Silicon Carbide Graphene

Silicon carbide graphene is a two-dimensional honeycomb of carbon atoms just one atom thick, offering many desirable characteristics like pure p-conjugation. Flatness is crucial to its stability; to accomplish this goal, its building blocks must also be flat. One way of accomplishing this feat is through flat benzene or chair form hexasilabenzene molecules.

Thermodynamically stable

Silicon carbide graphene’s thermodynamic stability makes it a desirable material for high-end electronics applications, but development remains limited and its stability remains a challenge. This paper addresses both growth and characterization of epitaxial graphene (EG) on SiC, specifically with regard to impact of buffer layer contamination on carrier mobility of graphene carriers.

Synthesis of epitaxial graphene is a challenging task that requires precise control over growth temperature and substrate morphology, in addition to formation of a transition zone between SiC substrate and graphene layer characterized by presence of amorphous carbon and SiC on epitaxial graphene surface known as interfacial layer and measured via surface morphology techniques such as AFM or HR-XTEM measurements.

Graphene is composed of one-atom thick hexagonal sheets connected by bonds. These hexagonals can be stacked in various configurations; most securely in an ABA configuration in which every carbon hexagon from layer A sits directly below a silicon atom from layer B; however other possible stacking configurations include the rhombohedral structure in which carbon tetrahedron centers from A are aligned directly beneath corners from silicon tetrahedrons in B and vice versa.

Rhombohedral graphene structures offer lower energy densities than their ABA counterparts due to having smaller radius tetrahedrons in rhombohedral arrangement than those found in ABA arrangement, and more thermal stability than its ABA equivalents.

The authors have successfully created a large area of single-layer graphene on SiC by combining high-temperature annealing with low-pressure argon ambient. Quick evaluation of graphene quality was accomplished using contrast-enhancing techniques; particularly useful in quickly identifying edges of flake surfaces; this has demonstrated that polar edges of graphene exhibit sharp reflections under polarized light while non-polar edges display weaker resonance properties.

Conductivity

A graphene layer on top of silicon carbide substrate can significantly enhance thermal conductivity at high temperatures due to shorter mean free paths for graphene phonons compared to their SiC crystal lattice counterparts. Experiments have demonstrated this phenomenon experimentally as well as theoretically.

An innovative method has been devised for growing a high-quality graphene layer on SiC ceramic using controlled sublimation (CCS), which achieves near thermodynamic equilibrium while controlling Si vapor density at the growth surface and ensures uniform growth. This technique has proven efficient at producing epitaxial graphene on both Si and C faces of 4H- and 6H-SiC ceramic.

CCS production of graphene is suitable for large-scale use, as its advantage lies in producing larger areas than would otherwise be achievable through other sublimation techniques in unconfined vacuum. Furthermore, CCS allows the formation of an anti-defect buffer layer between SiC substrate and graphene that may help prevent defects forming in graphene layers produced through sublimation methods.

Numerous techniques have been utilized to assess the quality of graphene produced using this method, including low-energy electron microscopy (LEEM), angle-resolved photoelectron spectroscopy (ARPES), and Raman spectroscopy. Raman spectra are employed for investigating structural properties as well as interfaces with other materials, including SiC. Raman’s G peak can detect changes due to doping or strain in its sp2 system and surface modifications on graphene’s surface while D or 2D peaks may reveal modifications on its surface as well.

Non-equilibrium molecular dynamics simulations have revealed both temperature dependence and size effect of graphene/SiC heterostructure electrical conductivities by exploring their temperature dependence and size effects on electrical conductivity. These simulations demonstrated how orientation and stacking sequence of graphene layers are integral in determining their electronic properties; different stacking orders lead to different lattice symmetries which impact band structure as well as interlayer screening properties.

Energy band gap

Silicon carbide graphene’s energy band gap depends on its atomic configuration. When deposited on a born nitride (BN) substrate, graphene exhibits a direct gap. On a silicon carbide (SiC) substrate however, graphene acts more like a semimetal due to the preservation of its p-conjugate orbitals in two-dimensional sheets composed of carbon and silicon; making it a potential material choice for electronic devices requiring low bandgap materials.

Researchers who wish to accurately gauge the energy gap of SiC graphene must first calculate its electron hopping. This can be accomplished using density functional calculations; its hopping energy depends on its nearest-neighbor hopping integral t 1 and its temperature dependence is shown in Fig 2. It varies with Coulomb interaction between electrons and their surroundings and, as such, wider modified gaps result from greater hopping energies.

De Heer et al. conducted an experiment that revealed that monolayer graphene’s energy band gap is very close to that of bulk SiC. They calculated hopping energy for different hopping integrals beyond third nearest-neighbor and utilized this information to determine the modified gap of SiC graphene as a function of temperature.

Their results revealed that monolayer graphene direct gaps on Si-terminated substrates are approximately 1.3 eV, which is very close to its graphite interplane spacing of 3.35 A. Furthermore, these authors calculated hopping energies for both types of substrates; when considering C-terminated ones instead of Si ones the band gap becomes significantly larger by approximately 0.4eV.

This study further illustrates that SiC graphene exhibits strong electronic confinement properties due to its close-packed stacking of carbon layers and strong interactions between their carbon atoms and nearby BN molecules. Furthermore, this research proves that flat SiC p-conjugation is one of the key characteristics of graphene.

A novel method has been devised for growing single and multilayer graphene on both the Si and C surfaces of 4H-SiC using controlled decomposition in an ultrahigh vacuum environment. This allows for growth of high-quality graphene of consistent size while providing excellent control over Si vapor pressure at its surface, essential for graphene production.

Aplicații

Silicon carbide graphene has garnered much interest due to its potential applications across a wide array of fields. With its large band gap, high thermal conductivity, and chemical stability characteristics it makes an appealing candidate for use in electronic devices and sensors. Furthermore, its unique crystal structure makes graphene the most flexible material ever developed. Its properties are determined by its honeycomb-like lattice configuration in which carbon atoms form sp2 bonds on hexagonal matrix structure. Explored using various characterization techniques such as low-energy electron microscopy, angle-resolved photoelectron spectroscopy (ARPES), Raman spectroscopy in various modes, atomic force microscopy with different modes, Hall measurements and others.

Silicon carbide graphene stands out from its peers with exceptional electrical and mechanical properties as well as tolerance of temperature extremes. This makes it suitable for use in various applications ranging from conductive coatings to mechanical components; additionally, etching can produce various nanostructures. There are 170 polytypes of SiC each offering distinct stacking sequences and properties.

Semiconducting graphene boasts an extremely large band gap and room temperature electron mobility that is 20 times larger than other 2D semiconductors. Georgia Institute of Technology researchers have devised a technique for producing wafer-scale single crystal semiconducting epigraphene (SEG) on silicon carbide substrates through quasi equilibrium annealing processes which result in the creation of carbon-rich surface layers on these substrates.

Tromp and Hannon discovered that during the growth of SEG, silicon evaporates from SiC surfaces, leaving behind carbon atoms which can crystallize into multilayer graphene. Their discovery allowed them to control this crystallization using disilane gas to maintain equilibrium of silicon background pressure on SiC surfaces resulting in increased phase transformation temperatures.

Graphene on SiC can be grown through various techniques, with epitaxial growth being the preferred means for producing high-quality mono and multilayer graphene layers. At Graphenic AB we employ an innovative patent protected process for growing graphene on SiC: using a vertical RF inductively heated furnace with porous graphite insulation and graphite crucible; heat is then gradually applied until temperatures of 2000oC have been reached; at this point vacuum release allows control of silicon sublimation so only carbon atoms remain on surfaces of crucible surfaces; at which time sublimation of silicon sublimates off leaving only carbon atoms on surface of crucible surface ensuring only carbon atoms remain on surfaces of crucible surface to ensure high quality graphene production.