Spain Leads the Way in Leveraging 2-D Materials for Optoelectronics
We speak to leaders from two of the key organizations leading this work—one from academia and another from business—to see what is creating this innovation ecosystem
Spain is at the center of research that is trying to revolutionize the way in which integrated circuits (ICs) operate. ICs are, of course, used in nearly every electronic device we have today. But despite revolutionizing our world, they depend on relatively slow moving electrons for processing.
The dream has been to devise a new paradigm for processing that replaces electrons with photons that are capable of traveling at the speed of light. The problem has been that these so-called photonic circuits were just too large to be functional because of their need to accommodate different wavelengths of light.
This is where the Institute of Photonic Sciences (ICFO) in Barcelona and the CIC nanoGUNE in San Sebastian often in conjunction with the company Graphenea S.L. also based in San Sebastian have taken on bold research that leverages the capability of two-dimensional (2-D) materials to compress the wavelengths so that they operate in much smaller dimensions.
We have seen this collaboration in full effect last year when these three institutions collaborated in the development of an optical antenna made from graphene that can capture infrared light and transform it into graphene plasmons, which are collective oscillations of free electron gas density. This research, which we covered in our July 2014 Graphene Council newsletter, was seen as being an essential step in graphene plasmonic circuits.
We have also seen different combinations of this collaboration tackle photovoltaics in which graphene was employed in the conversion and the conduction layers of a photovoltaic cell.
In research described in January of this year, ICFO and CIC nanoGUNE discovered, somewhat surprisingly, that the combination of graphene sandwiched between two films of hexagonal boron nitride is an excellent host for extremely strongly confined light. This latest research is expected to open up new opportunities for applications of 2-D materials and make signal processing and computing much faster, and optical sensing more efficient.
With all this activity, for our Q&A this quarter, we have spoken with representatives from two of these organizations: Jesus de la Fuente, CEO of Graphenea and Frank Koppens, Professor and Group Leader at ICFO.
Q. The research for optoelectronic applications for graphene and other 2-D materials were initially a little slower to develop than those in electronics. What attracted you and your colleagues at Institute of Photonic Sciences (ICFO) to investigate the world of 2-D materials for optoelectronics?
The community that initially studied graphene focused more on its transport and conduction properties as these stood out mostly. But after that, it was quickly recognized that the absence of a bandgap might even have more advantages for the optoelectronic properties: It’s an extreme broadband absorber, enabling photodetection for visible, infrared and terahertz frequencies. Moreover, the photoresponse speed is very high. In addition, methods were found to make the photosensivity much higher by combining the graphene with other nano materials.
Q. The ICFO has been hotly pursuing the potential of 2-D materials in photovoltaics as well as creating photonic circuits that duplicate the operation of integrated circuits. Could you discuss the strengths and witnesses of these two application areas for 2-D materials and how you see each progressing in the near future, i.e. do you see what application being closer to realization than the other?
Graphene is an excellent material for photonic circuits, and its integration with silicon photonics has partially already been shown in lab demonstrations, for example, ultra-fast optical modulators and detectors. These components could potentially be operated with a much smaller footprint, lower power consumption and with higher speed than what is possible with current technologies. As there is already great interest from industry in this direction, and the initial prototypes have already demonstrated very good performance, I expect fast development for the future. In particular, graphene can, in principle, be integrated (monolithically) with silicon technologies, so I expect that soon large-scale integration of this technology will be shown.
Regarding photovoltaics, see my comments below.
Q. You and your colleagues at ICFO have been leaders at showing that 2-D materials can be used in photovoltaics to create what is termed “hot carrier” cells in which one photon can be converted into multiple electrons, leading to high energy conversion efficiency for solar cells that could eclipse the Shockley-Quisser limit of 32 percent. What are both the scientific and engineering obstacles that still need to be overcome to make these “hot carrier” cells commercially available?
There are still big challenges to overcome in order to harvest the power from graphene hot electrons. Even though the hot carrier generation is very efficient, it still has to be shown that the energy extraction is sufficiently efficient in order to compete with existing technologies. There are several directions possible, i.e. combining graphene with semiconductors or heterostructures of graphene and 2D insulators. These are currently being tested.
Q. Turning back to photonic circuits, what do think is the realistic potential for these circuits reaching the dimensions of ICs and what scientific and engineering obstacles need to overcome to make that potential a reality?
The potential is in data transfer inside microchips, as well as between microchips. In addition, it can be used for data transfer in data centers. In principle the dimensions of ICs have been reached already but there are quite some engineering challenges in order to make the production technology worked at the required size. Also, the design of the individual components is further being perfected.
Q. What is currently on the agenda for ICFO and yourself in using 2-D materials for photonic circuits and photovoltaics?
We are working on several types of highly sensitive photodetectors, based on graphene, 2D materials and semiconductor nanomaterials. By combining these materials, very sensitive detectors can be made that work for visible and infrared. In addition, this optical sensing technology can be made flexible and semi-transparent. You can think of many applications: multi-spectral imaging for night vision or medical applications, as well as wearable functionalities.
Currently, we are strongly improving the technology readiness towards these applications.
Q. Are you pursuing anything outside of photonic circuits and photovoltaics with 2-D materials?
We are also interested in mid-infrared detectors and plasmonics. Here, the performance is very high and graphene has many unique advantages. For example it’s possible to tune the detection frequency with the application of voltage. And the optical field compression due to plasmonic effects is more than a million. These capabilities could lead to better sensors for mid-infrared wavelengths (e.g. bio-sensing) or detectors that can identify specific materials or gases.
Q. First, could you please provide a little background of how Graphenea came to be, what your business model is and what you aim to achieve in the business of graphene, i.e. a producer of devices based on graphene or a producer of graphene?
Graphenea is a leading graphene producer and we are focused in the graphene synthesis of CVD graphene and Graphene Oxide. Our business model is to produce and commercialize custom graphene materials for industrial applications.
Q. The research for optoelectronic applications for graphene and other 2-D materials were initially a little slower to develop than those in electronics. In your latest work with ICFO and CIC nanoGUNE you have been pushing the potential of 2-D materials for optoelectronics. What attracted Graphena to work with these institutions in the development of 2-D materials for optoelectronics?
We are glad to work with two leading institutions in the optoelectronics field as ICFO and CIC nanoGUNE. Our strategy is to partner with the leaders technology developers in each specific application supplying the specific graphene materials needed.
Q. Graphenea has also been working with these institutions mentioned above in exploiting the potential of 2-D materials in photovoltaics as well as creating photonic circuits that duplicate the operation of integrated circuits. Could you discuss the strengths and witnesses of these two application areas for 2-D materials and how you see each progressing in the near future, i.e. do you see what application being closer to realization than the other?
Photovoltaic and Photonics are very interesting future applications but a lot of research, development and pre-production work must be done before we will see them in the market. We expect to see graphene-enhanced photosensors and biosensors to hit niche market segments in the mid-term.
Q. What is currently on the agenda for Graphenea in applying graphene and other 2-D materials outside of optoelectronic applications? Could you please discuss those other fields and your projects within them?
Our mission is to develop high quality, cost-competitive graphene materials to the research community and industrial companies. Our roadmap plans to increased production capacity and wafer size and our R&D team is working in the development of specific graphene materials for industrial applications in joint-development projects.