Advanced Semiconductor Laboratory
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Ronghui Lin

August 26, 2016 - Posted in Discussion
​Graphene is a peculiar material that continuously attracts the attention of the science community. It has a unique two dimension structure in which each carbon atoms are connected with 3 neighboring carbon atoms with σ bonds, forming a series of hexagonal structures in the plane.  Some of the most attractive properties include ultra-high strength, high in plan thermal and current conductivity.
Nature has no shortage way to surprise us. As this equation indicates, (III+V)/2=IV, it seems we can arrange boron and nitrogen, which are carbon’s immediate neighbor, in a similar fashion and get a stable structure. It is hexagonal boron nitride (h-BN).  The structure of h-BN is shown as below, alternating B and N atoms form honeycomb layer, each layer is bonded by Van der Waal force. 
Fig.1 TEM images of few-layer h-BN [1]

h-BN has a  large band gap of 5-6.5eV, and it is direct bandgap in the DUV region, so it is a promising material for DUV led and DUV laser. Apart DUV devices, h-BN can also be used as neutron detector,

Fig.2 Lasing at 215nm excited by electron-beam[2]
Another interesting structure that formed by carbon is the carbon nanotube, it seems that h-BN can also be rolled up and form a nanotube.  There are many ways to fabricate h-BN nanotubes, including arc discharge[3], high temperature thermal annealing of h-BN powder[4], or by CVD[5].
Fig.3 BN nanotubes[6]
Because of the similarity between h-BN and graphene, some scientists suggest to make BN-C hybrid in plane hetero structure. Because both materials have layered structure, the hetero structure can be peeled off and be transferred to any other substrate.  The bandgap of graphene is zero, but by introducing little domains of BN, a bandgap can be opened in graphene, and the bandgap is dependent on BN concentration. 
figure4 process.png
Fig.4 In-plane hetero structures of graphene and hexagonal boron nitride [7]
The lattice constants between h-BN and graphene are very similar, meaning they can be stacked upon each other without introducing much stress. Zheng Liu et al. deposited a layer of graphene by CVD, then went on to deposit BN on top of graphene and obtained good film quality [8].  From this point of view, they are perfect substrate for the growth of each other. 
In a word, h-BN is an interesting material, people are just beginning to understand its amazing properties. I am sure in the future, people will find even more mind boggling applications of this material.
1. Nag, A., et al., Graphene Analogues of BN: Novel Synthesis and Properties. Acs Nano, 2010. 4(3): p. 1539-1544.
2. Watanabe, K., T. Taniguchi, and H. Kanda, Direct-bandgap properties and evidence for ultraviolet lasing of hexagonal boron nitride single crystal. Nature Materials, 2004. 3(6): p. 404-409.
3. Loiseau, A., et al., Boron nitride nanotubes with reduced numbers of layers synthesized by arc discharge. Physical Review Letters, 1996. 76(25): p. 4737-4740.
4. Chen, Y., et al., A solid-state process for formation of boron nitride nanotubes. Applied Physics Letters, 1999. 74(20): p. 2960-2962.
5. Pakdel, A., et al., A comprehensive analysis of the CVD growth of boron nitride nanotubes. Nanotechnology, 2012. 23(21).
6. Zhi, C.Y., et al., Effective precursor for high yield synthesis of pure BN nanotubes. Solid State Communications, 2005. 135(1-2): p. 67-70.
7. Liu, Z., et al., In-plane heterostructures of graphene and hexagonal boron nitride with controlled domain sizes. Nature Nanotechnology, 2013. 8(2): p. 119-124.
8. Liu, Z., et al., Direct Growth of Graphene/Hexagonal Boron Nitride Stacked Layers. Nano Letters, 2011. 11(5): p. 2032-2037.

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August 29, 2016 at 7:57 PM
Very interesting article!