IBM Research: Growing single-crystalline materials on reusable graphene

Dr. Jeehwan Kim

Since the first demonstrations of removing graphene from graphite a decade ago, the size of a single-oriented piece has been limited to less than a millimeter – far too small for real-world application. Our team worked to break through the original millimeter barrier, and together we found success in producing wafer-scale, single-crystalline sheets of graphene 100 millimeters (four inches) in diameter. Having achieved scalability, we reported the possibility of replacing a thick, “single-crystalline” wafer with a single-atom-thick graphene layer for growing single-crystalline materials in the paper, “Principle of direct van der Waals epitaxy of single-crystalline films onepitaxial graphene” – published today with my chief collaborator Dr. Can Bayram in Nature Communications.

Graphene holds incredible promise as a linchpin material for breakthroughs in numerous technologies, and my team at IBM’s Thomas J. Watson Research Center is working to make its potential a reality. Due to its incredible strength and supreme electrical, optical and mechanical properties, graphene – pure carbon functional at the thickness of one atom – has been touted as the next big thing in everything from high-frequency transistors and photo-detectors, to flexible electronics and biosensors. IBM is investing $3B over the next five years towards initiatives such as this, which are building a bridge to a “post-silicon” era.

Part of what makes the material so promising is its strength relative to thickness. At only .3 to .4 nanometers thick (that’s 60,000 times thinner than a sheet of plastic wrap, or 1,000,000 times thinner than a strand of human hair), graphene is an astonishing 200 times stronger than steel. It is also the world’s most conductive material yet discovered, extraordinarily flexible and – as a single layer of carbon atoms – the first two-dimensional material.

Our groundbreaking approach, known as “graphene-based growth/transfer,” allows single-crystalline semiconductor film growth on graphene – rather than on expensive, single-crystalline wafers. The graphene serves as a “seed” for single-crystalline film growth, and because this film can be separated precisely from the graphene surface, the graphene can be reused for further growth. In principle, graphene has therefore been demonstrated as an infinitive source for growing these semiconductor materials, making the work an enormously cost-effective and reliable production method for single-crystalline films.

Graphene’s periodic hexagonal crystal structure then allowed us to experiment with growing other semiconductor materials that demonstrate similar structural properties. Previously, production of single-crystalline semiconductor films required the use of ~1 millimeter-thick, single-crystalline wafer templates that were not reusable and were very expensive. For example, growth of a 4-inch, wafer-scale GaN (gallium nitride, a direct bandgap semiconductor) film would require a 4-inch SiC wafer – at the cost of some $3000. Now, graphene can be produced in a lab to replace the expensive SiC wafer.

Furthermore, the new growth technique is useful in that semiconductor devices can be deposited on graphene and released or transferred to a flexible substrate.

While we have demonstrated an important, present-day use for this material, the future of graphene as a standalone material is still bright. Uses for graphene are being developed for a number of electronics, and over the next five years, the material could be used as transparent electrodes for touch screen devices, rollable e-paper and foldable LEDs. In the near future, uses are being developed for large-area graphene in high-frequency transistors, logic transistors/thin-film transistors and beyond. Its high electronic mobility – the ability of charged particles to move through a medium in response to an electronic field – makes graphene a promising material.