Browsing by Author "Wang, Qingxiao"
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Item Al₂O₃ on WSe₂ by Ozone Based Atomic Layer Deposition: Nucleation and Interface StudyAzcatl, Angelica; Wang, Qingxiao; Kim, Moon J.; Wallace, Robert M.; 0000-0001-5566-4806 (Wallace, RM); Azcatl, Angelica; Wang, Qingxiao; Kim, Moon J.; Wallace, Robert M.In this work, the atomic layer deposition process using ozone and trimethylaluminum (TMA) for the deposition of Al₂O₃ films on WSe₂ was investigated. It was found that the ozone-based atomic layer deposition enhanced the nucleation of Al₂O₃ in comparison to the water/TMA process. In addition, the chemistry at the Al₂O₃ / WSe₂ interface and the surface morphology of the Al₂O₃ films exhibited a dependence on the deposition temperature. A non-covalent functionalizing effect of ozone on WSe₂ at low deposition temperatures 30 ⁰C was identified which prevented the formation of pinholes in the Al₂O₃ films. These findings aim to provide an approach to obtain high-quality gate dielectrics on WSe₂ for two-dimensional transistor applications.Item Cubic Crystalline Erbium Oxide Growth on GaN(0001) by Atomic Layer Deposition(Amer Inst Physics, 2018-10-22) Chen, Pei-Yu; Posadas, Agham B.; Kwon, Sunah; Wang, Qingxiao; Kim, Moon J.; Demkov, Alexander A.; Ekerdt, John G.; Kwon, Sunah; Wang, Qingxiao; Kim, Moon J.Growth of crystalline Er₂O₃, a rare earth sesquioxide, on GaN(0001) is described. Ex situ HCl and NH₄OH solutions and an in situ N₂ plasma are used to remove impurities on the GaN surface and result in a Ga/N stoichiometry of 1.02. Using atomic layer deposition with erbium tris(isopropylcyclopentadienyl) [Er((^{i}PrCp)₃] and water, crystalline cubic Er₂O₃ (C-Er₂O₃) is grown on GaN at 250 ⁰C. The orientation relationships between the C-Er₂O₃ film and the GaN substrate are C-Er₂O₃(222)Item In Situ Characterization of Phase Transition and Defect Dynamics in Molybdenum Ditelluride(2020-04-17) Wang, Qingxiao; Kim, Moon J.; Wallace, Robert M.Transition metal dichalcogenides (TMDs) are regarded as promising materials for emerging applications, including electronic devices, photonic devices, biosensors, and energy storage, etc. Owing to their novel structures and extraordinary properties, they have provided the researchers with an excellent platform to explore low-dimensional physics. However, some challenges need to be resolved before their practical application. The phases and defects in TMDs can significantly affect their properties. Therefore, understanding the phase transition and defects in TMDs would be of great importance to advance their further application. This dissertation focuses on the identification and characterization of a novel phase transition from two dimensional MoTe2 phase to one dimensional Mo6Te6 nanowire phase during the vacuum annealing. Furthermore, the thermal stability of MoTe2 is extensively investigated. In particular, the inversion domain boundaries formed during the vacuum annealing are identified to be a defective interface in MoTe2. The role of Te vacancy to the evolution of inversion domain boundaries is extensively studied. Also, a possible strategy to improve its thermal stability is demonstrated.Item Metal-Organic Chemical Vapor Deposition of High Quality, High Indium Composition N-Polar InGaN Layers for Tunnel Devices(American Institute of Physics Inc, 2018-08-24) Lund, C.; Romanczyk, B.; Catalano, Massimo; Wang, Qingxiao; Li, W.; DiGiovanni, D.; Kim, Moon J.; Fay, P.; Nakamura, S.; DenBaars, S. P.; Mishra, U. K.; Keller, S.; Catalano, Massimo; Wang, Qingxiao; Kim, Moon J.In this study, the growth of high quality N-polar InGaN films by metalorganic chemical vapor deposition is presented with a focus on growth process optimization for high indium compositions and the structural and tunneling properties of such films. Uniform InGaN/GaN multiple quantum well stacks with indium compositions up to 0.46 were grown with local compositional analysis performed by energy-dispersive X-ray spectroscopy within a scanning transmission electron microscope. Bright room-temperature photoluminescence up to 600 nm was observed for films with indium compositions up to 0.35. To study the tunneling behavior of the InGaN layers, N-polar GaN/In0.35Ga0.65N/GaN tunnel diodes were fabricated which reached a maximum current density of 1.7 kA/cm2 at 5 V reverse bias. Temperature-dependent measurements are presented and confirm tunneling behavior under reverse bias. © 2017 Author(s).Item Realization of the First GaN Based Tunnel Field-Effect Transistor(Institute of Electrical and Electronics Engineers Inc.) Chaney, A.; Turski, H.; Nomoto, K.; Wang, Qingxiao; Hu, Z.; Kim, Moon J.; Xing, H. G.; Jena, D.; Wang, Qingxiao; Kim, Moon J.Tunnel field-effect transistors (TFETs) offer the means to surpass the subthreshold swing (SS) limit of 60 mV/dec that limits MOSFETs. While MOSFETs rely on modulating a potential barrier, which is subject to a Boltzmann tail in the density of states (DOS), interband tunneling in TFETs enables a sharp turn off of the DOS because the transport is no longer governed by an exponential tail of carriers. These devices have been investigated in Si III-V material systems¹, achieving SS's as low as 20 mV/dec ². GaN is advantageous to these other material systems because its large bandgap is ideal for suppressing leakage current. Unfortunately impurity doping in GaN alone is not enough to achieve the internal fields required to promote interband tunneling[Fig l(a)]. However, by taking advantage of the difference in polarization fields between InGaN and GaN, a device structure favoring interband tunneling can be made [Fig l(b)]. Li et. al.³ have theoretically predicted that a GaN heterojunction TFET could obtain an SS of 15 mV/dec and a peak current of 1× 10⁻⁴ A/µm. For the work being presented, GaN TFETs were fabricated using a surrounding gate (SG) architecture utilizing both nanowires and fins formed from a top-down approach. © 2018 IEEE.