Functional Electrical Contacts to Two-Dimensional Materials with Tunable Interfacial Oxides

Project Information

ProTOC

Grant agreement ID: 841556

DOI

10.3030/841556

Project closed

EC signature date 2 April 2019

Start date 1 June 2019

End date 30 November 2020

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 131 104,80

EU contribution

€ 131 104,80

Coordinated by

TECHNISCHE UNIVERSITAET MUENCHEN
Germany

Periodic Reporting for period 1 - ProTOC (Functional Electrical Contacts to Two-Dimensional Materials with Tunable Interfacial Oxides)

Reporting period: 2019-06-01 to 2020-11-30

Summary of the context and overall objectives of the project

The project focused on the large-scale integration of two-dimensional (2D) van der Waals (vdW) materials with other bulk materials using remote plasma-assisted atomic layer deposition (ALD) to establish the foundation for future optoelectronics devices. 2D materials have unique properties to augment current semiconductor technology vital for future nanoelectronics. Unlike monolithic bulk materials, the weak vdW forces between the layers in 2D materials release lattice matching conditions, thus allow forming novel heterostructures of desired properties. However, making electrical contacts to 2D materials and their integration with dielectrics is challenging because it often requires harsh growth and processing conditions involving plasma, elevated temperatures, and reactive chemicals deleterious to the vdW surface and the performance of 2D devices. Thus, a major challenge for 2D device fabrication and applications is integrating them with other bulk materials without creating defects in the 2D material. The ProTOC project’s goal was to explore ultrathin nitrides and oxides, grown by ALD, as protective coatings for 2D materials, to create novel 2D/3D heterostructures, and interfacial layers to conformally contact 2D materials and prevent damages to the 2D material during metal deposition. ALD allows for precise control of the material’s thickness and composition to tune electronic properties, such as work function, dielectric constant, and defect concentrations. In conclusion, ProTOC demonstrates the damage-free deposition of dielectrics, semiconductors and metals on 2D materials on a large-scale by ALD, which is compatible with semiconductor technology. Beyond the application for 2D materials, the ALD processes developed during this project are relevant to the semiconductor industry and device engineering. Overall, the accomplishments in ALD in the context of devices will lead to further technological breakthroughs resulting in patents and consumer products beneficial for the industry, research and economy.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

ProTOC has contributed many exciting results to different fields, including materials science, device engineering and semiconductor physics, and resulted in new collaborations and research proposals with academia and industry in several directions. The key outcomes on the different aspects of ProTOC will be published by 2021 in over 5 peer-reviewed articles, of which the fellow will be the lead author. First of all, ProTOC resulted in new ALD recipes and processes for the self-limiting growth of ultrathin (< 1 nm), yet continuous films at temperatures below 100 °C. Such a low process temperature is compatible with polymer-based lithography and lift-off processing. Second, the fellow developed ALD recipes for the growth of aluminium nitride (AlN) and aluminium oxide (AlOx) directly on 2D materials and demonstrated that these ALD films are weakly adsorbed (vdW-bonded) to 2D molybdenum disulfide (MoS2). The research demonstrated the large-scale and damage-free encapsulation of 2D MoS2 with AlN and AlOx by remote plasma-assisted ALD at growth temperatures near room temperature (40 °C), providing a scalable alternative to hexagonal boron nitride. Because ALD is conformal, it enables the full enclosure of the 2D material and protects the 2D material from corrosion. Third, the fellow created 2D transistors combined with ALD-grown adlayers. X-ray photoelectron spectroscopy (XPS) analysis and electrical measurements of ALD encapsulated MoS2 transistors demonstrated controlled band alignment via charge transfer doping of MoS2 by ALD AlN and AlOx adlayers, as well as stability in the air under device operation.
Additional key outcomes include the ALD growth of a 2D amorphous and continuous AlOx monolayer and the creation of novel substrate-embedded metallic and dielectric structures. ALD-grown ultrathin and embedded dielectric coatings enabled area-selective growth of MoS2 by chemical vapour deposition (CVD), one of the biggest challenges of 2D materials. Notably, the researcher was awarded measurement time at three large-scale research facilities in Europe for his proposed research on the substrate- and layer-dependent effects in 2D materials: A. Henning, I.D. Sharp (2020): Accepted beamtime at synchrotrons Elettra, Trieste (Italy), Paul-Scherrer Institute, Villigen (Switzerland) and MAX IV, Lund (Sweden), 2020. The results achieved during these experiments will lead to additional journal publications related to the layer- and substrate-dependent Scanning Photoelectron Microscopy of Single-Crystalline MoS2.
The exploitable results further include developed new ALD processes, established new connections to representatives from industry and scientists from other departments and research facilities, and new research proposals and endeavours that emerged from ProTOC. Moreover, the fellow established relationships to scientists at Universities across Europe during experiments at synchrotron facilities and engaged with researchers from various departments at TUM. TUM ForTe currently assesses the patentability of developed ALD processes for the surface functionalisation of III-V semiconductors, developed during this project. The established connections to staff scientists at three synchrotrons in Europe during the project will help organise subsequent experiments at these facilities. The results achieved during the project led to new collaborations on several new projects. All in all, ProTOC outcomes were and will be presented at various international scientific conferences.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

ProTOC demonstrates surface functionalisation and control of III-V semiconductors’ interface properties with ALD-grown continuous monolayer coatings. This outcome is relevant to the semiconductor industry and established an industrial-academic partnership between the Sharp Group and Infineon Technologies AG on ALD. The dielectric environment largely controls the properties of 2D materials, and the improved fundamental understanding of 2D/3D heterostructures is vital for 2D materials community and 2D device engineering. The possibility of vdW-bonded dielectrics on 2D materials is demonstrated in this work, and it provides an important milestone for the damage-free integration of 2D materials with bulk materials such as silicon. Therefore, this work provides a scalable route to the dielectric integration and encapsulation of 2D materials critical for future 2D materials-based optoelectronics. Moreover, this research paves the way for other plasma-assisted ALD processes for sensitive materials including vdW materials, organic materials and hybrid organic-inorganic perovskites.

Schematics of 2D transistor and 2D/ALD layer interfaces.