Browsing by Author "Khosravi, Ava"
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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 Dual-Gate MoS₂ Transistors with Sub-10 NM Top-Gate High-K Dielectrics(American Institute of Physics Inc.) Bolshakov, Pavel; Khosravi, Ava; Zhao, Peng; Hurley, P. K.; Hinkle, Christopher L.; Wallace, Robert M.; Young, Chadwin D.; 0000-0002-3530-6400 (Zhao, P); 0000-0001-5566-4806 (Wallace, RM); 0000-0003-0690-7423 (Young, CD); Bolshakov, Pavel; Khosravi, Ava; Zhao, Peng; Hinkle, Christopher L.; Wallace, Robert M.; Young, Chadwin D.High quality sub-10 nm high-k dielectrics are deposited on top of MoS₂ and evaluated using a dual-gate field effect transistor configuration. Comparison between top-gate HfO₂ and an Al₂O₃/HfO₂ bilayer shows significant improvement in device performance due to the insertion of the thin Al₂O₃ layer. The results show that the Al₂O₃ buffer layer improves the interface quality by effectively reducing the net fixed positive oxide charge at the top-gate MoS₂/high-k dielectric interface. Dual-gate sweeping, where both the top-gate and the back-gate are swept simultaneously, provides significant insight into the role of these oxide charges and improves overall device performance. Dual-gate transistors encapsulated in an Al₂O₃ dielectric demonstrate a near-ideal subthreshold swing of ~60 mV/dec and a high field effect mobility of 100 cm²/V·s.Item Enhancing Interconnect Reliability and Performance by Converting Tantalum to 2D Layered Tantalum Sulfide at Low Temperature(Wiley-VCH Verlag, 2019-06-11) Lo, C. -L; Catalano, Massimo; Khosravi, Ava; Ge, W.; Ji, Y.; Zemlyanov, D. Y.; Wang, Luhua; Addou, Rafik; Liu, Y.; Wallace, Robert M.; Kim, Moon J.; Chen, Z.; 0000-0001-5566-4806 (Wallace, RM); Catalano, Massimo; Khosravi, Ava; Wang, Luhua; Addou, Rafik; Wallace, Robert M.; Kim, Moon J.The interconnect half-pitch size will reach ≈20 nm in the coming sub-5 nm technology node. Meanwhile, the TaN/Ta (barrier/liner) bilayer stack has to be >4 nm to ensure acceptable liner and diffusion barrier properties. Since TaN/Ta occupy a significant portion of the interconnect cross-section and they are much more resistive than Cu, the effective conductance of an ultrascaled interconnect will be compromised by the thick bilayer. Therefore, 2D layered materials have been explored as diffusion barrier alternatives. However, many of the proposed 2D barriers are prepared at too high temperatures to be compatible with the back-end-of-line (BEOL) technology. In addition, as important as the diffusion barrier properties, the liner properties of 2D materials must be evaluated, which has not yet been pursued. Here, a 2D layered tantalum sulfide (TaSₓ) with ≈1.5 nm thickness is developed to replace the conventional TaN/Ta bilayer. The TaSx ultrathin film is industry-friendly, BEOL-compatible, and can be directly prepared on dielectrics. The results show superior barrier/liner properties of TaSₓ compared to the TaN/Ta bilayer. This single-stack material, serving as both a liner and a barrier, will enable continued scaling of interconnects beyond 5 nm node. ©2019 WILEY-VCH Verlag GmbH & Co. KGaA, WeinheimItem 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 Sensitivity of High-k Encapsulated MoS₂ Transistors to I-V Measurement Execution Time(Institute of Electrical and Electronics Engineers Inc.) Bolshakov, Pavel; Khosravi, Ava; Zhao, Peng; Wallace, Robert M.; Young, Chadwin D.; Hurley, P. K.; Bolshakov, Pavel; Khosravi, Ava; Zhao, Peng; Wallace, Robert M.; Young, Chadwin D.High-k encapsulated MoS₂ field-effect-transistors were fabricated and electrically characterized. Comparison between HfO₂ and Al₂O₃ encapsulated MoS₂ FETs and their I-V response to execution time are shown. Changes in gate voltage step and integration time demonstrate that electrical characterization parameters can significantly impact device parameters such as the subthreshold swing and the threshold voltage. © 2018 IEEE.Item Surface and Interface Investigation of Novel Materials for Future Applications in Logic and Memory Devices(2020-04-13) Khosravi, Ava; Wallace, Robert M.Layered Transition Metal Dichalcogenides (TMDs) and Ferroelectric Hf0.5Zr0.5O2 (HZO) are the novel material systems investigated in this work for future applications in logic and memory technologies. Semiconductor TMDs exhibited promising electrical properties for device applications beyond silicon-based electronics. For the implementation of semiconductor TMDs into nano-electronic devices, challenges like a viable doping approach and a high-quality semiconductor-dielectric interface need to be addressed. This work provides surface engineering techniques to overcome the doping and dielectric deposition challenges for WSe2 and ReS2. Insitu XPS, AFM, and Raman are among the characterization techniques employed in this work to provide a thorough surface and interface analysis of WSe2 and ReS2. HZO thin films are considered potential materials for future ferroelectric memory devices because of being highly scalable and compatible with CMOS technology. Integration of ferroelectric HZO thin films into the commercial ferroelectric random-access memory (Fe-RAM) and ferroelectric field-effect transistor (Fe-FET) still needs considerable improvement. Therefore, the fundamental study of the evolution of the HZO interfaces remains to be systematically characterized. In this work, the HZO deposition process on metal and semiconductor is therefore investigated in detail by interrupting the ALD growth cycle and in-situ surface characterization using monochromatic XPS.