Browsing by Author "Jin, Zehua"
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Item Electrical and Optoelectronic Devices from Two-Dimensional Materials for Advanced and Integrated Functionalities(2018-11-30) Jin, Zehua; Ajayan, Pulickel M.; Lou, JunThe past decade saw rapid development of two-dimensional (2D) layered materials. Being thin and flexible, 2D materials show unique properties as well as high-performance for a variety of electrical and optoelectronic applications. Despite ever-growing progresses on developing 2D materials based devices, there is great amount of room for improving device performance as well as seeking additional functionalities. For example, electrical contact serves as the bottleneck for electrical or optoelectronic devices based on 2D materials. A systematic solution, preferably in large scale, would greatly boost the applicability of 2D materials in various device structures. Talking about semiconductor devices, how to reduce dark current as well as boost device speed has been a major challenge facing photodetectors based on 2D transition metal dichalcogenides. In addition, in real-world applications, many photodetectors work in a more complicated physical principle. For example, image sensors work in a charge integration manner. Can those 2D high-performance photodetectors demonstrate this compatibility? Furthermore, can we further combine the high-performance of 2D optoelectronics with its integrability, to realize its sensitivity on various surfaces? In this thesis, I illustrate my efforts in solving or partially solving the above few questions, aiming to achieve advanced and integrated functionalities of 2D materials. Specifically, I have tried tackling the contact resistance issue by direct synthesis of mixed phase in-planar junctions in large scale. In addition, photodetectors based on III-VI InSe materials as well as its junction structures have been explored for improved photodetection performance. Furthermore, a novel device transfer technique has been developed, enabling the transfer of 2D sensors to a variety of surfaces for near-field sensing applications.Item Fluorinated h-BN as a magnetic semiconductor(American Association for the Advancement of Science, 2017) Radhakrishnan, Sruthi; Das, Deya; Samanta, Atanu; de los Reyes, Carlos A.; Deng, Liangzi; Alemany, Lawrence B.; Weldeghiorghis, Thomas K.; Khabashesku, Valery N.; Kochat, Vidya; Jin, Zehua; Sudeep, Parambath M.; Martí, Angel A.; Chu, Ching-Wu; Roy, Ajit; Tiwary, Chandra Sekhar; Singh, Abhishek K.; Ajayan, Pulickel M.We report the fluorination of electrically insulating hexagonal boron nitride (h-BN) and the subsequent modification of its electronic band structure to a wide bandgap semiconductor via introduction of defect levels. The electrophilic nature of fluorine causes changes in the charge distribution around neighboring nitrogen atoms in h-BN, leading to room temperature weak ferromagnetism. The observations are further supported by theoretical calculations considering various possible configurations of fluorinated h-BN structure and their energy states. This unconventional magnetic semiconductor material could spur studies of stable two-dimensional magnetic semiconductors. Although the high thermal and chemical stability of h-BN have found a variety of uses, this chemical functionalization approach expands its functionality to electronic and magnetic devices.Item Synthesis of High-Quality Graphene and Hexagonal Boron Nitride Monolayer In-Plane Heterostructure on Cu–Ni Alloy(Wiley, 2017) Lu, Guangyuan; Wu, Tianru; Yang, Peng; Yang, Yingchao; Jin, Zehua; Chen, Weibing; Jia, Shuai; Wang, Haomin; Zhang, Guanhua; Sun, Julong; Ajayan, Pulickel M.; Lou, Jun; Xie, Xiaoming; Jiang, MianhengGraphene/hexagonal boron nitride (h-BN) monolayer in-plane heterostructure offers a novel material platform for both fundamental research and device applications. To obtain such a heterostructure in high quality via controllable synthetic approaches is still challenging. In this work, in-plane epitaxy of graphene/h-BN heterostructure is demonstrated on Cu–Ni substrates. The introduction of nickel to copper substrate not only enhances the capability of decomposing polyaminoborane residues but also promotes graphene growth via isothermal segregation. On the alloy surface partially covered by h-BN, graphene is found to nucleate at the corners of the as-formed h-BN grains, and the high growth rate for graphene minimizes the damage of graphene-growth process on h-BN lattice. As a result, high-quality graphene/h-BN in-plane heterostructure with epitaxial relationship can be formed, which is supported by extensive characterizations. Photodetector device applications are demonstrated based on the in-plane heterostructure. The success will have important impact on future research and applications based on this unique material platform.