Origin of Indium Diffusion in High-k Oxide HfO2 - ACS Applied

Mar 4, 2016 - Indium (In) out-diffusion through high-k oxides severely undermines the thermal reliability of the next generation device of III-V/high-...
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Origin of Indium Diffusion in High‑k Oxide HfO2 Yaoqiao Hu,† Changhong Wang,† Hong Dong,†,‡ Robert M. Wallace,‡ Kyeongjae Cho,‡ Wei-Hua Wang,*,† and Weichao Wang*,†,‡ †

Department of Electronics and Tianjin Key Laboratory of Photo-Electronic Thin Film Device and Technology, Nankai University, Tianjin 300071, China ‡ Department of Materials Science and Engineering, University of Texas at Dallas, Richardson, Texas 75080, United States S Supporting Information *

ABSTRACT: Indium (In) out-diffusion through high-k oxides severely undermines the thermal reliability of the next generation device of III-V/high-k based metal oxide semiconductor (MOS). To date, the microscopic mechanism of In diffusion is not yet fully understood. Here, we utilize angle resolved X-ray photoelectron spectroscopy (ARXPS) and density functional theory (DFT) to explore In diffusion in high-k oxide HfO2. Our ARXPS results confirm the In diffusion through as-prepared and annealed HfO2 grown on InP substrate. The theoretical results show that the In diffusion barrier is reduced to ∼0.88 eV in the presence of oxygen vacancies (VO), whereas this barrier is as high as ∼4.78 eV in pristine HfO2. Fundamentally, we found that the high feasibility of In diffusion is owing to In nonbonding with its neighboring atoms. These findings can be extended to understand the In diffusion in other materials in addition to HfO2. KEYWORDS: indium diffusion, HfO2, high-k oxides, III-V/high-k oxide interface, first-principles calculation

1. INTRODUCTION The channel material interface with the insulating gate oxide is most crucial in determining the electric performance of metal oxide semiconductor (MOS) based microelectronic devices. The traditional Si/oxide based gate stack is experiencing great challenges when the device downscales to ever-smaller dimensions, evidenced by severely poor reliability and high leakage current.1,2 The III-V/high-k oxide has been regarded as one of the promising candidates in the next generation metal oxide semiconductor field effect transistors (MOSFET) due to its higher carrier mobility and higher breakdown electric field.2−5 However, this specific interface structure is suffering from thermal stability, caused mainly by interfacial III-V elemental diffusion,6,7 especially indium (In) diffusion in the postannealing process.8 The interfacial In diffusion could further cause interfacial gap states and charge traps in oxide, severely undermining device performance. It is thus urgently important to access the mechanism of interfacial diffusion of III-V elements to provide insights into designing a high quality of III-V/high-k MOS device. Experimentally, extensive studies about In diffusion have been reported.6−9 Through low energy ion scattering spectroscopy (LEIS) and angle resolved X-ray photoelectron spectroscopy (ARXPS), Cabrera et al.6 have found that In diffused through HfO2 after postdeposition annealing (PDA) in HfO2/ In0.53Ga0.47As stacks. Dong et al.7 also observed In out-diffusion through high-k dielectric (Al2O3 and HfO2) films grown on © 2016 American Chemical Society

InP(100) by atomic layer deposition (ALD) technique. Krylov et al.10 reported that the In out-diffusion through the InGaAs/ high-k oxide is correlated with the electronic performances of device. Recently, In diffusion at TiN/HfO2 interface is quantitatively analyzed via ARXPS with an estimated energy barrier of In diffusion ∼0.78 eV based on Fick’s diffusion law ignoring transient effects.9 Theoretically, a much higher energy barrier ∼2.73 eV was obtained by density functional theory (DFT) based on a cubic pure HfO2, conflicting with experimental observations.9 In fact, intrinsic oxygen vacancy (VO) defects normally are abundant in the HfO2 even at relatively low temperature.11−16 A simulation model without considering VO is not realistic to access the In diffusion mechanism via defect complex effects. In this paper, the diffusion of indium in HfO2 without and with oxygen vacancies is thoroughly investigated by firstprinciples calculations combined with experiments in order to explore the In diffusion microscopic mechanism. The corresponding experiments provide evidence for In upward diffusion to the HfO2 layer from the InP substrate. Meanwhile, our theoretical calculations found that the interstitial In easily diffuses due to its nearly atomic character during the diffusion process in the presence of oxygen vacancies. Received: January 26, 2016 Accepted: March 4, 2016 Published: March 4, 2016 7595

DOI: 10.1021/acsami.6b01068 ACS Appl. Mater. Interfaces 2016, 8, 7595−7600

Research Article

ACS Applied Materials & Interfaces

annealing at 400 °C, the concentration of In oxide is low and increases with the XPS takeoff angle, which suggests that the In oxide is close to the InP/HfO2 interface within the detection limit of XPS. After annealing at 400 °C, the concentration of In oxide is found to increase significantly, but the peak areas maintain nearly constant with different XPS taking off angles. This implies that In has already diffused through the HfO2 layer and located near the surface. Figure 1b shows the core level spectra of In 3d for Sample B, which was (NH4)2S treated, before and after annealing at 400 °C. The intensity of In−O/ In−S state shows a significant decrease before annealing, suggesting that the (NH4)2S treatment could suppress In outdiffusion, which is generally related to an oxide “clean up” effect.29 Nevertheless, upon PDA at 400 °C, similar to Sample A, a considerable amount of diffused In is observed as well. Therefore, the S-passivation cannot completely prevent In outdiffusion in InP/HfO2 stack at high temperature. 3.2. Structural Stabilities of Indium in HfO2. The above results experimentally prove the In diffusion through HfO2. Nevertheless, the associated In diffusion paths and fundamental mechanism are still poorly understood. In the following, we will investigate In diffusion through DFT calculations. To clarify the mechanism of In diffusion, the energetically favorable configuration of In in HfO2 should be addressed at first. Generally speaking, In possibly exists in interstitial, substitutional or antisubstitutional sites in pristine HfO2. According to the crystal structure of HfO2, the interstitial positions (InI) in HfO2 is the octahedral (InI,O) site in which an In atom is surrounded by six Hf atoms (see Figure 2a). Referring to the previous reports on defects in HfO2, the VO is the dominant intrinsic defect. In addition, the substitutional sites can be Hfsite (InHf) and O-site (InO,T) where an In atom is at the tetrahedral site surrounded by four Hf atoms for the O-site substitution. The defect formation energy, Eform, is calculated according to the following formula:30

2. EXPERIMENTAL AND COMPUTATIONAL DETAILS HfO2 layers were grown on two n-type InP (100) (supplied by AXT) substrates (samples A and B). Both InP(100) samples were degreased with acetone, methanol and isopropyl alcohol sequentially for 1 min each. Sample A was only degreased, and Sample B was initially degreased and then treated by 10% (NH4)2S at room temperature for 20 min. The HfO2 films with ∼5.6 nm thickness were deposited by atomic layer deposition (ALD) with tetrakis (dimethylamido)− hafnium (TDMA-Hf) and deionized water as the precursors.17,18 ARXPS was used to characterize the In diffusion through the high k dielectrics from the HfO2/InP stack. XPS measurements were carried out equipped with a monochromatic Al Kα1 source and a seven channel hemispherical analyzer operating at pass energy of 15 eV. The scanning angles were 35°, 45°, 60°, 70° and 80° with respect to the sample surface. To correct the shifts due to surface charging or band bending, the XPS spectra were aligned with In 3d5/2 at 444.8 eV. The apparatus used in this work has been described in detail elsewhere.19 All theoretical calculations were performed by Vienna ab initio Simulation Package (VASP)20−22 based on DFT with projected augmented wave (PAW)23,24 pseudopotentials. The generalized gradient approximation (GGA)25 of Perdew−Burke−Ernzerhof (PBE)26 functional was employed to depict the exchange-correlation potential energy. The valence electron configurations of O, In and Hf are 2s22p4, 5s25p1 and 5d26s2, respectively. For all calculations, an energy cutoff of 400 eV and Gamma-centered Monkhorst−Pack scheme to produce k-point mesh were adopted. Although HfO2 has cubic, tetragonal and monoclinic phases, they all display very similar local ionic bonding, and their atomic and electronic structures are closely related.27 Because the cubic phase is the simplest one both computationally and structurally, it was thus adopted to study In diffusion throughout this paper. For geometry optimization, supercells composed of 2 × 2 × 2 unit cells were employed, with 2 × 2 × 2 kpoint mesh sampled. All the structures were relaxed using conjugate gradient (CG) method with the convergence criterion of the force exerted on each atom less than 0.01 eV/Å. The converged energy criterion is 10−5 eV in the calculation of electronic properties. To determine the diffusion barrier, the climbing image nudged elastic band (CI-NEB)28 method was used to find minimum energy pathway (MEP) with the force convergence of 0.05 eV/Å.

Eform = Edef − Eperf −

3. RESULTS AND DISCUSSION 3.1. Indium Diffusion in Experiment. Figure 1a shows the In 3d (including 3d5/2 and 3d3/2) XPS core level spectra of InP/HfO2 system at scanning angles of 35°, 45°, 60°, 70° and 80° before and after annealing at 400 °C from sample A. Before

∑ ni ·μi

(1)

Where Edef is the energy of the supercell with defects, Eperf is the energy of the perfect supercell without any defects, ni indicates the number of the ith-atoms that have been added into (n > 0) or removed from (n < 0) the supercell and μi is the chemical potential of defective atoms. From the formation energies in Figure 2b, the Hf-site substitution (InHf) is the most energetically stable in most range of O chemical potential. Furthermore, the presence of VO also facilitates the substitution of Hf by In over a wide range of O chemical potential. The interstitial InI has a higher Eform, indicating the individual InI is energetically less stable. Likewise, we found that VO assists in the formation of In interstitial defect because the coexistence of the InI and VO has relatively lower formation energy compared with the single InI. From the relaxed atomic structure, the InI atom moves toward the VO site by approximately 0.7 Å when a nearest VO appears. Thus, a relatively larger In−O bond length created by the VO decreases the Eform of interstitial In. The highest Eform (>10 eV) defect configuration is the antisubstitution InO,T, which is centered at the tetrahedron and repelled by its four nearest neighboring Hf atoms. 3.3. Indium Diffusion Path and Diffusion Energy Barrier. Atomic diffusion might be involved in a nonequilibrium thermal process.31−33 In principle, all the above In relevant defects could participate in the diffusion. The

Figure 1. In 3d core level spectra at XPS scan angles of 35°, 45°, 60°, 70° and 80° from HfO2/InP system, (a) the “native” oxide sample, before and after annealing at 400 °C, (b) (NH4)2S treated (“S_InP”) before and after annealing at 400 °C. 7596

DOI: 10.1021/acsami.6b01068 ACS Appl. Mater. Interfaces 2016, 8, 7595−7600

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ACS Applied Materials & Interfaces

Figure 2. (a) Schematic configurations of various defects in the HfO2 lattice. For clarity, only one unit cell in the 2 × 2 × 2 supercell is presented. (b) Formation energies of these defects as functions of O chemical potential.

Figure 3. (a) Schematic diagrams of In diffusion pathways and the energy barrier curve of (b) O−O diffusion path (c) O−T−O diffusion path with one VO in a supercell and (d) O−T−O diffusion path with two VO in a supercell. Three snapshots representing the initial (IS), transition (TS) and final state (FS) are also included.

with much lower experimental observations (0.78 eV9) at the HfO2/InP interface. We thus consider the diffusion path with oxygen vacancy defects in HfO2. In the presence of one VO, In can diffuse between two octahedral sites through an adjacent tetrahedral site (O−T−O) with a barrier ∼1.90 eV (Figure 3c). In contrast with O−O path (Eb ∼ 4.78 eV), the indirect diffusion route of O−T−O with one VO is much more favorable. The results are qualitatively consistent with the calculation of formation energy of InI,T and InI,O (see Figure 2b). Compared to the initial state of In in pristine HfO2, the In atom deviates from its original octahedral position toward the vacancy site when a VO is included at the tetrahedral site. Meanwhile, the new initial state with one VO presence in the diffusion path results in a relatively larger In−O bond length of 2.05 Å. After several intermediate states, the In atom diffuses into the transition state at the tetrahedral site, namely the highest total energy state. At the final states, the In atom diffuses to the octahedral site again. Furthermore, the barrier reduces to 0.88 eV when two VO are included (Figure 3d), consistent with experimental reported result ∼0.78 eV.9 From above results, one can conclude that the VO facilitates the In atom diffusion from one interstitial site to the other. 3.4. Discussion. To clarify the microscopic nature through which the VO can effectively reduce the In diffusion barrier, we examine the In diffusion process in terms of In bonding and

feasibility of In diffusion is theoretically correlated with the diffusion energy barrier (Eb) between two energy minima. Hence, a thoroughly study on the energy barrier related to the In diffusion in HfO2 and the influence of VO on Eb are performed by CI-NEB calculations. Although the substitutional Hf-site is the most energetically favorable, the energy barrier is as large as ∼7.36 eV for In diffusing between two adjacent substitutional Hf-sites in the presence of VO (see Figure S1 in the Supporting Information). Therefore, it is virtually impossible for In atom to diffuse from one InHf site to another. For the interstitial In diffusion from one octahedral interstitial site to its nearest octahedral interstitial site (O−O) in the pristine HfO2, the energy barrier is found to be 4.78 eV, as displayed in Figure 3b. For the interstitial In diffusion along the O−O path, five intermediate image configurations were inserted between the initial and final configurations. At the initial stage, the In atom is surrounded by four oxygen atoms with In−O bond length of 2.18 Å. When the In atom moves to the transition state with the highest distorted site, In is repelled by its two nearest neighboring O atoms from both sides, leading to an energy increase of 4.78 eV. After the transition state, the distance between In and its nearest neighboring O atoms increases to release the stress, so that the total energy reduces. At the final state with In occupying the adjacent octahedral site, its geometrical structure is identical with the initial state. Nevertheless, this specific energy barrier conflicts 7597

DOI: 10.1021/acsami.6b01068 ACS Appl. Mater. Interfaces 2016, 8, 7595−7600

Research Article

ACS Applied Materials & Interfaces

Figure 4. Atomic trajectories of diffusing In with two diffusion pathways (a) O−O without VO, (b) O−T−O with VO.

electronic structures. In the case of In diffusion along O−O diffusion path, a very short In−O bond of 1.96 Å is formed when the diffusing In moves to the middle position of two O atoms (Figure 4a). The newly formed In−O bond length (1.96 Å) is shorter than the sum of their atomic radii (2.41 Å), which increases the difficulty for further diffusion of In. When the VO is introduced, the diffusing In (O−T−O path) can shift to open space left by the VO (Figure 4b), enlarging the distance between In and its nearest neighboring O atoms. Consequently, the In diffusion barrier is decreased by ∼2.9 eV. Fundamentally, it is significant to illustrate the VO-facilitated In diffusion mechanism in terms of the electronic structure. In Figure 5, the calculated local density of states (LDOS) of each

Table I. Bader Charge of In in IS, TS and FS without and with VO charge (e) states

without VO

with Vo

with two VO

IS TS FS

2.198 2.219 2.198

2.915 2.293 2.915

3.050 2.998 3.053

weaker interaction between them. Thus, the In exhibits atomiclike behavior especially at the transition state and it can easily diffuse through HfO2 as long as enough space provided by oxygen vacancies along its diffusion path. Our theoretical results could also explain the observed suppression of In outdiffusion in III-V/high-k stack during oxygen annealing.34 Because the concentration of VO in HfO2 may be reduced during the process of the oxygen annealing, part of In diffusion paths through VO are blocked and thus the In diffusion is suppressed. We can also understand the function of Spassivation in Sample B as follows. The decreased intensity of In−O state in S treated Sample B implies that part of In atoms may be bonded with S atoms at the InP/high-k interface. Once the In is captured at the interface, it is hard to diffuse through the HfO2 layer to the top surface. Thus, the In diffusion is suppressed before annealing. Nonetheless, the In−S bond is easily broken due to its small dissociation energy of ∼3.0 eV (In−O with ∼3.7 eV)35 upon annealing at high temperature. Consequently, the freely atomic-like In diffuses through the HfO2 layer after annealing. It is noted that our simulations assist in understanding the atomic-like In diffusion in the bulk HfO2 in the presence of VO. Experimentally, especially during the ALD process, the diffused In could be readily oxidized on the surface of HfO2, which is well consistent with our XPS observations. It is worthwhile to note that in pristine HfO2 the formation energy of In interstitial is higher than that of Hf substitutional site and thus too high to diffuse. Nevertheless, the diffusion energy barrier of the former is much smaller than that of the latter when the VO is present. During the kinetically thermal growth of III-V/HfO2, surface strain could be inevitably introduced and influence the formation energy of various point defects. For the specific InO,T defect, we applied a tensile and compressive strain on the supercell to check the variations of formation energy versus strain (see Figure S2 in the Supporting Information). We found that the tensile strain can greatly reduce the formation energy and enhance the preference of In defect in defect HfO2. Our findings could be extended to understand In diffusing in different materials, such as InGaAs nanowires, Cu(In,Ga)Se2

Figure 5. Partial density of states (PDOS) of IS, TS and FS in the (a) O−O and (b) O−T−O diffusion process with one VO and (c) O−T− O diffusion process with two VO.

image is presented. For the images in both O−O and O−T−O routes, the fully filled In-5s states are localized and located below the Fermi level (EF), displaying the character of lone pair electrons. Besides, the states around the EF are mostly contributed by In-5p orbitals and slightly mixed with O-2p orbitals, indicating a weak interaction between In-5p and O-2p states. More importantly, the evident difference appears in the transition state between O−O and O−T−O diffusions. Compared with O−O diffusion, In-5p states in O−T−O shift downward and O-2p states thus become tiny around EF with the increase of the VO amount, indicating a decreased charge transfer and the much weaker interaction between In and O atoms. Also, from the Bader charge analysis of In atom in each state with and without VO in Table I, it is found that at the transition state of O−O diffusion, about 0.8 electron transfers from In-5p orbitals to its surrounding O atoms. In contrast, when one VO is present, the charge transfer is reduced by 0.1 electron; when two VO are introduced, little charge transfer occurs between In and its nearest O atoms, implying much 7598

DOI: 10.1021/acsami.6b01068 ACS Appl. Mater. Interfaces 2016, 8, 7595−7600

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ACS Applied Materials & Interfaces thin films.36−39 As long as In prefers to stay in host materials and preserves its atomic-like behaviors, In does not form bonding and easily diffuses. In realistic InP/high-k stack, the In atomic-like environment is not fully satisfied, which explains the existence of the In−O bonding in both body and surface of HfO2 layer. Besides, during the process of In diffusion, part of atomic In might also form bonds with surrounding O atoms. On the top surface of HfO2, In concentration increases due to the atomic In out-diffusion. It is thus inevitable to form more In−O bonds, which is well consistent experimental observations. These findings shed lights on how to control In diffusion upon requirements when In based materials are integrated into various microelectronic devices. Actually, to resolve the In diffusion issue, one promising and practical route is through passivation of InP surface to enhance the thermal stability of InP/high-k interface. Once the In is tightly bonded at the interface, it is hard to diffuse through the HfO2 layer to the surface. Thus, many efforts are desired to explore other effective passivators to prevent In into high-k layer in the further investigations. The other route may be the process engineering such as oxygen annealing of III-V/high-k stacks as evidenced elsewhere.34

(TACC) for computational resources and technical support (http://www.tacc.utexas.edu).

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(1) Chau, R.; Datta, S.; Doczy, M.; Doyle, B.; Jin, B.; Kavalieros, J.; Majumdar, A.; Metz, M.; Radosavljevic, M. Benchmarking Nanotechnology for High-Performance and Low-Power Logic Transistor Applications. IEEE Trans. Nanotechnol. 2005, 4, 153−158. (2) del Alamo, J. A. Nanometre-scale Electronics with III−V Compound Semiconductors. Nature 2011, 479, 317−323. (3) Kang, Y. S.; Kim, D. K.; Kang, H. K.; Jeong, K. S.; Cho, M. H.; Ko, D. H.; Kim, H.; Seo, J. H.; Kim, D. C. Effects of Nitrogen Incorporation in HfO2 Grown on InP by Atomic Layer Deposition: An Evolution in Structural, Chemical, and Electrical Characteristics. ACS Appl. Mater. Interfaces 2014, 6, 3896−3906. (4) del Alamo J. A.;Antoniadis D.;Guo A.;Kim D.-H.; Kim T.-W.; Lin J.; Lu W.;Vardi A.; Zhao X. InGaAs MOSFETs for CMOS: Recent Advances in Process Technology. In Proceedings of the IEEE International Electron Devices Meeting, Washington DC, December 9−11, 2013; pp 2.1.1−2.1.4, DOI: 10.1109/IEDM.2013.6724541. (5) Gu J. J.; Ye P. D. III-V MOSFETs: From planar to 3D. In Proceedings of the IEEE 11th International Conference on Solid-State and Integrated Circuit Technology, Xi’an, October 29−November 1, 2012; pp 1−4, DOI: 10.1109/ICSICT.2012.6467810. (6) Cabrera, W.; Brennan, B.; Dong, H.; O’Regan, T. P.; Povey, I. M.; Monaghan, S.; O’Connor, É.; Hurley, P. K.; Wallace, R. M.; Chabal, Y. J. Diffusion of In0.53Ga0.47As Elements through Hafnium Oxide during Post Deposition Annealing. Appl. Phys. Lett. 2014, 104, 011601. (7) Dong, H.; KC, S.; Azcatl, A.; Cabrera, W.; Qin, X.; Brennan, B.; Zhernokletov, D.; Cho, K.; Wallace, R. M. In Situ Study of E-beam Al and Hf Metal Deposition on Native Oxide InP (100). J. Appl. Phys. 2013, 114, 203505. (8) Dong, H.; Cabrera, W.; Galatage, R. V.; Santosh, K. C.; Brennan, B.; Qin, X.; McDonnell, S.; Zhernokletov, D.; Hinkle, C. L.; Cho, K.; Chabal, Y. J.; Wallace, R. M. Indium Diffusion through High-k Dielectrics in High-k/InP Stacks. Appl. Phys. Lett. 2013, 103, 061601. (9) Sanchez-Martinez, A.; Ceballos-Sanchez, O.; Vazquez-Lepe, M. O.; Duong, T.; Arroyave, R.; Espinosa-Magaña, F.; Herrera-Gomez, A. Diffusion of In and Ga in TiN/HfO2/InGaAs Nanofilms. J. Appl. Phys. 2013, 114, 143504. (10) Krylov, I.; Gavrilov, A.; Eizenberg, M.; Ritter, D. Indium out Diffusion and Leakage Degradation in Metal/Al2O3/In0.53Ga0.47As Capacitors. Appl. Phys. Lett. 2013, 103, 053502. (11) Wang, S. J.; Chai, J. W.; Dong, Y. F.; Feng, Y. P.; Sutanto, N.; Pan, J. S.; Huan, A. C. H. Effect of Nitrogen Incorporation on the Electronic Structure and Thermal Stability of HfO2 Gate. Appl. Phys. Lett. 2006, 88, 192103. (12) Guha, S.; Narayanan, V. Oxygen Vacancies in High Dielectric Constant Oxide-Semiconductor Films. Phys. Rev. Lett. 2007, 98, 196101. (13) Foster, A. S.; Lopez Gejo, F.; Shluger, A. L.; Nieminen, R. M. Vacancy and Interstitial Defects in Hafnia. Phys. Rev. B: Condens. Matter Mater. Phys. 2002, 65, 174117. (14) Xiong, K.; Robertson, J. Point Defects in HfO2 High K Gate Oxide. Microelectron. Eng. 2005, 80, 408−411. (15) McIntyre, P. C. Bulk and Interfacial Oxygen Defects in HfO2 Gate Dielectric Stacks: A Critical Assessment. ECS Trans. 2007, 11 (4), 235−249. (16) Broqvist, P.; Pasquarello, A. Oxygen Vacancy in Monoclinic HfO2: A Consistent Interpretation of Trap Assisted Conduction, Direct Electron Injection, and Optical Absorption Experiments. Appl. Phys. Lett. 2006, 89, 262904. (17) Galatage, R. V.; Dong, H.; Zhernokletov, D. M.; Brennan, B.; Hinkle, C. L.; Wallace, R. M.; Vogel, E. M. Effect of Post Deposition Anneal on the Characteristics of HfO2/InP Metal-Oxide Semiconductor Capacitors. Appl. Phys. Lett. 2011, 99, 172901. (18) Galatage, R. V.; Dong, H.; Zhernokletov, D. M.; Brennan, B.; Hinkle, C. L.; Wallace, R. M.; Vogel, E. M. Electrical and Chemical

4. CONLUSIONS Indium diffusion in HfO2 has been investigated by ARXPS and DFT calculations. Clear evidence for In diffusion through HfO2 dielectric was provided by ARXPS. The DFT calculations showed that VO can facilitate the formation of In substitutional and interstitial defects in HfO2. The direct jump of interstitial In via O−O diffusion pathway has a diffusion barrier of ∼4.78 eV, which is energetically less favorable than the indirect jump O−T−O when oxygen vacancies are included. The latter has a diffusion barrier of ∼1.98 eV with one VO and ∼0.88 eV with two VO. The oxygen vacancy facilitates interstitial In diffusion, where In almost preserves its atomic character. These results will provide the fundamental understanding for the In diffusion in HfO2, other high-k oxides and further III-V/high-k device applications.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.6b01068. Details on substitutional InHf diffusion and dependence of relative energy of supercell with InO,T on lattice constants (PDF).

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AUTHOR INFORMATION

Corresponding Authors

*Email: [email protected] (W.-H. Wang). Tel.:+8622-23509930. Fax: +86-22-23509930. *Email: [email protected] (W. Wang). Tel.:+86-2223509930. Fax: +86-22-23509930. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (Grants Nos. 11104148, 11304161, 21573117 and 61504070), the 1000 Youth Talents Plan and the Fundamental Research Funds for the Central Universities. We also thank the Texas Advanced Computing Center 7599

DOI: 10.1021/acsami.6b01068 ACS Appl. Mater. Interfaces 2016, 8, 7595−7600

Research Article

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DOI: 10.1021/acsami.6b01068 ACS Appl. Mater. Interfaces 2016, 8, 7595−7600