Finding Semicon: Optoelectronics made easy with Triazine-based graphitic carbon nitride

Researchers have explored a new material in the carbon-nitride family. Triazine-based graphitic carbon nitride (TGCN) is a semiconductor that should be highly suitable for applications in optoelectronics.

A new material from the carbon-nitride family has been explored by research scientists from Humboldt – Universität and the Helmholtz-Zentrum Berlin. Triazine-based graphitic carbon nitride (TGCN) is a semiconductor, which is highly-suitable for applications in optoelectronics. Its structure is two-dimensional and reminiscent of graphene. Unlike graphene, however, the conductivity in the direction perpendicular to its 2D planes is 65 times higher than along the planes themselves.

Like silicon semiconductors, some organic materials can also be used in optoelectronics. Whether in solar cells, light-emitting diodes, or in transistors, what is important is the band gap, i.e. the difference in energy level between electrons in the valence band (bound state) and the conduction band (mobile state).

Charge carriers can be raised from the valence band into the conduction band by means of light or an electrical voltage. This is the principle behind how all electronic components operate. Band gaps of one to two electron volts are ideal.

A team headed by chemist Dr. Michael J. Bojdys at Humboldt University Berlin recently synthesised a new organic semiconductor material in the carbon-nitride family. Triazine-based graphitic carbon nitride (or TGCN) consists of only carbon and nitrogen atoms, and can be grown as a brown film on a quartz substrate. The combination of C and N atoms form hexagonal honeycombs similar to graphene, which consists of pure carbon.

Just as with graphene, the crystalline structure of TGCN is two-dimensional. With graphene, however, the planar conductivity is excellent, while its perpendicular conductivity is very poor. In TGCN it is exactly the opposite: the perpendicular conductivity is about 65 times greater than the planar conductivity. With a band gap of 1.7 electron volts, TGCN is a good candidate for applications in optoelectronics.

“TGCN is therefore the best candidate so far for replacing common inorganic semiconductors like silicon and their crucial dopants, some of which are rare elements,” says Bojdys. “The fabrication process we developed in my group at Humboldt-Universität, produces flat layers of semiconducting TGCN on an insulating quartz substrate. This facilitates upscaling and simple fabrication of electronic devices.”

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