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Stacked hetero-structures of two-dimensional materials allow for a design of interactions with corresponding electronic and mechanical properties.

Combining graphene and the insulating hexagonal boron nitride (h-BN) into two-dimensional heterostructures is promising for novel, atomically thin electronic nanodevices. A heteroepitaxial growth, in which these materials are grown on top of each other, will be crucial for their scalable device integration. However, during this so-called van der Waals epitaxy, not only the atomically thin substrate itself must be considered but also the influences from the supporting substrate below it. Here, we report not only a substantial difference between the formation of h-BN on single- (SLG) and on bi-layer epitaxial graphene (BLG) on SiC, but also vice versa, that the van der Waals epitaxy of h-BN at growth temperatures well below 1000 °C affects the varying number of graphene layers differently. Our results clearly demonstrate that the additional graphene layer in BLG enhances the distance to the corrugated, carbon-rich interface of the supporting SiC substrate and thereby diminishes its influence on the van der Waals epitaxy, leading to a homogeneous formation of a smooth, atomically thin heterostructure, which will be required for a scalable device integration of 2D heterostructures.

The implementation of graphene in different applications will only be possible if the large‐area and high‐quality production of this material becomes a reality. The ideal synthesis method would allow for precisely controlled formation of graphene layers directly on a substrate of choice. In that context, MBE appears as a promising alternative. The growth by this technique does not involve catalytic processes and could in principle be extended to different substrates. One of the main advantages of MBE is that it offers the benefit of exact deposition rates and sub‐monolayer thickness precision. This is especially attractive regarding fundamental growth studies as well as the preparation of graphene films with a specific number of atomic layers. In this chapter an overview of the results achieved by different groups on MBE growth of graphene will be presented.

Hexagonal boron nitride (h-BN) is a wide band gap layered material that is promising for a plethora of applications ranging from neutron detection to quantum information processing. Moreover, it has become highly relevant in the field of two-dimensional crystals and their van der Waals heterostructures due to its multiple functionality as substrate, encapsulation layer, tunneling barrier, or dielectric layer in various device schemes. Hence, controlled synthesis of h-BN has been intensively pursued aiming at its future implementation into different technologies. Herein, recent progress in growth of h-BN, either as bulk crystals or large-area thin films with thicknesses varying from tens of micrometers down to a single atomic layer, is reviewed. A general description of the main methods utilized including their technical aspects is presented in conjunction with the discussion of the material properties determined using well-established characterization tools. Also the main challenges and application prospects of each growth approach are addressed.

As different low-dimensional materials are sought to be incorporated into microelectronic devices, graphene integration is dependent on the development of band gap opening strategies. Amidst the different methods currently investigated, application of strain and use of electronic quantum confinement have shown promising results. In the present work, epitaxial graphene nanoribbons (GNR), formed by surface graphitization of SiC (0001) on crystalline step edges, were submitted to photochemical chlorination. The incorporation of Cl into the buffer layer underlying graphene increased the compressive uniaxial strain in the ribbons. Such method is a promising tool for tuning the band gap of GNRs.

Scalable fabrication of magnetic 2D materials and heterostructures constitutes a crucial step for scaling down current spintronic devices and the development of novel spintronic applications. Here, we report on van der Waals (vdW) epitaxy of the layered magnetic metal Fe3GeTe2 (FGT) - a 2D crystal with highly tunable properties and a high prospect for room temperature ferromagnetism (FM) - directly on graphene by employing molecular beam epitaxy. Morphological and structural characterization confirmed the realization of large-area, continuous FGT/graphene heterostructure films with stable interfaces and good crystalline quality. Furthermore, magneto-transport and x-ray magnetic circular dichroism investigations confirmed a robust out-of-plane FM in the layers, comparable to state-of-the-art exfoliated flakes from bulk crystals. These results are highly relevant for further research on wafer-scale growth of vdW heterostructures combining FGT with other layered crystals such as transition metal dichalcogenides for the realization of multifunctional, atomically thin devices., They also acknowledge the provision of beamtime under the project HC-4068 at the European Synchrotron Radiation Facility (ESRF), located in Grenoble (France). ICN2 researchers acknowledge support from the European Union Horizon 2020 research and innovation programme under Grant Agreement No. 881603 (Graphene Flagship).

Scalable fabrication of atomically thin hexagonal boron nitride (h-BN) films is highly important for the future implementation of this two-dimensional dielectric in various applications. In this contribution, we report on systematical growth experiments of few-layer thick h-BN, synthesized by molecular beam epitaxy (MBE), on crystalline Ni films deposited on MgO(111). The samples are studied using scanning electron microscopy, atomic force microscopy, Raman spectroscopy, and synchrotron-based grazing incidence diffraction. Growth parameters for the realization of continuous h-BN films with high structural quality are presented and discussed. Additionally, our study also aims at gaining insight into the nucleation and growth behavior of h-BN on the Ni surface, which is crucial for achieving further improvement in terms of crystal quality and thickness homogeneity of h-BN layers grown not only by MBE but also by other methods.

The miniaturization of metal-oxide-semiconductor field effect transistors (MOSFETs) is approaching fundamental limits. Novel materials and innovative device structures are needed in order to continue the evolution of complementary metal-oxide-semiconductor (CMOS) technology. High-k dielectrics combined with semiconductors with superior transport properties than Si is an attractive alternative for future CMOS applications. For instance, the use of germanium as a high-mobility channel material is very promising due to intrinsic higher carrier mobilities than Si [1]. However, one of the issues that still remains is the challenge to achieve a high quality interface between Ge and a high-k gate dielectric. Although different methods have been employed for surface passivation prior to the high-k deposition (e.g. thermally grown GeO2 [2]), their use may impede further equivalent oxide thickness (EOT) scaling to values 1nm. Therefore, the search for alternative high-k oxides that could offer stable interfaces with a low density of electrically active defects has become a topic of major interest. Ternary rare earth oxides such as the scandates (LaScO3 or GdScO3) and LaLuO3, were proven to be promising high-k dielectric candidates on silicon. Thin films of these materials keep their amorphous structure up to 1000°C, as measured by X-ray diffraction (not shown). In addition, as summarized in table 1, they offer large optical band gaps (>5 eV) and band offsets to silicon (2-2.5 eV), and have dielectric constants (k) between 23 up to 32 [3]. The integration of these oxides with high mobility substrates such as Ge, SiGe, and strained Si (sSi) also shows great potential [4,5]. Figure 1 illustrates capacitance-voltage (C-V) measurements for a ~4.5 nm thick amorphous LaLuO3 film deposited directly on n-type Ge(100) substrates without any surface passivation layer. C-V curves free of humps and irregularities could be obtained. When comparing curves measured at different frequencies, one can see a dispersion of less than 5% on the accumulation side and a small flatband voltage shift of about 0.2 V between 10 kHz and 1 MHz. Most importantly, an EOT below 1 nm could be achieved with leakage current densities kept below 10 A/cm and Dit levels in the range of 1 to 5x10 eVcm. These and other similar results obtained for scandate films on Ge (not shown) will be discussed taking into account the physico-chemical scenario at the oxide/Ge interface as studied by X-ray photoelectron spectroscopy, transmission electron microscopy and time-of-flight secondary ion mass spectrometry. It will be shown that the formation of a germanate-like interface between the oxide and Ge results in an improvement of the electrical properties.

We investigated the electrical and structural properties of TbScO3 as an alternative gate dielectric. Rutherford backscattering spectrometry revealed a stoichiometric film while X-ray photo-electron spectroscopy indicated silicate formation at the interface. Capacitance-Voltage measurements resulted in well behaving C-V curves with no hysteresis and a low density of interface trap states in the range of 4x1011 (eVcm2)-1. Fully depleted (FD) SOI and sSOI MOSFETs fabricated with a full replacement gate process show a steep subthreshold slope down to 81 mV/dec and high Ion/Ioff ratios up to 108. Low field electron mobilities of 181 cm2/Vsec for SOI and 350 cm2/Vsec for sSOI, were extracted, which are comparable to MOSFETs with Hf based oxides. Gate induced drain leakage (GIDL) investigations indicate a trap assisted band to band tunneling.

Achieving the controlled and large-area synthesis of multilayer graphene on SiC(000–1) surfaces is still an ongoing challenge. Here, we present systematical results on the growth of multilayer thick graphene films on the C-face of SiC by employing an adaptation of the so-called confinement controlled sublimation method. Practical features of the synthesis process, which are very important to attain reproducible data, are discussed in detail. The graphene films were characterized using atomic force microscopy and Raman spectroscopy. The variation of the growth time allowed for the final average thickness of the graphene coverage to be varied. The synthesized multilayer graphene films offer high structural quality and are continuous over large areas. Strikingly, the results show that although the initial quality of the substrate surface does not impact the defect density in the graphene layers, it seems to directly affect the stacking arrangement of the adjacent graphene layers, which in turn, influence their electronic (de)coupling.

The capacitance of series LaScO3-SiO2 capacitors on Si substrates has been investigated in the same DC bias range and at the same operation frequencies by admittance and scanning microwave microscopy (SMM) measurements on the 10(-3) cm2 scale and 100 nm2 scale, respectively. By SMM measurements it is shown that changes in the series capacitance due to local current flows persist and that such nanoscale changes can be induced by slow speed SMM scans at a constant DC bias.

The paper presents the results of electrical characterization in the wide temperature range (120 - 320 K) of the interface and bulk properties of high-k LaLuO3 dielectric deposited by molecular beam deposition (MBD) on silicon substrate. The energy distribution of interface state density is presented and typical maxima of 1.2×1011 and 2.5×1011 eV-1cm-2 were found at about 0.25 - 0.3 eV from the silicon valence band. The charge carrier transport through the dielectric at the forward bias was found to occur via Poole-Frenkel mechanism, while variable range hopping conduction (Mott's law) controls the current at the reverse bias.