Jie Sun, Niclas Lindvall, August Yurgens, Mikroteknologi och Nanovetenskap, Chalmers Tekniska Högskola AB, Göteborg 41296, Sweden
 

Graphene is traditionally prepared by exfoliation of graphite, and to fabricate large area single layer graphene is challenging. Chemical vapor deposition (CVD) of graphene on metals is recently developed for this purpose. Since 2009, we in Chalmers have grown single layer graphene on metal foils (Cu, Pt, Ta, etc.), or evaporated metallic thin films on silicon.1-9 The graphene is grown in a cold-wall Aixtron system with CH4/C2H2. The graphene can be transferred onto other substrates such as SiO2/Si by wet chemically etching away the copper catalyst or, more environmentally friendly, by electrochemical bubbling delamination.10 The carrier mobility for electrons and holes is about 3000 cm2/(Vs), measured through both the field effect and the Hall effect. Some devices show mobilities ~5000 cm2/(Vs).

We also grow graphene directly on insulators without metal catalysts in CVD.1-9 The graphene is nanocrystalline, large area and uniform. Despite the lower mobility (40 cm2/(Vs)) compared to catalyzed graphene, its transparency (97%) and conductivity (1-a few kΩ/□ without intentional doping) is similar to standard graphene, making such transfer-free graphene very promising in applications of transparent electronics and molecular electronics. The graphene can be grown on arbitrary dielectrics that withstand high temperature. We have proposed a novel noncatalytic CVD (as opposed to catalytic graphene CVD on metals) mechanism to explain our experimental findings.3 Both the catalyzed and noncatalyzed graphene can be suspended, promising for nanoelectromechanical systems (NEMS).7,8

The graphene finds its applications in GaN optoelectronics. GaN compounds are widely used in light emitting diodes (LEDs) covering the spectrum from yellow to ultraviolet. We first study ordered and dense GaN light emitting nanorods with graphene grown by CVD as suspended transparent electrodes.11 As the substitute of indium tin oxide (ITO), the graphene avoids complex processing to fill up the gaps between nanorods and subsequent surface flattening and offers high conductivity to improve the carrier injection. The as fabricated devices have 32% improvement in light output power compared to conventional planar GaN-graphene diodes, mainly due to the much more enlarged light emitting areas.11

1. IEEE Transactions on Nanotechnology, 11 (2012) 255.
2. Applied Physics Letters, 98 (2011) 252107.
3. Applied Physics Letters, 100 (2012) 022102.
4. Journal of Applied Physics, 111 (2012) 044103.
5. Carbon, 50 (2012) 1987.
6. Advanced Materials, 24 (2012) 1576.
7. Proceedings of IEEE NEMS 2012, p. 11.
8. Proceedings of IEEE NEMS 2012, p. 19.
9. Nano Letters, 12 (2012) 5074.
10. Applied Physics Letters, 102 (2013) 022101.
11. Applied Physics Letters, 103, (2013) 222105.

Jie Sun got his PhD degree from Solid State Physics Division, Lund University. His major is semiconductor and carbon materials and devices. In particular, he focuses on III-V and Si semiconductors, high-k dielectrics, ballistic and quantum transport, and carbon electronics. Currently, he is responsible for CVD of graphene and its applications. He has published over 70 papers, of which more than 60 are covered by Web of Knowledge. He has an h-index of 12 (www.researcherid.com/rid/E-8239-2011). His current research directions include: 1. CVD of graphene using novel catalyst; 2. Noncatalytic CVD of graphene directly on dielectrics and semiconductors; 3. Eco-freindly electrochemical transfer of graphene by bubbling; 4. CVD of BN and MoS2; 5. Graphene transparent electrodes for GaN optoelectronics; 6. Graphene transparent electrodes for organic electronics; 7. Graphene sensors, graphene suspended channel devices; 8. Graphene, BN and MoS2 hybrid devices for classical and quantum transport.

Collaboration for joint projects is warmly welcome (e.g. EU and national funds application). Contacts: Jie.sun@chalmers.se