mentioned above. The number of InO subcycles changed from one to three. The active region was then patterned by a combination of photolithography and wet etching steps to realize a channel width (W) and length (L) of 40 and 20 μm, respectively. The TFT devices were annealed at 300 °C in an ambient atmosphere for 1 h. The device properties of TFTs were evaluated using a HP 4155A parameter analyzer in air at room temperature. DFT calculations were performed using Orca 3.0.3 software.21 Geometry optimization was carried out using the B97-D3 functional22 with def2-TZVP basis set.23 Then, the single-point energy of the optimized structures was obtained with the PWPB95-D3 double-hybrid functional24 and def2-TZVPP basis set. All calculations involved D3 atom-pairwise dispersion correction with Becke−Johnson damping.25 The Si surface with hydroxyl functionalities was modeled using a Si15H16 cluster with two dissociatively adsorbed H2O molecules;26 the hydroxyl on the InO-terminated surface was modeled with an −OH group bonded to a trivalent In of a Si15H18O2InOH cluster (Figure S2). The transition state structures were initially guessed from relaxed potential energy surface scans and confirmed after optimization to have an imaginary vibrational mode along the suggested reaction coordinate.

In previous research on ALD for TFT applications, ZnO doped with Al, Hf, or Mg was investigated, whose elemental composition could be controlled to optimize the device performance.15−17 However, the mechanisms of ALD growth for multicomponent oxides are often more complex than a simple sum of the growth metrics for constituent binary oxides.13,18,19 Therefore, current lack of understanding regarding multicomponent ALD growth for oxide semiconductor materials is limiting their applicability as the active layer of TFTs. In this study, IGO thin films were deposited via ALD. Variations in the deposition sequence were applied, wherein a reactant pulse was emitted before and after a metal precursor pulse. Gallium could be incorporated into IGO thin films at 200 °C when the trimethylgallium (TMGa) pulse was accompanied by a [1,1,1-trimethyl-N-(trimethylsilyl)silanaminato]indium (InCA-1)−H2O2 deposition sequence. Conversely, no deposition of pure gallium oxide was observed without In2 O 3 deposition. Density functional theory (DFT) calculations showed that the surface reactivity increases to favor the adsorption of TMGa upon termination of the surface with hydroxylated InOx compared with Si(100). On the basis of the controllable composition of this ternary deposition system, IGO thin films were employed as the active layer of oxide TFTs and optimized at a specific composition ratio between In and Ga. Our results revealed that IGO thin films deposited using ALD could be promising components for oxide semiconductor TFTs.

II. EXPERIMENTAL PROCEDURES IGO thin films were deposited via ALD (NCD-D100) at 200 °C, using InCA-1 as an indium precursor, TMGa as a gallium precursor, and hydrogen peroxide (30% H2O2 with 70% H2O; Sigma Aldrich) as the reactant on a Si(100) substrate with a native oxide after acetone washing. The temperature of the indium precursor was maintained at 40 °C for sufficient vapor pressure and dose, as previously reported.20 Auger electron spectroscopy (AES) (PHI 700Xi) and spectroscopic ellipsometry (SE) (Elli-SE(UV)-FM8) were carried out to analyze the thickness and chemical composition of the thin films. Five different ALD

III. RESULTS AND DISCUSSION Table 1 shows the growth rate and chemical composition of the ALD-grown IGO thin films. No growth of gallium oxide was 23935

DOI: 10.1021/acsami.7b04985 ACS Appl. Mater. Interfaces 2017, 9, 23934−23940

Research Article

ACS Applied Materials & Interfaces

Figure 2. (a−d) XPS spectra in the O 1s region and (e) Ga 3d region of ALD-IGO thin films with InO, Ga−In, Ga−In, and InO−GaO sequences; (f) areal ratios of the three O 1s peaks (Ga−O, In−O, and −OH) from different sequences.

Figure 3. DFT-calculated energy profiles of chemisorption and optimized structures (top view) of TMGa and InCA-1 on (a) a SiOx-OH surface and (b) an InOx-OH surface. Brown = In, green = Ga, yellow = Si, red = O, blue = N, and white = H.

accompanied by a drop in the film’s growth rate to 0.42 and 0.33 Å/cycle for the InO−GaO and Ga−In sequences, respectively. A similar growth behavior for an AlxSiyOz ALD using an Al(CH3)3−D2O−Si2(NHEt)6−D2O sequence was reported by Ritala et al., who focused on how the reaction mechanism affected the chemisorption of the Si2(NHEt)6 (hexakis(ethylamino)disilane) precursor.28 The oxygen-metal bonding of the thin films was analyzed via XPS, as shown in Figure 2. The chemical concentrations of Ga and In in the IGO films obtained from XPS results corroborated those obtained from AES measurements. In particular, the O 1s region was deconvoluted into subpeaks. For metal oxides, a lower binding energy at the O 1s subpeak can generally be attributed to O that is directly bonded to metal cations, whereas peaks with a higher binding energy can be assigned to OH of hydroxides.29 In

detected when the GaO sequence was applied. This result was corroborated by a previous report in which TMGa with H2O2 or H2O could not grow gallium oxide via ALD, even at a higher deposition temperature of 350 °C.27 On the other hand, varying Ga compositions were observed when InCA-1 pulse was included in the sequence. Only 3.8% of Ga was contained in the thin film following an In−Ga (TMGa pulsed immediately after InCA-1) sequence, resulting in a slight decrease in the growth rate (0.77 Å/cycle) compared to that of the pure In2O3 ALD (InO, 0.97 Å/cycle). However, when the [(InCA-1)− H2O2] and [TMGa−H2O2] cycles were alternated using an InO−GaO sequence, the concentration of Ga rose to 20.6%. By initiating a TMGa pulse immediately following the H2O2 pulse but before the InCA-1 pulse (Ga−In sequence), the Ga content reached 28.3%. This increase in the Ga concentration was 23936

DOI: 10.1021/acsami.7b04985 ACS Appl. Mater. Interfaces 2017, 9, 23934−23940

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GaO sequence, wherein TMGa is dosed on the hydroxylated InOx surface generated by [InCA-1−H2O2] pulses, can be directly related to the reactivities of the InOx surface toward TMGa and GaOx surface toward InCA-1, as described above. In this case, both the In and Ga precursors would easily adsorb on the hydroxylated surfaces prepared after each H2O2 pulse. As a result, the atomic fractions of In and Ga are similar to each other (ca. 20%). On the other hand, in the In−Ga and Ga−In sequences, there is no H2O2 pulse included between two precursor pulses. In such situations, it can be expected that much of the surface −OH reacts with the first metal pulse, leaving methylated In or Ga moieties on the surface, which are no longer reactive toward the second precursor. Only a fraction of surface hydroxyl moieties remaining after the first precursor pulse would then allow the second precursor to adsorb, depositing a smaller amount of the second precursor on the surface. As a result, the obtained films from In−Ga and Ga−In sequences are richer in In and Ga, respectively. The properties of the ALD-IGO thin films could be systematically varied by adjusting the deposition supercycles, which consisted of InO and GaO sequences. As a proof of concept, IGO films obtained from subcycles of 3InO−GaO (three InO cycles + one GaO cycle) and InO−3GaO (one InO cycle + three GaO cycle) were compared to those from InO− GaO (one InO cycle + one GaO cycle). The AES depth profiles (Figure 4) indicated a homogeneous composition of In and Ga throughout the films. The compositional and electrical properties (Table 2) of the films demonstrated the dependence of these values on the deposition sequence. For instance, an IGO thin film with a larger number of InO cycles (3InO−GaO) exhibited the highest indium content (30.9%) and carrier concentration (1.68 × 1020 cm−3), whereas a thin film deposited with a larger number of GaO cycles (InO−3GaO) had 34.9% Ga and only 5.6% In, resulting in a higher resistivity outside the Hall measurement limit. Manipulating the composition and resulting material properties of thin films by adjusting ALD supercycles can facilitate optimization of IGO thin-film properties, thereby enabling these films to be utilized as active layers for TFTs. Putatively, the atomic ratio of In to Ga is an important factor affecting the performance of IGO TFTs.32 As the carrier concentration of the ALD-deposited pure InO thin film of 8.16 × 1020 cm−3 exceeded the threshold value for TFT active layers, a GaO subcycle was added to decrease it. On the other hand, the film deposited using the InO−GaO sequence contained 20.6% Ga, yielding a carrier concentration of 8.16 × 1018 cm−3, which was too low for an active layer material. Therefore, the relative proportions of Ga and In in the IGO film were varied by increasing the number of InO subcycles during the ALD of IGO. Table 2 lists the chemical composition and hall measurement results for the IGO thin films when the number of InO subcycles increased from one to three. Consistently to the AES data in Figure 4, the proportion of In increased with the number of InO subcycles. Such compositional variation was accompanied by an increase in the carrier concentration (1.68 × 1020 cm−3) and decrease in the resistivity (1.21 × 10−3 Ω cm) for the film deposited by 3InO−GaO sequence. TFT devices with controlled In/Ga ratios were fabricated with a top-gate bottom-contact structure, as shown in Figure 5a. The performance criteria of the IGO TFT (shown in Table 3 and Figure 5b) indicated systematic dependence on the sequence of supercycles. The TFT resulting from the 3InO−GaO sequence showed enhanced performance parameters, including a negative

addition, the O 1s core-level electrons shifted according to the deposition sequence. Therefore, the metal-bound oxygen peak could be further deconvoluted into Ga−O and In−O peaks. In particular, the lower binding energy component (530.2 eV) was ascribed to free oxygen bonded to In, whereas the higher binding energy component (530.9 eV) was related to Ga−O bonds.30 Conversely, it was difficult to distinguish the Ga-bound O 1s electrons for the film resulting from the In−Ga sequence because the Ga content was only 3.8% (Table 1). Nonetheless, the Ga 3d peak (shown in Figure 2e) revealed the presence of Ga in the film. Otherwise, the relative fraction of peaks due to O−In, O− Ga, and O impurities (Figure 2f) was consistent with the AES data (Table 1). To determine the reason behind the dependence of the films’ growth behavior on the precursor exposure sequence, a potential energy diagram for the adsorption of InCA-1 and the TMGa precursors was obtained via DFT calculations (Figure 3). Two different surface hydroxyl functional groups, those bound to Si(100) and those on a trivalent indium, were considered to represent the initial adsorption environment on the silica substrate and the functionality created after an InCA−H2O2 sequence. Molecular adsorption of both TMGa and InCA-1 on a hydroxylated Si(100) surface through O-metal dative bonding was spontaneous and did not exhibit an activation barrier (Figure 3a). However, the adsorption energies of O-dative TMGa (−72.1 kJ/mol) and InCA-1 (−90.6 kJ/mol) would have resulted in lifetimes less than 1 ms at a deposition temperature of 200 °C, assuming a typical pre-exponential factor for desorption of 1013 s−1. Thus, molecularly bonded precursors would not enable the deposition of metal ions. On the other hand, removing ligands via transfer of hydrogen from the surface hydroxyl groups is irreversible and can leave metal ions deposited on the surface after the precursor pulse. Accordingly, because the removal of [Si(CH3)3]2NH from the InCA-1 precursor involves a small activation barrier of 14.5 kJ/mol, deposition of In with this precursor easily occurs. In contrast, removal of CH4 from both TMGa and InCA-1 (not shown; similar to that of TMGa) on hydroxylated Si(100) cannot proceed due to activation barriers higher than the desorption energy of the dative-bonded precursors. Therefore, whereas nucleation of In2O3 with InCA-1 is possible, TMGa cannot lead to nucleation of gallium oxide on the silica substrate by itself. On the other hand, the reactivity of the surface to TMGa increased upon deposition of In2O3. The active surface functionality after an (InCA-1)−H2O2 sequence was modeled using a hydroxylated trivalent indium on the Si(100) surface (abbreviated as InOH).31 On this surface, TMGa spontaneously decomposed into Ga(CH3)2 and CH3, with a significant adsorption energy of −285.3 kJ/mol (Figure 3b). Both the In and Ga centers became tetravalent after dissociation of Ga−C and formation of In−C bonds. No transition state with energy above that of the entrance channel could be located, despite multiple attempts, thereby suggesting kinetic viability for this process. Subsequently, ligands of the surface-adsorbed Ga(CH3)2 could either react further with the remaining surface hydroxyl to lose CH4 or be oxidized during the H2O2 pulse. Thus, TMGa could be adsorbed on a hydroxylated In2O3 surface. This result accounted for the incorporation of gallium oxide into the thin films, which was enabled by interdeposition with In2O3. The variations in the relative amount of Ga and In in IGO films according to the sequence of the precursors can be explained in light of the above-described reactivity of the surfaces toward TMGa after each ALD pulse. The film deposited with an InO− 23937

DOI: 10.1021/acsami.7b04985 ACS Appl. Mater. Interfaces 2017, 9, 23934−23940

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hysteresis of 0.63 V, and an on−off current ratio (Ion/Ioff) of 8.0 × 108. These values were also comparable to those of IGO TFTs from previous studies (for instance, μsat of 10.7 cm2/(V s) by Bae et al.;32 5.2 cm2/(V s) by Yoon et al.33). Current results indicate that composition-adjustable ALD-IGO could be a promising TFT-active-layer candidate material. Especially, doping with Ga can improve the TFT performance of IGO by reducing the number density of oxygen vacancies, such that the Ga dopant acts as a carrier suppressor that decrease the carrier concentration.9 In our experiments, as the number of InO subcycles increased, the Ga% decreased, resulting in increased oxygen vacancies and carrier concentrations. The on current showed a dramatic increment with the fraction of the InO subcycle, and the threshold voltages also showed a negative shift. The origin of the subthreshold slope is commonly ascribed to the bulk defect density of the active layer and interface trap states (Nt) between the active layer (IGO) and gate insulator layer (Al2O3). Thus, the Nt values of each TFT were calculated using the following equation ⎡ S log(e) ⎤C Nt = ⎢ − 1⎥ i ⎣ kT /q ⎦q

where S is the subthreshold slope and Ci is the gate capacitance per unit area. The calculated Nt values (Table 3) decreases with increasing In%. This reveals that the elemental composition of the active layer can be the dominant reason for different interface density states as well as the subthreshold slope, as reported by Jeong et al.34 Besides, the compositions result in a difference in the surface characteristics, such as hydrophilicity. As shown in Figure S3, higher In% thin films show smaller water contact angles, which are translated as a larger hydrophilicity, lead to relatively faster Al2O3 nucleation and denser Al2O3 gate insulator deposition over the IGO active layer, and finally affect the interfacial properties between the active layer and gate insulator layer as well. The stability of the optimized device (with IGO deposited using the 3InO−GaO supercycle) under positive bias stress (PBS) was measured (shown in Figure S4), applying VGS = 20 V for a total stress time of 3600 s. The threshold voltage showed a positive shift for about 2.25 V, with slight degradation in mobility and S.S., which is comparable to that in the previous reports (3.87 V by Rim et al.;35 1.5 V by Bae et al.32).

IV. CONCLUSIONS IGO thin films were deposited via ALD, with variations in precursor/reactant pulse sequences. By launching a reactant pulse before and after sequential metal precursor pulses, a clear understanding of the ALD growth mechanism for multicomponent oxide semiconductor materials could be obtained. Although gallium oxide alone could not be deposited via ALD, Ga could be doped into IGO at 200 °C when a Ga precursor

Figure 4. Depth profile of IGO thin films grown via ALD with different sequences: (a) 3In−Ga, (b) In−Ga, and (c) In−3Ga.

shift in the threshold voltage (Vth) to −1.57 V, a mobility (μsat) of 9.45 cm2/(V s), a subthreshold slope (S.S.) of 0.26 V/decade,

Table 2. Chemical Composition and Electrical Characteristics of 40 nm IGO Thin Films Grown via ALD with Different Sequences: InO, 3InO−GaO, 2InO−GaO, InO−GaO, and InO−3GaO sample InO 3InO−GaO 2InO−GaO InO−GaO InO−3GaO

C% 0.5 0.6 0.6 0.6 0.5

Ga% 0 11.8 18.6 20.6 34.9

In% 42.8 30.9 24.4 22.7 5.6

O%

carrier concentration (cm−3)

mobility (cm2/(V s))

resistivity (Ω cm)

56.7 56.8 56.4 56.2 59.0

8.16 × 10 1.68 × 1020 2.14 × 1019 1.62 × 1018 out of range

20.5 35.8 22.2 17.4 out of range

3.73 × 10−4 1.21 × 10−3 9.18 × 10−2 2.22 × 10−1 out of range

20

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DOI: 10.1021/acsami.7b04985 ACS Appl. Mater. Interfaces 2017, 9, 23934−23940

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Figure 5. (a) Structure diagram of a top-gate bottom-contact IGO TFT. (b) Transfer performance of the InO−GaO sequence in different InO subcycles.

Table 3. List of Key Device Parameters of an ALD-IGO TFT Fabricated with the Sequence InO−GaO in Different InO Subcycles sequence

Vth (V)

μsat (cm2/(V s))

S.S. (V/decade)

hysteresis (V)

ION/IOFF

Nt (cm−2)

InO InO−GaO 2InO−GaO 3InO−GaO

3.02 2.58 −1.57

0.17 1.21 9.45

0.42 0.30 0.26

1.24 1.24 0.63

3.2 × 106 1.8 × 108 8.0 × 108

2.1 × 1012 1.4 × 1012 1.1 × 1012

*E-mail: [email protected] (J.-S.P.).

pulse was accompanied by an InO subcycle [(InCA-1)−H2O2]. In doing so, an atomic composition of over 20% Ga could be obtained. The mechanism behind the switch in the reactivity of the Ga precursor in relation to an InO subcycle was explained via DFT calculations: the adsorption of TMGa on the hydroxylated InOx surface would be spontaneous and irreversible. Adjusting the supercycles of InO could enable control over the atomic composition and electrical characteristics of the ALD-IGO thin films. Such controllability was applied to optimize IGO active layers in TFT devices with the aim to obtain optimal performance metrics, such as a mobility of 9.45 cm2/(V s), threshold voltage of −1.57 V, and subthreshold slope of 0.26 V/ decade.

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ORCID

Bonggeun Shong: 0000-0002-5782-6300 Jin-Seong Park: 0000-0002-9070-5666 Author Contributions

J.S. and J.-S.P. designed the InGaO ALD experiments and fabricated the TFT. E.J.P. and B.S. performed DFT calculations. The manuscript was written by the contribution of all authors, who have approved the final version of the manuscript. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS J.S. and J.-S.P. were supported by Samsung Display Co., the Ministry of Trade, Industry & Energy (MOTIE; project numbers 10051403, 10052020, and 10052027), and the Korea Display Research Corporation (KDRC). E.J.P. and B.S. were partially supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (2016R1C1B2006513). The supercomputing resources, including technical support, was partially provided by the National Institute of Supercomputing and Network/Korea Institute of Science and Technology Information (KSC-2016-C1-0007).

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.7b04985. Thin films deposited by sequences InO and In−Ga showed a crystal bcc phase attributed to none or a low concentration of the Ga element, and thin films deposited by sequences Ga−In and InO−GaO were in the amorphous phase, examined via XRD (Figure S1); side view of the SiOx-OH and InOx-OH surface model clusters for DFT calculations (Figure S2); image of water droplets used to determine the change in water contact angle on an IGO thin film with different numbers of InO subcycles (Figure S3); stability of an IGO TFT (with a 3InO−GaO supercycle) under 20 V PBS over 3600 s (Figure S4) (PDF)

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REFERENCES

(1) Bak, J. Y.; Yang, S.; Ryu, H.-J.; Park, S. H. K.; Hwang, C. S.; Yoon, S. M. Negative-Bias Light Stress Instability Mechanisms of the OxideSemiconductor Thin-Film Transistors Using In−Ga-O Channel Layers Deposited With Different Oxygen Partial Pressures. IEEE Trans. Electron Devices 2014, 61, 79−86. (2) Wager, J. F.; Yeh, B.; Hoffman, R. L.; Keszler, D. A. An Amorphous Oxide Semiconductor Thin-Film Transistor Route to Oxide Electronics. Curr. Opin. Solid State Mater. Sci. 2014, 18, 53−61.

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (B.S.). 23939

DOI: 10.1021/acsami.7b04985 ACS Appl. Mater. Interfaces 2017, 9, 23934−23940

Research Article

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DOI: 10.1021/acsami.7b04985 ACS Appl. Mater. Interfaces 2017, 9, 23934−23940