3 ms·

Abstract (rest of article behind paywall) Semiconducting graphene plays an important part in graphene nanoelectronics because of the lack of an intrinsic bandg

by tromp 3y ago

Abstract (rest of article behind paywall) Semiconducting graphene plays an important part in graphene nanoelectronics because of the lack of an intrinsic bandgap in graphene1. In the past two decades, attempts to modify the bandgap either by quantum confinement or by chemical functionalization failed to produce viable semiconducting graphene. Here we demonstrate that semiconducting epigraphene (SEG) on single-crystal silicon carbide substrates has a band gap of 0.6 eV and room temperature mobilities exceeding 5,000 cm2 V−1 s−1, which is 10 times larger than that of silicon and 20 times larger than that of the other two-dimensional semiconductors. It is well known that when silicon evaporates from silicon carbide crystal surfaces, the carbon-rich surface crystallizes to produce graphene multilayers2. The first graphitic layer to form on the silicon-terminated face of SiC is an insulating epigraphene layer that is partially covalently bonded to the SiC surface3. Spectroscopic measurements of this buffer layer4 demonstrated semiconducting signatures4, but the mobilities of this layer were limited because of disorder5. Here we demonstrate a quasi-equilibrium annealing method that produces SEG (that is, a well-ordered buffer layer) on macroscopic atomically flat terraces. The SEG lattice is aligned with the SiC substrate. It is chemically, mechanically and thermally robust and can be patterned and seamlessly connected to semimetallic epigraphene using conventional semiconductor fabrication techniques. These essential properties make SEG suitable for nanoelectronics.

gilleain 3y ago
Side-quest : "what the heck is 'epigraphene'?": > Graphene’s original promise to succeed silicon faltered due to pervasive edge disorder in lithographically patterned deposited graphene and the lack of a new electronics paradigm. Here we demonstrate that the annealed edges in conventionally patterned graphene epitaxially grown on a silicon carbide substrate (epigraphene) are stabilized by the substrate and support a protected edge state. From https://www.nature.com/articles/s41467-022-34369-4 https://www.nature.com/articles/s41467-022-34369-4
- jpgvm 3y ago
  > epitaxially Is the keyword you are after. Basically this is a vapour deposition technique of some sort, almost certainly using MBE (molecular beam epitaxy) to grow the graphene on the silicon carbide substrate.
  - adrian_b 3y ago
    While MBE is the best method for many kinds of materials, in this special case a completely different method has been used. Half of silicon carbide is carbon, and by heating silicon carbide at very high temperatures and low pressures the silicon atoms that are close to the surface evaporate, leaving a superficial layer made of carbon. By applying a certain thermal treatment, the carbon layer crystallizes into a layer of monocrystalline graphene. Like for many other great ideas, after someone succeeds to do it it seems weird that nobody has tried to do such a thing before. However it is likely that the parameters of the process are very critical for obtaining a layer with good characteristics, so a large number of experiments have been necessary to determine them.
    - jpgvm 3y ago
      Oh wow! I guess I have a new rabbit hole to go down. Thanks for the info, I just presumed it would be MBE.
- adrian_b 3y ago
  For those who are not familiar with semiconductor technology, epitaxial growth is one of the most important technological processes that are used in it. Epitaxial growth means the deposition of a monocrystalline layer of some material over a substrate (i.e. a wafer) that is also a single crystal. Most methods of layer deposition create polycrystalline layers. In order to succeed to grow a monocrystalline layer it is necessary for the deposited material and the substrate material to be compatible in certain properties and the growth must be done in certain carefully controlled conditions. Many semiconductor materials can be used only if it is possible to grow them epitaxially, because either it is impossible to make big enough crystals by other methods, or the big crystals have various undesirable properties, for instance low thermal conductivity. The fact that the team from Georgia Tech, together with the Chinese team from Tianjin University, have achieved epitaxial growth of graphene over a substrate with excellent properties for semiconductor device fabrication, like silicon carbide, changes completely the prospects of using graphene in practical semiconductor devices.
adrian_b 3y ago
Free complete article: https://arxiv.org/abs/2308.12446 https://arxiv.org/abs/2308.12446

by tromp 3y ago

gilleain 3y ago

Side-quest : "what the heck is 'epigraphene'?": > Graphene’s original promise to succeed silicon faltered due to pervasive edge disorder in lithographically patterned deposited graphene and the lack of a new electronics paradigm. Here we demonstrate that the annealed edges in conventionally patterned graphene epitaxially grown on a silicon carbide substrate (epigraphene) are stabilized by the substrate and support a protected edge state. From https://www.nature.com/articles/s41467-022-34369-4 https://www.nature.com/articles/s41467-022-34369-4

jpgvm 3y ago
> epitaxially Is the keyword you are after. Basically this is a vapour deposition technique of some sort, almost certainly using MBE (molecular beam epitaxy) to grow the graphene on the silicon carbide substrate.
- adrian_b 3y ago
  While MBE is the best method for many kinds of materials, in this special case a completely different method has been used. Half of silicon carbide is carbon, and by heating silicon carbide at very high temperatures and low pressures the silicon atoms that are close to the surface evaporate, leaving a superficial layer made of carbon. By applying a certain thermal treatment, the carbon layer crystallizes into a layer of monocrystalline graphene. Like for many other great ideas, after someone succeeds to do it it seems weird that nobody has tried to do such a thing before. However it is likely that the parameters of the process are very critical for obtaining a layer with good characteristics, so a large number of experiments have been necessary to determine them.
  - jpgvm 3y ago
    Oh wow! I guess I have a new rabbit hole to go down. Thanks for the info, I just presumed it would be MBE.
adrian_b 3y ago
For those who are not familiar with semiconductor technology, epitaxial growth is one of the most important technological processes that are used in it. Epitaxial growth means the deposition of a monocrystalline layer of some material over a substrate (i.e. a wafer) that is also a single crystal. Most methods of layer deposition create polycrystalline layers. In order to succeed to grow a monocrystalline layer it is necessary for the deposited material and the substrate material to be compatible in certain properties and the growth must be done in certain carefully controlled conditions. Many semiconductor materials can be used only if it is possible to grow them epitaxially, because either it is impossible to make big enough crystals by other methods, or the big crystals have various undesirable properties, for instance low thermal conductivity. The fact that the team from Georgia Tech, together with the Chinese team from Tianjin University, have achieved epitaxial growth of graphene over a substrate with excellent properties for semiconductor device fabrication, like silicon carbide, changes completely the prospects of using graphene in practical semiconductor devices.

adrian_b 3y ago

Free complete article: https://arxiv.org/abs/2308.12446 https://arxiv.org/abs/2308.12446