Phosphorene: competitor to graphene as a future silicon substitute?

July 10, 2015 // By Graham Prophet
Graphene – the physical state of carbon in which it forms single-atom-thickness layers – continues to be the subject of a great deal of research work, both for its physical properties and the prospect of fabricating future electronic devices in the material. Researchers at the Technical University of Munich have been exploring another exotic material; layered semiconducting black arsenic phosphorus - as an alternative to silicon.

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