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:
A team of researchers from China and Japan has designed a new method to make minuscule ribbons of graphene that are highly sought-after building blocks for semiconductor devices thanks to their predicted electronic properties. These structures, however, have proven challenging to make.
Previous attempts at making graphene nanoribbons relied on placing sheets of graphene over a layer of silica and using atomic hydrogen to etch strips with zigzag edges, a process known as anisotropic etching. This method, however, only worked well to make ribbons that had two or more graphene layers. Irregularities in silica created by electronic peaks and valleys roughen its surface, so creating precise zigzag edges on graphene monolayers was a challenge.
Aixtron takes part in “HEA2D” project to investigate the production, qualities, and applications of 2D nanomaterials
Aixtron, a leading provider of deposition equipment, is working together with five partners in the “HEA2D” project to investigate the production, qualities, and applications of 2D nanomaterials.
The joint project is now researching an end-to-end processing chain consisting of various deposition processes for 2D materials, processes for transfer onto plastic foils, and mass integration into plastics components. AIXTRON’s partners for implementing systems technology and integrating materials into plastic molded parts are the Fraunhofer Institute for Production Technology (IPT), Coatema Coating Machinery, and Kunststoff-Institut Lüdenscheid (K.I.M.W.). This work is being supported in terms of nano-analytics and the development of prototype components by the Institutes of “Electronic Materials and Nanostructures” (University of Duisburg-Essen) and “Graphene-based Nanotechnology” (University of Siegen).
Graphene-Info is happy to introduce a new feature: Experts Roundup. We asked several graphene professionals to answer a graphene related question. We hope this will prove to be an interesting read and can help shed light on the nooks and cranks of the graphene industry. Enjoy!
Do you think CVD will ever be a viable way to mass produce commercial graphene sheets?
Gonçalo Gonçalves, product marketing specialist, Aixtron: Chemical vapour deposition has been used for several decades in the semiconductor industry to deposit high-quality thin-films. This technique is known to provide superior process reliability and throughput which are key requirements in the manufacturing of integrated circuits. Since 2004, graphene has emerged as a “wonder material” with an impressive number of potential applications across several fields. The discovery of a CVD route to produce graphene has also been an important achievement towards the integration of this carbon nanomaterial into semiconductor devices. With the advance of the graphene field from basic to applied research new and more complex challenges arise, especially in the integration reliability. CVD technique will find its way to mass production of graphene once these challenges are addressed and the benefits of graphene in semiconductor devices are unveiled.
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.