[HN Gopher] Researchers Create First Functional Semiconductor Ma...
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Researchers Create First Functional Semiconductor Made from
Graphene
Author : elorant
Score : 79 points
Date : 2024-01-05 13:23 UTC (9 hours ago)
(HTM) web link (research.gatech.edu)
(TXT) w3m dump (research.gatech.edu)
| ethbr1 wrote:
| Direct link to Nature:
| https://www.nature.com/articles/s41586-023-06811-0
|
| (Edit) Arxiv: https://arxiv.org/abs/2308.12446 (thanks adrian_b!)
| tromp wrote:
| 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 wrote:
| 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
| jpgvm wrote:
| > 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 wrote:
| 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 wrote:
| 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 wrote:
| 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 wrote:
| Free complete article:
|
| https://arxiv.org/abs/2308.12446
| bloopernova wrote:
| I am having trouble understanding the paper, have the researchers
| created "just" a single transistor, or have they created circuits
| containing transistors/diodes/capacitors/resistors?
|
| 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.
| marcosdumay wrote:
| They created a functional semiconducting wafer.
|
| Except that (AFAIK) nobody knows how to add metal to it. But
| one can use it to make transistors.
| adrian_b wrote:
| For electrical contacts, they have deposited chromium on it,
| and gold over chromium.
|
| 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.
| adrian_b wrote:
| At least a few more years will be needed to find methods to
| make better electrical contacts and better methods for doping,
| but now it seems very likely that this is possible.
|
| 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.
| test6554 wrote:
| Which I assume, comes with lots of funding.
| throwaway4good wrote:
| Curious that this is a collaboration with a Chinese university
| giving the ongoing US-China tech war.
| adrian_b wrote:
| If you cannot beat them, you must join them.
|
| 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.
| obscurette wrote:
| It's not this or another. In autocratic systems you use
| whatever methods you can - you steal, you copy, you cheat,
| you buy, you do your own research and you invent. And it's
| not so much about policy, but about money. Soviets for
| example did all of that as well, but eventually run out of
| money for various reasons.
| dekhn wrote:
| Scientists frequently take a global view and work with people
| who are in countries that are ostensibly competitors or
| enemies. The collaborators here work at Tianjin University- a
| very well regarded engineering university which likely has some
| of the world's best material scientists.
|
| 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.
| peter_d_sherman wrote:
| Excellent article!
|
| >"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!
| jbaczuk wrote:
| > "It's like driving on a gravel road versus driving on a
| freeway," de Heer said. "It's more efficient, it doesn't heat up
| as much, and it allows for higher speeds so that the electrons
| can move faster."
|
| 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.
| dekhn wrote:
| I imagine they're not talking about changing the drift
| velocity, but the rate of information propagation through the
| EM wave: https://en.wikipedia.org/wiki/Speed_of_electricity
| versus https://en.wikipedia.org/wiki/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.
| foota wrote:
| Distance is a limiting factor for memory bandwidth and other
| long circuits, but I'm not sure a speed up of 2x is feasible?
| jesse9766 wrote:
| Latency is an issue even inside a transistor itself, something
| known as propagation delay. When you have a bunch of logic
| gates chained together the propagation delay increases and the
| chance for a race condition occurring also increases. The
| propagation delay of a logic gate is one of the limiting
| factors of the speed of a circuit.
|
| 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.
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