What are semiconductors?
A semiconductor is a material (commonly a solid chemical element or compound) with distinct electrical properties: in some cases it will conduct electricity, but not in others. Thus, control of electrical current is enabled. A semiconductor’s conductance varies depending on the current or voltage applied to a control electrode, or on the intensity of irradiation by infrared (IR), visible light, ultraviolet (UV), or X rays.
Semiconductors can be found at the heart of modern electronics. Some examples include microprocessor chips and transistors, and virtually any device that is computerized or uses radio waves relies on semiconductors. Nowadays, the most commercially important semiconductor is silicon, although many others are also in use.
What is graphene?
Graphene is a one-atom-thick layer of carbon atoms arranged in a hexagonal lattice. It is the building-block of Graphite (which is used, among others things, in pencil tips), but graphene is a remarkable substance on its own - with a multitude of astonishing properties which repeatedly earn it the title "wonder material".
Graphene is the thinnest material known to man at one atom thick, and also incredibly strong - about 200 times stronger than steel. On top of that, graphene is an excellent conductor of heat and electricity and has interesting light absorption abilities. Graphene has potential to revolutionize many applications, among these are solar cells, batteries, sensors and more.
Graphene as a semiconductor
Semiconductors are defined by their band gap: the energy required to excite an electron stuck in the valence band, where it cannot conduct electricity, to the conduction band, where it can. The band gap needs to be large enough so that there is a clear contrast between a transistor’s on and off states, and so that it can process information without generating errors.
Among graphene's superlative properties is exceptional electrical conductivity. This property makes the material attractive for many applications, but it is problematic for use as a semiconductor. For that, graphene would need a bandgap (which it normally lacks), or in other words to behave not just as a conductor but to also have an insulator mode.
Scientists have found various methods to introduce a bandgap to graphene. By fabricating graphene in specific shapes (like ribbons), by using certain growth methods paired with specific materials, by using graphene's morphological structure (namely wrinkles), by doping the material and more. Other 2D materials can be used instead or together with graphene, that have an inherent bandgap. These materials may prove to be an easier path towards next-gen semiconductor based devices.
The latest graphene semiconductor news:
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.
A technique for growing graphene nanoribbons on semiconductors may lead to more efficient electronics
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.