New solutions are needed to further sustain the growth of the semiconductor electronics in the upcoming decades. Both, the size downscaling of metal oxide semiconductor field-effect transistors (MOSFETs) as well as the necessary reduction in power consumption are expectedly limited by physical constrains,  thereby jeopardizing the continuation of  Moore’s law in highly integrated circuits. Thereto, there is a need of novel materials that can replace silicon to enable both scaling below the 3 nm node as well as the realization of disruptive device concepts¹ targeting higher computational power and energy efficiency.

2D semiconductor materials are a class of materials that offer a possible solution to this problem, thanks to their predicted exceptional charge transport properties even at the atomic scales. However, the engineering of experimental electronic and optoelectronic devices based on 2D materials has encountered many challenges that need to be solved in order to fully take advantage of these unique characteristics. In particular, in order to resolve most of the shortcomings that are currently affecting 2D-based electronic devices, like low carrier mobilities and inefficient switching characterized by shallow subthreshold swings, an optimization of the gate dielectric layer and its interface to 2D semiconductor is necessary.

We have recently investigated the growth of a novel 2D material (silicene) on different substrates by means of molecular beam epitaxy^2,3 (MBE) and we have successfully interfaced it with a layer of calcium fluoride⁴ (CaF₂), a promising dielectric material for fabricating ultra-scaled FETs.

Within the advertised doctoral position, this experimental task will be tackled both at the material level, with the integration of well-established high-k oxides and new crystalline insulators, as well as through recurring to innovative strategies, like taking advantage of the negative capacitance (NC) effect found in thin ferroelectric to dielectric stacked layers⁵.

GOALS and METHODS

We will investigate the growth of different epitaxial 2D materials, combining different experimental techniques, from molecular beam epitaxy (MBE) to chemical synthesis. The obtained materials will be fully characterized, recurring to methods on which we have developed a great expertise over the years, such as low-energy electron diffraction (LEED) or photoemission (XPS), Raman and photoluminescence (PL) spectroscopy. The most prominent materials will be selected for fabrication of novel 2D-FET demonstrators and a great focus will be put on realizing and improving the interface between the obtained 2D layers and the insulating materials. In a joint effort with the theoretical work of the PhD project of PI Grasser, we will experimentally investigate new insulating materials such as CaF₂ as well as interfaces built by controlled oxidation and nitridation of 2D materials^6,7 in combination with high-k materials (HfO₂, ZrO₂, Al2O₃), taking advantage of our unique equipment that combines a powerful Plasma-Enhanced Atomic Layer Deposition (PE-ALD) with a high vacuum chamber for growth and characterization. Within the offered position, we will focus both on the device fabrication, from material synthesis to the lithographic definition of the structures, as well as on the electrical characterization of the final device demonstrators. Work will take place in our state-of-the- art clean room facility at the center for micro and nanostructures (ZMNS).

Collaborations

The epitaxially grown 2D materials and engineered insulator interfaces will be developpen in a joint collaboratove effort with theory developped at PhD project of PI Grasser. Further, the novel selected 2D materials will be made available fort he TUDx cooperation partners, in particular for operando PAR-XPS measurements (PI A. Foleske) and for s-SNOM analysis (B. Lendl).

Website:

https://www.tuwien.at/etit/fke/forschung/nanoelektronische-bauelemente

Contact Persons

Prof. Walter Weber

Dr. Daniele Nazzari

Literature:

(1) Fei, W.; Trommer, J.; Lemme, M. C.; Mikolajick, T.; Heinzig, A. Emerging Reconfigurable Electronic Devices Based on Two-Dimensional Materials: A Review. InfoMat 2022, 4

(10), e12355. doi.org/10.1002/inf2.12355, opens an external URL in a new window.

(2) Genser, J.; Nazzari, D.; Ritter, V.; Bethge, O.; Watanabe, K.; Taniguchi, T.; Bertagnolli, E.; Bechstedt, F.; Lugstein, A. Optical Signatures of Dirac Electrodynamics for hBN-Passivated Silicene on Au(111). Nano Lett. 2021, 21

(12), 5301–5307. doi.org/10.1021/acs.nanolett.1c01440, opens an external URL in a new window.

(3) Nazzari, D.; Genser, J.; Ritter, V.; Bethge, O.; Bertagnolli, E.; Ramer, G.; Lendl, B.; Watanabe, K.; Taniguchi, T.; Rurali, R.; Kolíbal, M.; Lugstein, A. Highly Biaxially Strained Silicene on Au(111). J. Phys. Chem. C 2021, 125

(18), 9973–9980. doi.org/10.1021/acs.jpcc.0c11033, opens an external URL in a new window.

(4) Nazzari, D.; Genser, J.; Ritter, V.; Bethge, O.; Bertagnolli, E.; Grasser, T.; Weber, W. M.; Lugstein, A. Epitaxial Growth of Crystalline CaF2 on Silicene. ACS Appl. Mater. Interfaces 2022, 14

(28), 32675–32682. doi.org/10.1021/acsami.2c06293, opens an external URL in a new window.

(5) Salahuddin, S.; Datta, S. Use of Negative Capacitance to Provide Voltage Amplification for Low Power Nanoscale Devices. Nano Lett. 2008, 8

(2), 405–410. doi.org/10.1021/nl071804g, opens an external URL in a new window.

(6) Chamlagain, B.; Cui, Q.; Paudel, S.; Cheng, M. M.-C.; Chen, P.-Y.; Zhou, Z. Thermally Oxidized 2D TaS2 as a High-κ Gate Dielectric for MoS2 Field-Effect Transistors. 2D Mater. 2017, 4

(3), 031002. doi.org/10.1088/2053-1583/aa780e, opens an external URL in a new window.

(7) Lai, S.; Byeon, S.; Kyu Jang, S.; Lee, J.; Hun Lee, B.; Park, J.-H.; Kim, Y.-H.; Lee, S. HfO 2 /HfS 2 Hybrid Heterostructure Fabricated via Controllable Chemical Conversion of Two-Dimensional HfS 2. Nanoscale 2018, 10

(39), 18758–18766. doi.org/10.1039/C8NR06020G, opens an external URL in a new window.