The stacking of two-dimensional layered materials, such as semiconducting transition metal dichalcogenides (TMDs), insulating hexagonal boron nitride (hBN), and semimetallic graphene, has been theorized to produce tunable electronic and optoelectronic properties. Here we demonstrate the direct growth of MoS2, WSe2, and hBN on epitaxial graphene to form large-area van der Waals heterostructures. We reveal that the properties of the underlying graphene dictate properties of the heterostructures, where strain, wrinkling, and defects on the surface of graphene act as nucleation centers for lateral growth of the overlayer. Additionally, we show that the direct synthesis of TMDs on epitaxial graphene exhibits atomically sharp interfaces. Finally, we demonstrate that direct growth of MoS2 on epitaxial graphene can lead to a 10(3) improvement in photoresponse compared to MoS2 alone.

Hexagonal boron nitride (h-BN) is a promising dielectric material for graphene-based electronic devices. Here we investigate the potential of h-BN gate dielectrics, grown by chemical vapor deposition (CVD), for integration with quasi-freestanding epitaxial graphene (QFEG). We discuss the large scale growth of h-BN on copper foil via a catalytic thermal CVD process and the subsequent transfer of h-BN to a 75 mm QFEG wafer. X-ray photoelectron spectroscopy (XPS) measurements confirm the absence of h-BN/graphitic domains and indicate that the film is chemically stable throughout the transfer process, while Raman spectroscopy indicates a 42% relaxation of compressive stress following removal of the copper substrate and subsequent transfer of h-BN to QFEG. Despite stress-induced wrinkling observed in the films, Hall effect measurements show little degradation (<10%) in carrier mobility for h-BN coated QFEG. Temperature dependent Hall measurements indicate little contribution from remote surface optical phonon scattering and suggest that, compared to HfO(2) based dielectrics, h-BN can be an excellent material for preserving electrical transport properties. Graphene transistors utilizing h-BN gates exhibit peak intrinsic cutoff frequencies >30 GHz (2.4× that of HfO(2)-based devices).

We present a route for direct growth of boron nitride via a polyborazylene to h-BN conversion process. This two-step growth process ultimately leads to a >25x reduction in the RMS surface roughness of h-BN films when compared to a high temperature growth on Al 2 O 3 (0001) and Si (111) substrates. Additionally, the stoichiometry is shown to be highly dependent on the initial polyborazylene deposition temperature.Importantly, CVD graphene transferred to direct-grown boron nitride films on Al 2 O 3 at 400°C results in a >1.5x and >2.5x improvement in mobility compared to CVD graphene transferred to Al 2 O 3 and SiO 2 substrates, respectively, which is attributed to the combined reduction of remote charged impurity scattering and surface roughness scattering. Simulation of mobility versus carrier concentration confirms the importance of limiting the introduction of charged impurities in the h-BN film and highlights the importance of these results in producing optimized h-BN substrates for high performance graphene and TMD devices.

Thermal conductivity of freestanding 10 nm and 20 nm thick chemical vapor deposited hexagonal boron nitride films was measured using both steady state and transient techniques. The measured value for both thicknesses, about 100 ± 10 W m−1 K−1, is lower than the bulk basal plane value (390 W m−1 K−1) due to the imperfections in the specimen microstructure. Impressively, this value is still 100 times higher than conventional dielectrics. Considering scalability and ease of integration, hexagonal boron nitride grown over large area is an excellent candidate for thermal management in two dimensional materials-based nanoelectronics.

Hexagonal boron nitride (h-BN) atomic layers are synthesized on polycrystalline copper foils via a novel chemical vapor deposition (CVD) process that maintains a vapor-phase copper overpressure during growth. Compared to h-BN films grown without a copper overpressure, this process results in a >10× reduction of 3-dimensional BN fullerene-like surface features, a reduction of carbon and oxygen contamination of 65% and 62%, respectively, an increase in h-BN grain size of >2×, and an 89% increase in electrical breakdown strength.

A 400Gbps PAM-4 fully integrated DR4 silicon photonics transmitter with four heterogeneously integrated DFB lasers has been demonstrated for data center applications over a temperature range of 0~70°C and a reach of up to 2km

We present a comprehensive study on the integration of hexagonal boron nitride (h‐BN) with epitaxial graphene (EG) and bilayer hydrogen intercalated EG. Charged impurity scattering is the dominant scattering mechanism for as‐grown and h‐BN coated graphene. Use of h‐BN dielectrics leads to a 2.6× improvement in Hall mobility relative to HfO2 by introducing less charged impurities and negligible additional remote surface optical scattering beyond that introduced by the substrate. Temperature dependent mobility measurement is used to link the surface morphology of the silicon carbide substrate (i.e., step‐edge density) with charge carrier transport, showing that significant degradation in mobility can result from increased remote charged impurity as well as remote surface optical scattering at the SiC step‐edges. Furthermore, we demonstrate that the integration of h‐BN with EG and bilayer graphene presents unique challenges compared to previous works on exfoliated graphene, where the benefits of h‐BN as a dielectric is highly dependent on the initial quality of the EG. To this end, modeling of the carrier mobility as a function of impurity density is used to identify the regimes where h‐BN dielectrics outperform conventional dielectrics and where they fail to surpass them. Modeling indicates that h‐BN can ultimately lead to a >5× increase in mobility relative to HfO2 dielectrics due to higher energy surface optical phonon (SOP) modes.

A fully integrated 800 Gbps PAM-4 2×FR4 and DR8 silicon photonics transmitter with eight heterogeneously integrated DFB lasers is demonstrated for data center applications over a temperature range of 0~70°C and a reach of up to 2 km.