Browsing by Author "Kim, Jiyoung"
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Item A Steep-slope Threshold Switching Selector Using Silver-doped Polycrystalline Zinc Oxide: Fabrication, Characterization, & Application for 3D X-point Memory & Neuromorphic Devices(December 2021) Sahota, Akshay; Kim, Jiyoung; Farago, Andras; Gu, Qing; Lee, Jeong-Bong; Young, Chadwin D.An assortment of emerging non-volatile memory (NVM) devices has displayed a surge of interest in being investigated for their implementation in energy-efficient bio-inspired neuromorphic computing. The intrinsic device physics of NVMs give them the capability to be employed for emulating the dynamics of a biological neuron and synapse. NVM devices are connected in a dense cross (X)-point circuit architecture thus enabling massive system-level parallelism necessary for a neural network. However, the leakage/sneak current that typically arises from neighboring unselected memory cells is considered as a stumbling block in enlarging X-point arrays. Metalfilament threshold switch has been suggested as a selector device, demonstrated on low leakage characteristics, that holds potentiality due to its straightforward metal-insulator-metal structure, superior performance, and excellent CMOS process compatibility. This dissertation demonstrates research study on the electrical and surface characterization of nano-polycrystalline silver-doped zinc oxide (ZnO) thin films for threshold switching selector device, to propose a way for amending the prevalent selector drawbacks: threshold voltage (Vth) variabilities i.e., intercell and cycle-to-cycle shifts and lousy DC cycling endurance. The current work demonstrates a novel approach to subside system variabilities by uniformly doping a crystalline selector medium i.e., ZnO with Ag metal atoms, rather than incorporating an Ag active metal layer/electrode. First, electrochemical deposition (ECD) process has been employed to slightly dope ZnO with Ag, because of its admirable dopant concentration controllability having atomic percent precision. ECD process helps in demonstrating the proof-of-concept experiment and provides an understanding of volatile switching behavior when ZnO is lightly doped with Ag. Next, “supercycle ALD” technique has been evaluated, where alternating ZnO ALD and Ag metal ALD was employed for lightly doping/delta doping ZnO with Ag. To fend off the shortcomings/drawbacks associated with both the ECD and ALD processes, RF magnetron co-sputtering process is the last fabrication method put to evaluation. Co-sputtering technique provides the wherewithal to control Ag doping levels when lightly doped composite targets (ZnO/Ag 100-x/x at. %, x=1,3,10) are employed. The switching parameters were observed to significantly improve and the trends have been explained based on surface characterizations with XPS, GIXRD, AFM, SEM, EDAX, ICP-MS, HR-TEM, and semiconductor parameter analyzer.Item Atomic Layer Deposition Application in Interconnect Technology: From Material Understanding to Area Selective Deposition(December 2021) Hwang, Su Min; Kim, Jiyoung; Kehtarnavaz, Nasser; Quevedo-Lopez, Manuel; Alavrez, Daniel; Wallace, Robert M.; Walker, Amy V.Atomic layer deposition (ALD) technique has been widely employed in the semiconductor industry. As the devices continuously scaling down to sub 3 nm, SiOx and SiNx thin films, for applications such as a spacer or an etch stopper, are expected to satisfy stringent requirements (e.g., precise thickness control, high bulk film density, high wet-etch resistance, conformality, and lowthermal budget) in the current back-end-of-line process. Besides the film qualities, challenges in the current “top-down” approach also need to be addressed to reduce the size of the devices. Moreover, the lack of a fundamental understanding of surface chemistry using in-situ characterization can further impede future interconnect technology. This dissertation focuses on the application of the ALD process for current and future interconnect technology applications. The first study is ALD of high-quality SiOx and SiNx films with lowtemperature feasibility. With the structural modification of conventional Si precursors (e.g., the addition of ligand or substitution of terminating groups), the molecular polarity of precursors is changed, resulting in the improvement of surface reactivities. By leveraging the unique structure of the Si sources, the film deposition at low temperature with enhanced film properties can be achieved. Secondly, this dissertation further identifies the correlation between the metal surface condition and physical/chemical stability of passivation materials in application to the areaselective deposition process. Using in-situ reflectance absorption infrared spectroscopy (RAIRS), X-ray photoelectron spectroscopy (XPS), and high-resolution TEM analysis, the issues arising with poor ALD selectivity are identified. After analyzing the issues, the potential solution to provide a high-quality SAM monolayer is demonstrated. Lastly, a cleaning process using a noble metal cleaning agent, in which a clean metal surface at low temperature (< 200 o C) can be achieved, is developed. The unique cleaning process could pave the way for the implementation of the consecutive organic-free area-selective-deposition process.Item Atomic-scale Characterization of Surface and Interface Dynamics in Novel Materials: Cr2Ge2Te6, NbSe2, and Strontium Barium Niobate(2021-05-01T05:00:00.000Z) Kwon, Sunah; Kim, Moon; Yang, Wei; Kim, Jiyoung; Young, Chadwin; Vandenberghe, William; Hinkle, ChristopherTransition metal dichalcogenides (TMDs) and transition metal trichalcogenides (TMT) are promising layered materials for novel electronic and optoelectronic device applications due to their fascinating electronic, optical, magnetic, and chemical properties with two dimensional (2D) atomic limits. However, their thermal stability and thermally induced defects, which are crucial for reliable operation of the devices, remain an area for further investigations. The electro-optic (EO) materials with high Pockels coefficient are also an intriguing research field for fast, small, and low power consumption electro-optical devices. Integrating the EO materials on the current silicon technologies is challenging due to demands for high crystal quality and sensitivity to orientation but highly desirable to expand their application field with compact design and low power consumption. This dissertation focuses on the thermal stability and thermal evolution studies of 𝑁𝑏𝑆𝑒2(TMD) and 𝐶𝑟2𝐺𝑒2𝑇𝑒6 (TMT) at the surface and material interface by employing in-situ scanning transmission electron microscopy (STEM) to probe the dynamics of thermal evolution and defects. The interface and surface of molecular beam epitaxial (MBE) grown strontium barium niobate on silicon with strontium titanate buffer layer is also investigated using STEM to understand the nature and growth mechanism.Item Chemical and Electrical Characterization of the HfO2/InAlAs InterfaceBrennan, Barry; Galatage, Rohit V.; Thomas, K.; Pelucchi, E.; Hurley, P. K.; Kim, Jiyoung; Hinkle, Christopher L.; Vogel, E. M.; Wallace, Robert M.InAlAs has the potential to be used as a barrier layer in buried channel quantum well field effect transistor devices due to favorable lattice-matching and carrier confinement properties with InGaAs. Field effect device structures of this nature may also require a high-k oxide deposited on the InAlAs surface to reduce leakage current. This study investigates the impact of surface preparations and atomic layer deposition of HfO2 on these surfaces using x-ray photoelectron spectroscopy to analyse the chemical interactions taking place, as well as the electrical performance of associated capacitor devices. A large concentration of As related surface features is observed at the InAlAs surface, and is attributed to a large Dit response in electrical measurements.Item Covalent Nitrogen Doping in Molecular Beam Epitaxy-Grown and Bulk WSe₂(American Institute of Physics Inc, 2018-10-22) Khosravi, Ava; Addou, Rafik; Smyth, Christopher M.; Yue, Ruoyu; Cormier, Christopher R.; Kim, Jiyoung; Hinkle, Christopher L.; Wallace, Robert M.; 0000-0002-5454-0315 (Addou, R); 0000-0003-2781-5149 (Kim, J); 0000-0001-5566-4806 (Wallace, RM); 70133685 (Kim, J); Addou, Rafik; Smyth, Christopher M.; Yue, Ruoyu; Cormier, Christopher R.; Kim, Jiyoung; Hinkle, Christopher L.; Wallace, Robert M.Covalent p-type doping of WSe₂ thin films grown by molecular beam epitaxy and WSe₂ exfoliated from bulk crystals is achieved via remote nitrogen plasma exposure. X-ray photoelectron and Raman spectroscopies indicate covalently bonded nitrogen in the WSe₂ lattice as well as tunable nitrogen concentration with N₂ plasma exposure time. Furthermore, nitrogen incorporation induces compressive strain on the WSe₂ lattice after N₂ plasma exposure. Finally, atomic force microscopy and scanning tunneling microscopy reveal that N₂ plasma treatment needs to be carefully tuned to avoid any unwanted strain or surface damage.Item A Crystalline Oxide Passivation for Al₂O₃/AlGaN/GaN(American Institute of Physics Inc.) Qin, Xiaoye; Dong, Hong; Kim, Jiyoung; Wallace, Robert M.; A-5283-2008 (Wallace, RM)In situ X-ray photoelectron spectroscopy and low energy electron diffraction are performed to study the formation of a crystalline oxide on the AlGaN surface. The oxidation of the AlGaN surface is prepared by annealing and remote N₂+O₂ plasma pretreatments resulting in a stable crystalline oxide. The impact of the oxide on the interface state density is studied by capacitance voltage (C-V) measurements. It is found that a remote plasma exposure at 550⁰ C shows the smallest frequency dispersion. Crystalline oxide formation may provide a novel passivation method for high quality AlGaN/GaN devices.Item Effect of Film Thickness on the Ferroelectric and Dielectric Properties of Low-Temperature (400 ⁰C) Hf₀.₅Zr₀.₅O₂ Films(American Institute of Physics) Kim, Si Joon; Mohan. Jaidah; Lee, Jaebeom; Lee, Joy S.; Lucero, Antonion T.; Young, Chandwin D.; Colombo, Luigi; Summerfelt, Scott R.; San, Tamer; Kim, Jiyoung; Kim, Si Joon; Mohan. Jaidah; Lee, Jaebeom; Lee, Joy S.; Lucero, Antonion T.; Young, Chandwin D.; Colombo, Luigi; Kim, JiyoungWe report on the effect of the Hf₀.₅Zr₀.₅O₂ (HZO) film thickness on the ferroelectric and dielectric properties using pulse write/read measurements. HZO films of thicknesses ranging from 5 to 20 nm were annealed at 400 ⁰C for 1min in a nitrogen ambient to be compatible with the back-end of the line thermal budget. As the HZO film thickness decreases, low-voltage operation (1.0V or less) can be achieved without the dead layer effect, although switching polarization (P_{sw}) tends to decrease due to the smaller grain size. Meanwhile, for 20-nm-thick HZO films prepared under the identical stress (similar TiN top electrode thickness and thermal budget), the P_{sw} and dielectric constant are reduced because of additional monoclinic phase formation.Item Engineering The Palladium-WSe₂ Interface Chemistry for Field Effect Transistors with High-Performance Hole Contacts(Amer Chemical Soc, 2018-12-07) Smyth, Christopher M.; Walsh, Lee A.; Bolshakov, Pavel; Catalano, Massimo; Addou, Rafik; Wang, Luhua; Kim, Jiyoung; Kim, Moon J.; Young, Chadwin D.; Hinkle, Christopher L.; Wallace, Robert M.; 0000-0001-5566-4806 (Wallace, RM); 0000-0003-0690-7423 (Young, CD); 0000-0003-2781-5149 (Kim, J); 0000-0002-6688-8626 (Walsh, LA); 0000-0002-5485-6600 (Hinkle, CD); 0000-0002-5454-0315 (Addou, R); 70133685 (Kim, J); Smyth, Christopher M.; Walsh, Lee A.; Bolshakov, Pavel; Catalano, Massimo; Addou, Rafik; Wang, Luhua; Kim, Jiyoung; Kim, Moon J.; Young, Chadwin D.; Hinkle, Christopher L.; Wallace, Robert M.Palladium has been widely employed as a hole contact to WSe₂ and has enabled, at times, the highest WSe₂ transistor performance. However, there are orders of magnitude variation across the literature in Pd-WSe₂ contact resistance and I-ON/I-OFF ratios with no true understanding of how to consistently achieve high-performance contacts. In this work, WSe₂ transistors with impressive I-ON/I-OFF ratios of 10(6) and Pd-WSe₂ Schottky diodes with near-zero variability are demonstrated utilizing Ohmic-like Pd contacts through deliberate control of the interface chemistry. The increased concentration of a PdSeₓ intermetallic is correlated with an Ohmic band alignment and concomitant defect passivation, which further reduces the contact resistance, variability, and barrier height inhomogeneity. The lowest contact resistance occurs when a 60 min post-metallization anneal at 400 degrees C in forming gas (FG) is performed. X-ray photoelectron spectroscopy indicates this FG anneal produces 3x the concentration of PdSeₓ and an Ohmic band alignment, in contrast to that detected after annealing in ultrahigh vacuum, during which a 0.2 eV hole Schottky barrier forms. Raman spectroscopy and scanning transmission electron microscopy highlight the necessity of the fabrication step to achieve high-performance contacts as no PdSeₓ forms, and WSe₂ is unperturbed by room temperature Pd deposition. However, at least one WSe₂ layer is consumed by the necessary interface reactions that form PdSeₓ requiring strategic exploitation of a sacrificial WSe₂ layer during device fabrication. The interface chemistry and structural properties are correlated with Pd-WSe₂ diode and transistor performance, and the recommended processing steps are provided to enable reliable high-performance contact formation.Item Evaluation and Integration of Graphene Field Effect Devices(2020-04-22) Ravichandran, Arul Vigneswar; Kim, Jiyoung; Young, Chadwin D.Graphene field effect devices have potential applications in emerging analogue and sensing technology. However, to use them in end applications, evaluation of such devices in terms of mobility, contact resistivity, and sheet resistance is pivotal. These fundamental parameters will dictate and enable the designing of futuristic graphene-based devices. Finally, these devices should be packaged depending on the final application or for further evaluation in an industrial perspective. This work explores the evaluation of graphene field effect devices that has been fabricated using Chemical Vapor Deposition (CVD) graphene source with optimization of the device fabrication process flows on 90 nmSiO2 using materials characterization techniques such as Raman spectroscopy, Atomic Force Microscopy, X-ray photoelectron spectroscopy, and spectroscopic ellipsometry. The issues arising with dual-gated graphene transistor is identified and one of the potential solutions to downscale the back-gate dielectric is demonstrated. Critical device parameters like mobility, contact resistivity of graphene devices are evaluated and final integration of such devices at a package level is demonstrated. For commercialization of graphene nanoelectronics, heterogeneous integration of graphene devices on commercially available CMOS substrate is the key and process flow for such devices is demonstrated. Additionally, a novel device architecture to electrically dope graphene in the contact regions is identified and this could pave way for implementation of futuristic graphene devices with tailored device properties.Item Ferroelectric HfxZr1-xO2 for Next Generation Non-volatile Memory Applications and Its Reliability(December 2021) Mohan, Jaidah; Kim, Jiyoung; Harabagiu, Sanda; Wallace, Robert M; Summerfelt, Scott R; Young, Chadwin D; Gnade, BruceTo keep up with the increasing memory demands, developing memories with higher densities, speed and energy efficiency is necessary at different levels of the memory hierarchy. Ferroelectric materials have been considered alternative memory components; however, the conventional perovskite-based ferroelectric materials pose several challenges due to CMOS integration, high thermal budget, and scaling to sub 70 nm thicknesses. In this regard, the discovery of ferroelectricity in doped HfO2 thin films was revolutionary as HfO2 is already employed in front end CMOS as a high-k dielectric material for scaled thicknesses (<10 nm) . Additionally, doping HfO2 films with ZrO2, i.e., Hf0.5Zr0.5O2 (HZO) showed stable ferroelectric phase crystallization at back-end of line compatible temperatures (<450 °C). This dissertation addresses some critical issues on the stress-induced crystallization of the ferroelectric phase in HZO films, the reliability properties of metal-ferroelectric-metal (MFM) structures, scaling ferroelectric HZO films on silicon substrates, and their reliability. First, the driving forces for the crystallization of pure ferroelectric phase in HZO thin films were addressed and the role of the TiN top electrode in phase crystallization at low process temperatures (400 °C) is studied. Then, the reliability of 10 nm thick HZO films was studied, and the various ferroelectric device reliability properties and mechanisms were evaluated for metal-ferroelectricmetal structures. Finally, the ferroelectric HZO films were integrated directly on silicon for FeFET applications and the effect of ferroelectric device reliability based on scaling HZO films on silicon structures was studied.Item Ferroelectric Hf₀․₅Zr₀․₅O₂ Thin Films: A Review of Recent Advances(Springer, 2018-09-28) Kim, Si Joon; Mohan, Jaidah; Summerfelt, Scott R.; Kim, Jiyoung; 0000-0003-2781-5149 (Kim, J); 70133685 (Kim, J); Mohan, Jaidah; Kim, JiyoungFerroelectricity in HfO₂-based materials, especially Hf₀․₅Zr₀․₅O₂ (HZO), is today one of the most attractive topics because of its wide range of applications in ferroelectric random-access memory, ferroelectric field-effect transistors, ferroelectric tunneling junctions, steep-slope devices, and synaptic devices. The main reason for this increasing interest is that, when compared with conventional ferroelectric materials, HZO is compatible with complementary metal-oxide-semiconductor flow [even back-end of the line thermal budget] and can exhibit robust ferroelectricity even at extremely thin (<10nm) thicknesses. In this report, recent advances in the ferroelectric properties of HZO thin films since the first report in 2011, including doping effects, mechanical stress effects, interface effects, and ferroelectric film thickness effects, are comprehensively reviewed.Item Ferroelectric TiN/Hf₀.₅Zr₀.₅O₂/Tin Capacitors with Low-Voltage Operation and High Reliability for Next-Generation FRAM Applications(Institute of Electrical and Electronics Engineers Inc.) Kim, Si Joon; Mohan, Jaidah; Young, Chadwin D.; Colombo, Luigi; Kim, Jiyoung; Summerfelt, S. R.; San, T.; 0000-0003-0690-7423 (Young, CD); 0000-0003-2781-5149 (Kim, J); 70133685 (Kim, J); Kim, Si Joon; Mohan, Jaidah; Young, Chadwin D.; Colombo, Luigi; Kim, JiyoungIn this study, we investigated the ferroelectric properties of Hf₀.₅Zr₀.₅O₂ (HZO) thin films with different thicknesses (5-20 nm) deposited by atomic layer deposition for the development of future ferroelectric random access memory cells. HZO-based capacitors with a thickness of 5 nm exhibited a switching polarization of ~13 μC/cm² and a ferroelectric saturation voltage of 1.0 V as extracted from the pulse write/read measurements. Furthermore, we performed fatigue measurements and we found no degradation up to 10¹⁰ switching cycles at 1.2 V.Item From Material Understanding to Volatile Threshold Switches Using Crystalline Zinc Oxide: Selector Device for X-point Memory Application(2020-04-22) Kim, Harrison; Kim, Jiyoung; Walker, Amy V.A cross-point array is considered a promising architecture that accelerates neuro-inspired machine learning algorithms. Leakage current arising from neighboring un/half-selected memory cells is the main source of power dissipation in the cross-point array and it also increases the read/write disturbance when not properly suppressed. Leakage current is considered as one of the main hurdles that must be overcome to increase the density of cross-point memory arrays, where highdensity is essentially required to achieve the neuromorphic network. A filament-type selector has been suggested as a threshold switching selector that holds the potential for applications in largescale integration that reduces read/write disturbance, and power consumption because of its ultralow leakage current compared to other types of threshold switching selectors. This dissertation focuses on the characterization of the surface and interface of crystalline zinc oxide (ZnO) switching layers, to propose a way to mend the common drawbacks associated with the filament-type threshold switching selectors; threshold voltage variability and poor cycling endurance. Initially, a variety of materials characterization techniques, such as Raman, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscope (SEM), four-point probe, Hall measurement, including in-situ electrical monitoring using UHV cluster tool, have been employed to understand the material properties of atomic layer deposited (ALD) crystalline ZnO. Afterward, a technique so-called “super-cycle ALD”, alternating ZnO ALD and Ag metal ALD, to lightly dope ZnO with Ag, has been proposed. Switching parameters are evaluated, however, unstable volatility of silver precursor made it nearly impossible to reproduce the results using ALD. Thus, to lightly dope ZnO with silver, the electrochemical deposition (ECD) process is then adopted as it is highly beneficial in controlling the doping concentration in ZnO with atomic percent precision. ECD process helps in the understanding of volatile switching behavior in lightly doped ZnO with Ag, however, inherently has difficulties in controlling the morphology and thickness. To circumvent the shortcomings associated with both processes, the co-sputtering process (with two different targets sputtered in synchronized phases) has been employed. The significantly improved switching parameters are explained based on Raman, XPS, XRD, AFM, HR-TEM, and semiconductor parameter analyzer.Item High Mobility III-V Semiconductor Devices with Gate Dielectrics and Passivation Layers Grown by Atomic Layer Deposition(2018-05) Meng, Xin; 0000-0003-0933-6419 (Meng, X); Kim, JiyoungThis dissertation focuses on the applications of atomic layer deposition (ALD) to high mobility III-V semiconductor devices. The first study is an in situ ALD-based interface passivation technique using ALD diethylzinc (DEZ) treatment on n-type and p-type In₀․₅₃Ga₀․₄₇As substrate. The capacitance-voltage (C-V) characteristics of metal-oxide-semiconductor capacitors (MOSCAPs) were studied for a variety of ALD DEZ treatment cycles, different measurement temperatures, and different thickness of ALD-grown high-k gate insulators. The reasons for the presence of inversion-like C-V characteristics shown on n-type substrates are discussed. In addition to ALD DEZ passivation, two alternative ALD-based interface passivation techniques were studied. Furthermore, inversion-type enhancement-mode n-channel and p-channel In₀․₅₃Ga₀․₄₇As metal-oxide-semiconductor field-effect transistors (MOSFETs) were demonstrated using in situ ALD DEZ-based interface passivation techniques. The second part of this dissertation is the fabrication and characterization of AlGaN/GaN MIS-HEMTs. Silicon nitride (SiNₓ), grown by low-temperature hollow cathode plasma-enhanced ALD (PEALD), served as a gate dielectric and a surface passivation layer for MIS-HEMTs. Extensive characterization of the devices was done by high-resolution transmission electron microscopy (HRTEM), current-voltage (I-V) measurement, C-V measurement, gate bias stress measurement, and pulsed I-V measurement. The SiNₓ/GaN MIS-HEMTs not only showed a crystalline interfacial layer in the HRTEM images of gate stack, but also demonstrated excellent threshold voltage stability and a mitigated current collapse. Clearly, the effective passivation of surface/interface defects (e.g., nitrogen vacancies and dangling bonds) by the crystalline interfacial layer and the low bulk trap density of PEALD SiNx are highly beneficial to the reliability of GaN devices. The last part of this dissertation mainly focuses on the electrical characteristics of AlGaN/GaN heterostructure with ALD-grown epitaxial ZnO cap layer. Theoretically, it was predicted that the piezoelectric polarization of epitaxial ZnO cap layer should have a direction opposite to that in the underlying AlGaN/GaN substrate. As a result, resembling the effect of an InGaN cap layer, a ZnO cap layer may deplete the two-dimensional electron gas (2DEG) near the AlGaN/GaN interface. Experimentally, HRTEM confirmed the epitaxial growth of single-crystalline ZnO cap layer on AlGaN/GaN heterostructure by thermal ALD at 300 °C. The Ids-Vg transfer curve and C-V curve showed a significant positive shift (~1 V) for devices with an O₃-based epitaxial ZnO cap layer, compared to those of Schottky gate devices and devices with a highly conductive H₂O-based epitaxial ZnO cap layer.Item High-κ Dielectric on ReS₂: In-Situ Thermal Versus Plasma-Enhanced Atomic Layer Deposition of Al₂O₃(MDPI AG, 2019-03-30) Khosravi, Ava; Addou, Rafik; Catalano, Massimo; Kim, Jiyoung; Wallace, Robert M.; 0000-0003-2781-5149 (Kim, J); 0000-0001-5566-4806 (Wallace, RM); 0000-0001-9901-9809 (Khosravi, A); 0000-0002-5454-0315 (Addou, R); 70133685 (Kim, J); Khosravi, Ava; Addou, Rafik; Catalano, Massimo; Kim, Jiyoung; Wallace, Robert M.We report an excellent growth behavior of a high-κ dielectric on ReS₂ , a two-dimensional (2D) transition metal dichalcogenide (TMD). The atomic layer deposition (ALD) of an Al₂O₃ thin film on the UV-Ozone pretreated surface of ReS₂ yields a pinhole free and conformal growth. In-situ half-cycle X-ray photoelectron spectroscopy (XPS) was used to monitor the interfacial chemistry and ex-situ atomic force microscopy (AFM) was used to evaluate the surface morphology. A significant enhancement in the uniformity of the Al₂O₃ thin film was deposited via plasma-enhanced atomic layer deposition (PEALD), while pinhole free Al₂O₃ was achieved using a UV-Ozone pretreatment. The ReS₂ substrate stays intact during all different experiments and processes without any formation of the Re oxide. This work demonstrates that a combination of the ALD process and the formation of weak S-O bonds presents an effective route for a uniform and conformal high-κ dielectric for advanced devices based on 2D materials. © 2019 by the authors.Item Hydroquinone-ZnO Nano-Laminate Deposited by Molecular-Atomic Layer Deposition(American Institute of Physics Inc) Huang, Jie; Lucero, Antonio T.; Cheng, Lanxia; Hwang, Hyeon Jun; Ha, M. -W; Kim, Jiyoung; 70133685 (Kim, J)In this study, we have deposited organic-inorganic hybrid semiconducting hydroquinone (HQ)/zinc oxide (ZnO) superlattices using molecular-atomic layer deposition, which enables accurate control of film thickness, excellent uniformity, and sharp interfaces at a low deposition temperature (150 °C). Self-limiting growth of organic layers is observed for the HQ precursor on ZnO surface. Nano-laminates were prepared by varying the number of HQ to ZnO cycles in order to investigate the physical and electrical effects of different HQ to ZnO ratios. It is indicated that the addition of HQ layer results in enhanced mobility and reduced carrier concentration. The highest Hall mobility of approximately 2.3 cm²/V·s and the lowest n-type carrier concentration of approximately 1.0 × 10¹⁸/cm³ were achieved with the organic-inorganic superlattice deposited with a ratio of 10 ZnO cycles to 1 HQ cycle. This study offers an approach to tune the electrical transport characteristics of ALD ZnO matrix thin films using an organic dopant. Moreover, with organic embedment, this nano-laminate material may be useful for flexible electronics.Item Impurity and Silicate Formation Dependence on O₃ Pulse Time and the Growth Temperature in Atomic-Layer-Deposited La₂O₃ Thin Films(American Institute of Physics Inc, 2018-09-24) Park, Tae Joo; Byun, Young-Byun; Wallace, Robert M.; Kim, Jiyoung; Park, Tae Joo; Byun, Young-Byun; Wallace, Robert M.; Kim, JiyoungAtomic-layer-deposited La₂O₃ films were grown on Si with different O₃ pulse times and growth temperatures. The interfacial reactions and impurity behaviors were observed using in situ X-ray photoelectron spectroscopy. Longer pulse time of O₃ formed the solid SiO₂ interfacial barrier layer, which suppressed La-silicate formation. Meanwhile, the carboxyl compound acting as an impurity phase was replaced with LaCO₃ on increasing the O₃ pulse time due to further oxidation and reaction of La. Higher growth temperatures enhanced La-silicate formation by mixed diffusion of Si and La₂O₃, during which most of the La₂O₃ phase was consumed at 400 °C. C and N impurities decreased with increasing growth temperature and completely disappear at 400 °C.Item In situ atomic layer deposition half cycle study of Al2O 3 growth on AlGaN(American Institute of Physics, 2012-11-10) Brennan, Barry; Qin, Xiaoye; Dong, Hong; Kim, Jiyoung; Wallace, Robert M.; 70133685 (Kim, J)Use the DOI address to see the article abstract. A subscription or fee may be necessary to view the article.Item In Situ Study of the Role of Substrate Temperature during Atomic Layer Deposition of HfO2 on InP(2013-10-16) Dong, Hong; Santosh, KC; Qin, Xiaoye; Brennan, Barry; McDonnell, Steven; Zhernokletov, Dmitry; Hinkle, Christopher L.; Kim, Jiyoung; Cho, Kyeongjie; Wallace, Robert M.; 70133685 (Kim, J)The dependence of the "self cleaning" effect of the substrate oxides on substrate temperature during atomic layer deposition (ALD) of HfO₂ on various chemically treated and native oxide InP (100) substrates is investigated using in situ X-ray photoelectron spectroscopy. The removal of In-oxide is found to be more efficient at higher ALD temperatures. The P oxidation states on native oxide and acid etched samples are seen to change, with the total P-oxide concentration remaining constant, after 10 cycles of ALD HfO₂ at different temperatures. An (NH₄)₂ S treatment is seen to effectively remove native oxides and passivate the InP surfaces independent of substrate temperature studied (200°C, 250°C and 300°C) before and after the ALD process. Density functional theory modeling provides insight into the mechanism of the changes in the P-oxide chemical states.Item Investigation of Arsenic and Antimony Capping Layers, and Half Cycle Reactions During Atomic Layer Deposition of Al₂O₃ on GaSb(100)Zhernokletov, Dmitry M.; Dong, Hong; Brennan, Barry; Kim, Jiyoung; Wallace, Robert M.; Yakimov, M.; Tokranov, V.; Oktyabrsky, S.; 70133685 (Kim, J)In-situ monochromatic x-ray photoelectron spectroscopy, low energy electron diffraction, ion scattering spectroscopy, and transmission electron microscopy are used to examine the GaSb(100) surfaces grown by molecular beam epitaxy after thermal desorption of a protective As or Sb layer and subsequent atomic layer deposition (ALD) of Al₂O₃. An antimony protective layer is found to be more favorable compared to an arsenic capping layer as it prevents As alloys from forming with the GaSb substrate. The evolution of oxide free GaSb/Al₂O₃ interface is investigated by "half-cycle" ALD reactions of trimethyl aluminum and deionized water.