Researchers Create First Functional Semiconductor Made from Graphene
research.gatech.edu
research.gatech.edu
I don't mean to diminish their accomplishment, I'm just trying to get a sense of what scale this is at and whether it can be mass produced yet.
Except that (AFAIK) nobody knows how to add metal to it. But one can use it to make transistors.
That permitted measurements, but due to the low level of doping that could be achieved, the contacts behaved like Shottky diodes, not like ohmic contacts.
It is stated in the paper that one of the main targets for further research is to improve the quality of the electrical contacts.
Despite the low level of doping, the resistivities obtained for the doped graphene were good, due to the extremely high carrier mobilities.
Before having graphene as a monocrystalline semiconducting layer with good carrier mobilities and a good value for the bandgap, other materials, like molybdenum or tungsten disulfide, seemed much more likely candidates for replacing silicon a decade or more from now.
After this breakthrough, graphene moves in front, as the most promising candidate.
(Edit) Arxiv: https://arxiv.org/abs/2308.12446 (thanks adrian_b!)
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.
> 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.
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.
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.
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.
>"We were motivated by the hope of introducing three special properties of graphene into electronics," he said. "It's an extremely robust material, one that can handle very large currents, and can do so without heating up and falling apart."
It would be awesome if that could, one day, make it into chips and other consumer electronic devices!
Anyway, great article!
If we're talking about core semiconductor applications, other 2D materials which have much larger bandgaps than the 0.6 eV reported in the paper, are much more favorable (specifically from TMD sub family, MoS2 for NMOS and WS2/WSe2 for PMOS).
This has been needlessly hyped, like this video...https://www.youtube.com/watch?v=gWUX2OTqkEo&ab_channel=Georg...
Graphene is better off for twisted bilayer superconductors, but this is much further down the road: https://crommie.berkeley.edu/research/tlbg/
Does it allow for higher speeds? I thought resistance increases the number of collisions the electrons make with the molecules in the material, heating up the material, does it actually change the "speed of electricity"? If anything, I would think it might actually increase, similar to water in a smaller pipe (see current formula below). Either way, I don't know if this (possible) change in speed is in any way significant when it comes to computing.
I = NeAVd
Where Ne is the number of free/conduction electrons per unit volume, A is the cross sectional area of the wire, and Vd is is the drift velocity.
I don't know if increasing the speed of electricity has real implications for small circuits; I guess it could make a nearly factor of 2 difference for long copper wires, but we use fiber for long connections anyway, and speed of light in glass is higher than speed of electricity in copper.
Transistor gates act as capacitors in a way. This capacitance increases the delay between switching on/off. [1]
To lower this delay, we can shorten the transistor gate. We've hit a wall with how small we can shorten this length, and it is exceedingly difficult to make smaller gates without running into quantum effects.
Higher electron mobility means that the delay inside the gate is reduced, allowing faster circuits.
[1]http://ece-research.unm.edu/jimp/vlsi/slides/chap4_1.html Switching speed of MOS systems strongly dependent [on]: Parasitic capacitances associated with the MOS transistor. Interconnect capacitance of "wires". Resistance of transistors and wires.
In my opinion, the theory that I have seen expressed very frequently by US citizens on various Internet forums, during the last few years, that the Chinese progress mainly by copying US and Western technology, is dangerously delusional.
That theory was true a couple of decades ago, but it has stopped being true many years ago.
In the last few years, I have been frequently surprised when searching research papers about certain subjects to find many more innovative research papers coming from China than from USA.
They seem to have been much more willing to try to follow lines of research for which there is a high risk that they will not be successful. This policy results in a large number of useless research papers, but also in a decent number of advances over the state of the art.
Recent research in USA, at least what is published, seems very risk-averse, with only a few notorious counter examples, e.g. how SpaceX works.
To me the closest analog would be England and Germany between 1800 and 1920. The two countries were intense competitors in science/technology/engineering, and it was typically rare for scientists in one country to be fully aware of what was going on in the other. However, the Dutch, who are between the two countries, played a key role in identifying and translating important scientific ideas, such as advanced microscope technology and the underpinnings of quantum mechanics.
In short, many scientists are globalists, while the nations that house them are less so.