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Encapsulation and contacting of two-dimensional materials

Periodic Reporting for period 1 - ECOMAT (Encapsulation and contacting of two-dimensional materials)

Reporting period: 2018-06-01 to 2020-05-31

In this project the encapsulation and contacting of graphene and MoS2 was investigated. Graphene is one monolayer of carbon arranged a two dimensional (2D) honeycomb lattice, which is very promising for several applications in the semiconductor technology. The remarkable performance of the first experimental graphene devices gave rise to a new era of atomically thin materials in solid-state electronics. After some years so-called 2D materials beyond graphene began to be studied, for example transition metal dichalcogenides (TMDCs) that are atomically thin semiconductors of the type MX2, where a transition metal atom (M = Mo, W, We and so on) is sandwiched between two chalcogen atoms (X = S, Se, Te and so on). The advantage of TMDs over graphene, which conducts electricity very well, is that they are true semiconductors, which makes them perfectly suited for electronics and optoelectronics applications. But one problem remains the same: a device fabrication that retains the properties of these materials and approaches values close to what is theoretically possible. Although significant research has been performed, we still lack the knowledge of how to build a device that works with 100% of possible performance. Especially the interfaces on top of 2D materials are critical for the overall device performance, and suitable deposition techniques for them need to be developed. This project had as objectives to study the oxide deposition by means of atomic layer deposition on top of graphene and MoS2 and to build different kinds of test devices to assess their performance. In addition, contacting 2D materials with ohmic contacts after their encapsulation was investigated.
This project was divided in two parts. One part was the management, training, dissemination and exploitation and the second part was technical with the main objective being to build and test the electrical performance of graphene and MoS2 devices. The management, the reporting and the communication with EC as well as the transferable skills - especially communication with colleagues and the improvement of language skills - was done on a day-by-day basis during the entire project duration. The training was received in the first months and from then on whenever necessary. Dissemination and exploitation activities included publications (3 papers and 1 in preparation) and 4 workshops that the researcher participated in during the time of the project. In the second part, the technical part, the fabrication and electrical characterization of devices made of graphene and MoS2 was performed. The fabrication process was developed along with a systematic study of the oxide deposition on top of graphene and MoS2. This included using a 2D material, hexagonal monolayer boron nitride (hBN), as an intermediate layer between the deposited oxide and the graphene or MoS2 to see if it would a) protect the graphene or MoS2 from damage during deposition of the oxide and b) decrease electrostatic or chemical interactions between graphene/MoS2 and the oxide, thereby increasing device performance. The characterization and evaluation of the oxide deposition and other process steps was done using different microscopy techniques, Raman spectroscopy and electrical measurement of the fabricated devices. Parts 1 and 2 of the project were completed successfully both in terms of the development of the researcher’s personal skills and the contribution to the scientific community.
The impact of this project is knowledge generation, academic science that could be used in the semiconductor industry. In the case of this project our objectives were to contribute with the knowledge to build a device with an acceptable performance. To achieve this, a systematic characterization of the fabrication process was necessary. This knowledge will be used in future work. Regarding her personal career, the researcher has decided to keep working in academia. The skills developed during the fellowship in terms of scientific research, teaching and project management are perfect for this. She enjoyed working in Germany and she will continue her work at the University of Wuppertal, in Wuppertal, Germany. The research activities of this project will be further continued within a collaboration with an European High Tech company.