Since 2004, two physicists at the University of Manchester in the United Kingdom have separated graphene from graphite for the first time, this magical material has become a revolutionary material in many fields due to its excellent optical, electrical and mechanical properties.Especially in the field of microelectronics, graphene is considered to be the key to moving humanity from the "silicon age" to the "carbon age."
However, to achieve this step is not easy, there are many key technical obstacles that must be overcome, graphene's "zero band gap" characteristics are one of them.
Recently, Ma Lei's team, a professor at Tianjin Nanoparticles and Nanosystems International Research Center at Tianjin University, published a paper in the journal Nature to announce the final solution of this problem.
'Zero-bandgap' hinders humanity from entering 'carbon age'
As the first two-dimensional material found to exist stably at room temperature, graphene has unique electronic properties due to its unique arrangement of carbon atoms.
In an interview with China Science Journal, Mare said graphene has an extremely high mobility of electrons because of its unique band structure, which means electrons can move quickly.For example, a typical suspended graphene has mobility of up to 200,000 cm2V-1s-1, while single crystal silicon has mobility of only 1,000 cm2V-1s-1.This high electron mobility means higher operating efficiency and speed.
In addition to high mobility, graphene devices are also characterized by high integration and low power consumption as two-dimensional materials.These characteristics make graphene material is expected to become the core material of mankind from the "silicon age" to the "carbon age".
However, it is due to the characteristics of "zero bandgap" that graphene is still not currently available for large-scale digital circuit manufacturing.
The so-called band gap is the gap between the two energy bands.The existence of band gap is the key to achieving good switching ratio.In this way, the current can be effectively controlled to open or close.
From this perspective, the "band gap" can be likened to a "switch" mounted on graphene.When this "switch" is in place, graphene exhibits semiconductor properties and thus effectively completes digital circuit functions.However, without this "switch," graphene would remain "open" and exhibit metallic properties, making it impossible to use in the manufacture of digital circuit devices.
Unfortunately, although various types of graphene have been successfully prepared, none of them currently have both high mobility and bandgap graphene.Therefore, the search for high mobility graphene with this "switch" function has become a key challenge to solve the problem of graphene application in the field of microelectronics.
The "needle" found.
The approach of the Tianjin University Mare team to solve this problem does not sound complicated.
"Simply put, we select different silicon carbide crystal surfaces as substrates on which graphene can 'grow', and in the process precisely regulate the temperature, time and gas flow conditions of the graphene growth environment." said Marley.
He said that graphene, as a single layer of atomic structure, is very sensitive to external changes.Therefore, the "substrate" of its growth is different, which will lead to different properties of graphene.But that's why finding graphene that meets researchers' expectations is so challenging that it's like fishing for a needle in a haystack.
Fortunately, this "needle" was eventually found by the Mare team.
The semiconductor graphene developed by the team has a band gap of about 0.6 electron volts (eV) and room temperature mobility of up to 5,500 cm2V-1s-1, superior to at least one order of magnitude of all known two-dimensional semiconductors.
It is introduced that a circuit used to achieve basic logical relationships, usually composed of "zero" and "one" two states.However, in order to ensure the normal transmission and operation of digital information, it is necessary to clearly distinguish between the two states.If the difference between 'zero' and 'one' is not obvious, digital information is easily confused.To this end, scientists refer to the "switch ratio" to measure "zero" and "one", and the larger the value of the switch ratio, the higher the distinction between "zero" and "one", the lower the likelihood of confusion.
The team members said that previously, graphene nanorbands with bandgap have been obtained through chemical synthesis, but the graphene obtained in this way is difficult to use in device manufacturing and does not have the high mobility of semiconductor graphene.
"Overall, the properties of this material can be adapted to the needs of current industrial applications.In particular, its electron mobility at room temperature can reach 10 times that of silicon materials, so it is expected to show excellent performance in the application of electronic devices." said Marley.
In addition, the semi-balanced annealing method was used to prepare the semiconductor graphene, which has large growth area, high uniformity, simple process and low cost.
Let the "boat" grow into a "big carrier"
Silicon has long been the core material of modern electronics.However, with the rapid growth of people's demand for computing power and the tightening of the space for silicon electronics performance improvement, it is slowly recognized that the development of silicon materials has approached its physical limit.
Some point out that Moore's Law, which is the golden rule in the development of information, is gradually losing its guiding role.In this context, the birth of semiconductor graphene undoubtedly brought a new dawn to the entire semiconductor industry.
At present, the Tianjin University team is working to achieve a larger goal – to quickly achieve a technological leap from millimeter-level single crystal to inch-level single crystal semiconductor epitaxial graphene wafers.
"If we can produce an inch-sized single crystal semiconductor graphene wafer, these materials can be used directly to enable the manufacture of carbon-based integrated circuits."Mare said that this goal is not easy to achieve, like the evolution of a small sailing ship into a large aircraft carrier.Once this goal is achieved, mankind is expected to enter the era of carbon-based electronics.

"The first computer was large enough to fill the room, but it didn't even have the capabilities of a simple calculator; the '386' and '486' desktop computers of the 1990s were far faster than even the lowest-end laptops.At present, with the gradual emergence of semiconductor graphene on the stage of the next generation of integrated circuit manufacturing, future laptops are expected to greatly surpass today's high-performance computers in computing speed.The team said they are doing their best to speed up the process.