Browsing by Author "Zhao, Peng"
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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 Investigation of Electrical Properties of Transition Metal Dichalcogenides Transistors with High-K Dielectrics(2018-08) Zhao, Peng; 0000-0002-3530-6400 (Zhao, P); Young, Chadwin D.Recently, transition metal dichalcogenides (TMDs) have attracted intense attention due to their atomic layer-by-layer structure and unique electronic, optical and mechanical properties. Some of them, such as MoS₂ and WSe₂, have demonstrated satisfactory energy bandgap values and promising properties for future applications in electronics and optoelectronics. However, the relatively inert surface of these materials prevents the direct deposition of high-k dielectrics on these 2-D materials. Furthermore, capacitance-voltage (C-V) measurements of high-k dielectric on TMDs and interface defects analysis have not been researched sufficiently. In this dissertation, fabrication, electrical characterization, and simulation of top-gated few-layer TMD transistors are demonstrated with a major focus on interface property study of high-k/TMD. Top-gated capacitors on bulk MoS₂ with 30 nm HfO₂ and Al₂O₃ dielectrics are characterized with C-V and I-V measurements as the early work, showing the necessity of having a more robust test structure and an in-situ surface treatment to enable better interface assessment with quantitatively study. Top-gated few-layer MoS₂ field effect transistors are fabricated using photolithographic patterning, with less than 10 nm thin ALD HfO₂ on MoS₂ after in-situ UV-O₃ surface functionalization. C-V and I-V measurements are performed on these transistors. Interface defect density is extracted and analyzed from C-V measurement results. Annealing effects, such as cleaning effect of ultra-high vacuum annealing before high-k deposition, and N₂ or a forming gas anneal after device fabrication are demonstrated as well. As a comparison, Al₂O₃/MoS₂ interface is also investigated with/without anneals, and the simulation work demonstrates the energetic and spatial distributions of the interface traps. Furthermore, border traps, which are the dielectric traps close to the high-k/MoS₂ interface, are studied based on electrical characterization and simulation, along with the interface traps. The methodologies of fabrication and characterization are also extended to MoSe₂, to understand the high-k/MoSe₂ interface and annealing effects. The electrical characterization and analysis in this dissertation reveal the high-k/TMD interfacial properties, which potentially helps find the origins of those defects and ultimately improves the electrical performance of the TMD devices by passivating the defects.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.