Silane-Catalyzed Fast Growth of Large Single-Crystalline Graphene on Hexagonal Boron Nitride

Abstract: The direct growth of high-quality, large single-crystalline domains of graphene on a dielectric substrate is of vital importance for applications in electronics and optoelectronics. Traditionally, graphene domains grown on dielectrics are typically only ~1 nm with a growth rate of ~1 nm/min or less, the main reason is the lack of a catalyst. Here we show that silane, serving as a gaseous catalyst, is able to boost the graphene growth rate to ~1 um/min, thereby promoting graphene domains up to 20 um in size to be synthesized via chemical vapor deposition on hexagonal boron nitride. Hall measurements show that the mobility of the sample reaches 20,000 cm2/Vs at room temperature, which is among the best for CVD-grown graphene. Combining the advantages of both catalytic CVD and the ultra-flat dielectric substrate, gaseous catalyst-assisted CVD paves the way for synthesizing high-quality graphene for device applications while avoiding the transfer process.

Silane-Catalyzed Fast Growth of Single-Crystalline Graphene on Hexagonal Boron Nitride

This paper details an innovative approach for synthesizing large, single-crystalline graphene domains on hexagonal boron nitride (h-BN) substrates through the use of gaseous catalysts, specifically silane and germane, in chemical vapor deposition (CVD) processes. The challenge addressed is the inherently slow growth rate and limited domain size when growing graphene directly on dielectrics without the use of catalysts. Typically, graphene grown on dielectric substrates such as h-BN lacks the efficiency seen on metal surfaces due to the absence of catalytic enhancement, often resulting in domain sizes under 1 µm and requiring hours to achieve even that.

The research introduces silane, a gaseous silicon compound, as a catalytic agent that markedly accelerates the growth rate of graphene to approximately 1 µm/min, a significant improvement from the conventional ~1 nm/min. This advancement facilitates the fabrication of graphene domains measuring up to 20 µm in size within a 20-minute timeframe, illustrating a substantial enhancement over previous methodologies in terms of both growth rate and domain size.

The paper demonstrates that the integration of silane not only increases growth kinetics but also promotes a high degree of crystallographic alignment of graphene domains on h-BN. The precise alignment is critical for maintaining the electronic properties of graphene, and this study reports mobilities reaching 20,000 cm²/V·s, positioning the synthesized graphene among the highest quality produced through CVD. Notably, Auger electron spectroscopy confirmed the absence of silicon or germanium residues in the graphene, suggesting that the catalytic role of silane does not compromise graphene purity.

The underlying mechanism identified through density functional theory calculations elucidates how silicon atoms bind at the edges of growing graphene domains, substantially reducing the energy barrier required for carbon incorporation and hexagon formation. This catalytic mechanism minimizes the number of reaction steps and energy barriers, thereby enhancing the growth rate.

The practical implications of these findings are significant. By overcoming the need for post-growth transfer processes—which traditionally introduce defects and contamination—this method paves the way for device fabrication within a transfer-free framework. Given the flatness and insulating properties of h-BN, direct growth on this substrate is advantageous for developing high-performance electronic and optoelectronic applications.

Further theoretical exploration could enhance the understanding of the interaction dynamics between catalyst and substrate, potentially optimizing the growth conditions and expanding the scope of application. Future research could investigate additional catalysts or substrate materials that could augment the growth process further or offer new functionalities.

In conclusion, the method presented combines catalytic CVD with h-BN substrates to produce high-quality graphene that meets the stringent requirements of electronic device applications, marking a significant step forward in scalable graphene synthesis on dielectric substrates. As these growth techniques advance, they are likely to have a profound impact on the development and proliferation of graphene-based technologies.