Phosphorene: competitor to graphene as a future silicon substitute?
Graphene, the material which forms layers of carbon atoms only one atom thick carbon, had a spectacular rise to fame as the subject of a 2010 Nobel Prize. However, similar thin-layer structures can also be formed by black phosphorous. Chemists at the Technical University of Munich (TUM) have developed a semiconducting material in which individual phosphorus atoms are replaced by arsenic. In a collaborative international effort, American colleagues have built the first field-effect transistors from the new material.
Continued scaling implies, say the TUM researchers, that the size of silicon transistors is reaching its physical limit. At the same time, consumers would like to have flexible devices, devices that can be incorporated into clothing and other wearables. Such considerations have stimulated a search for new materials that might one day replace silicon.
Black arsenic phosphorus might be such a material. Like graphene, which consists of a single layer of carbon atoms, it forms extremely thin layers. The array of possible applications ranges from transistors and sensors to mechanically flexible semiconductor devices. Unlike graphene, whose electronic properties are similar to those of metals, black arsenic phosphorus [natively] behaves like a semiconductor.
A cooperation between the Technical University of Munich and the University of Regensburg on the German side, and the University of Southern California (USC) and Yale University in the United States has now, for the first time, produced a field effect transistor made of black arsenic phosphorus.
The compounds were synthesised by Marianne Koepf at the laboratory of the research group for Synthesis and Characterisation of Innovative Materials at the TUM. The field effect transistors were built and characterised by a group headed by Professor Zhou and Dr. Liu at the Department of Electrical Engineering at USC.
The new technology developed at TUM allows the synthesis of black arsenic phosphorus without high pressure. This requires less energy and is cheaper. The gap between valence and conduction bands can be precisely tuned by adjusting the arsenic concentration. "This allows us to produce materials with previously unattainable electronic and optical properties in an energy window that was hitherto inaccessible," says Professor Tom Nilges, head of the research group for Synthesis and Characterization of Innovative Materials.
With an arsenic concentration of 83% the material exhibits an extremely small band gap of only 0.15 electron volts (eV), making it a likely candidate for sensors which can detect long wavelength infrared radiation. LiDAR (Light Detection and Ranging) sensors operate in this wavelength range, for example. They are used, among other things, as distance sensors in cars; other applications include measurement of dust particles and trace gases in environmental monitoring.
A further aspect of these new, two-dimensional semiconductors is their anisotropic electronic and optical behaviour. The material exhibits different characteristics along the x- and y-axes in the same plane. To produce graphene-like films the material can be peeled off in ultra thin layers: the thinnest films obtained so far are only two atomic layers thick.
The work has been formally published as;
“Black Arsenic–Phosphorus: Layered Anisotropic Infrared Semiconductors with Highly Tunable Compositions and Properties”
Bilu Liu, Marianne Köpf, Ahmad N. Abbas, Xiaomu Wang, Qiushi Guo, Yichen Jia, Fengnian Xia, Richard Weihrich, Frederik Bachhuber, Florian Pielnhofer, Han Wang, Rohan Dhall, Stephen B. Cronin, Mingyuan Ge, Xin Fang, Tom Nilges, Chongwu Zhou
Adv. Mater., 2015, Early View – DOI: 10.1002/adma.201501758
https://onlinelibrary.wiley.com/wol1/doi/10.1002/adma.201501758/abstract
Technical University of Munich; www.acinnomat.ch.tum.de
If you enjoyed this article, you will like the following ones: don't miss them by subscribing to :
