Graphene Semiconductors: Introduction and Market status - Page 2

Researchers at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) have developed a way to assemble transistors based on graphene and molybdenum disulfide.

The method etches narrow channels in conducting graphene laid down on a silicon-dioxide substrate. These channels are then filled with the 2D MoS₂. The method allows graphene to inject electrons into the conduction band of the MoS2 channel with improved performance compared with simply using metal contacts to inject electrons, according to the researchers.

Fuji Pigment recently announced the development of a large-scale manufacturing process for carbon and graphene quantum dots (QDs). QDs are usually made of semiconductor materials that are expensive and toxic, especially Cd, Se, and Pb. Fuji Pigment stated that its toxic-metal-free QDs exhibit a high light-emitting quantum efficiency and stability comparable to the toxic metal-based quantum dots.

Quantum yield of the carbon QDs currently exceeds 45%, and the company said it is still pursuing higher quantum efficiency. Quantum yield of the graphene quantum dot is over 80%. QD’s ability to precisely convert and tune a spectrum of light makes them ideal for TV displays, smartphones, tablet displays, LEDs, medical experimental imaging, bioimaging, solar cells, security tags, quantum dot lasers, photonic crystal materials, transistors, thermoelectric materials, various type of sensors and quantum dot computers.

Researchers at Japan's RIKEN have discovered that wrinkles in graphene can restrict the motion of electrons to one dimension, forming a junction-like structure that changes from zero-gap conductor to semiconductor back to zero-gap conductor. Moreover, they have used the tip of a scanning tunneling microscope to manipulate the formation of wrinkles, opening the way to the construction of graphene semiconductors by manipulating the carbon structure itself in a form of "graphene engineering."

The scientists were able to image the tiny wrinkles using scanning tunneling microscopy, and discovered that there were band gap openings within them, indicating that the wrinkles could act as semiconductors. Two possibilities were Initially considered for the emergence of this band gap. One is that the mechanical strain could cause a magnetic phenomenon, but the scientists ruled this out, and concluded that the phenomenon was caused by the confinement of electrons in a single dimension due to "quantum confinement."

A few weeks ago we reported on a new IDTechEx market report, in which they predict that the graphene market will reach nearly $200 million by 2026, with the estimation that the largest sectors will be composites, energy applications and graphene coatings.

We were very interested in learning more, and Dr Khasha Ghaffarzadeh, IDTechEx's head of consulting was kind enough to answer a few questions and explain the company's view on the graphene market.

Q: IDTechEx has been following graphene for a long time with dedicated events and reports. Why is this new material interesting for IDTechEx?

We have a long track record of analyzing emerging advanced materials such as quantum dots, CNTs, Ag nanostructures, silicon nanostructures, OLED materials, etc. We were however pulled into the world of graphene by our clients’ questions. Once in, we soon realized that there is a big synergy between graphene and our events. in fact, our events on supercapacitors and printed electronics were the right near-term addressable market for graphene, and that is why we managed to rapidly build up the largest business-focused event on graphene. Our events on graphene are held in the USA and Europe each year see www.IDTechEx.com/usa.

Scientists at the University of Basel have managed to synthesize boron-doped graphene nanoribbons and characterize their structural, electronic and chemical properties. The modified material could potentially be used as a sensor for ecologically damaging nitrogen oxides.

Altering graphene sheets to nanoribbon shape is known as a way of inducing a bandgap, whose value is dependent on the width of the shape. To tune the band gap in order for the graphene nanoribbons to act like a silicon semiconductor, the ribbons usually undergo doping. That means the researchers intentionally introduce impurities into pure material for the purpose of modulating its electrical properties. While nitrogen doping has been realized, boron-doping has remained unexplored. Subsequently, the electronic and chemical properties have stayed unclear thus far.

Researchers at the University of Wisconsin-Madison have discovered a way of growing graphene nanoribbons with desirable semiconducting properties directly on a conventional germanium semiconductor wafer. This finding may allow manufacturers to easily use graphene nanoribbons in hybrid integrated circuits, which promise to deliver a major boost to the performance of next-gen electronic devices. This technology could also have specific uses in industrial and military applications, such as sensors that detect specific chemical and biological species and photonic devices that manipulate light.

The technique for producing graphene nanoribbons is said to be scalable and compatible with the prevailing infrastructure used in semiconductor processing - nanoribbons that can be grown directly on the surface of a semiconductor like germanium are more compatible with planar processing used in the semiconductor industry, and so would pose less of a barrier to integrating these materials into electronics in the future.

Researchers from Korea University have developed a simple and microelectronics-compatible method to grow graphene and have declared the successful synthesis of wafer-scale (four inches in diameter), high-quality, multi-layer graphene on silicon substrates. The method is based on an ion implantation technique, a process in which ions are accelerated under an electrical field and smashed into a semiconductor. The impacting ions change the physical, chemical or electrical properties of the semiconductor.

Ion implantation is a technique normally used to introduce impurities into semiconductors. In the process, carbon ions were accelerated under an electrical field and bombarded onto a layered surface made of nickel, silicon dioxide and silicon at the temperature of 500 degrees Celsius. The nickel layer, with high carbon solubility, is used as a catalyst for graphene synthesis. The process is then followed by high temperature activation annealing (about 600 to 900 degrees Celsius) to form a honeycomb lattice of carbon atoms, a typical microscopic structure of graphene.

Scientists from Ulsan National Institute of Science and Technology (UNIST) and Pohang University of Science and Technology in South Korea synthesised nitrogenated 2D crystals using a simple chemical reaction in liquid phase.

Introducing foreign elements (there are not carbon) into graphene's carbon lattice structure is a known way of developing other 2D crystals. Nitrogen has a suitable atomic size and structure to fit into a strong network of carbon atoms, by creating bonds in which electrons are shared by the whole network.

A team of researchers from the University of Pennsylvania, University of California and University of Illinois at Urbana-Champaign has demonstrated a way to change the amount of electrons that reside in a given region within a piece of graphene and have a proof-of-principle in making the fundamental building blocks of semiconductor devices using the 2D material. Their method enables this value to be tuned through the application of an electric field, which means that graphene circuits made in this way could theoretically be manipulated without physically altering the device.

Chemically doping graphene to achieve p- and n-type version of the material (similar to traditional circuits) is possible, but it comes at the price of sacrificing some of its unique electrical properties. A similar effect is possible by applying local voltage changes to the material, but manufacturing and placing the necessary electrodes is complicated. The team of researchers claims it has now come up with a non-destructive, reversible way of doping, that doesn’t involve any physical changes to the graphene.

A joint research team of Korean scientists from the Korea Research Institute of Standards and Science (KRISS) and Hungarian scientists from the Center of Natural Sciences developed a new way of producing graphene nanoribbons, to be used as a semiconductor element. The graphene nanoribbon is between 2 to 10 nm in size with edge frame form that can be controlled at room temperature. Its production was achieved by using a technology called scanning tunneling lithography (STL), where the scientists succeeded in cutting the shape of the nanoribbon edge as they wished.

In addition, the research team discovered a phase transition phenomenon changing the graphene nanoribbon either to semiconductor or metal depending on increase or decrease in their width, which raised the possibility for its commercialization.