Arsenic Phosphorus (BAP): Could This be the Poison Pill for Graphene?

The straight answer to that is an unequivocal no. But black arsenic phosphorus (BAP) could provide an extremely interesting alternative when it comes to producing infinitesimally thin layers of atoms that could be used in transistors.

However, graphene has already shown some fantastic operating characteristics, and its latest advantage, that it can be used to cool electronics, is particularly interesting. The ever-increasing processing and density demands made of modern transistors means that heat dissipation is a constant design challenge. But more on that later. What about this arsenic stuff?

Semiconducting material developed in which individual phosphorus atoms are replaced by arsenic

Researchers at the Technical University of Munich (TUM) have now developed a semiconducting material in which individual phosphorus atoms are replaced by arsenic. As part of this study into the electronic potential of BAP, US researchers at the University of Southern California and Yale University and a team at the German University of Regensburg have, for the first time, produced a field effect transistor made of black arsenic phosphorus.

An important characteristic of this new technology is it allows the synthesis of black arsenic phosphorus without high pressure, and the gap between valence and conduction bands can be precisely tuned by adjusting the arsenic concentration.

With a concentration of just over 80%, the material exhibits an extremely small band gap of only 0.15 electron volts, making it well-suited for sensors which can detect long-wavelength infrared radiation. One example is Light Detection and Ranging sensors, which operate within that wavelength range. They have several applications, one of which is to act as distance sensors in automobiles.

In some respects, BAP is already showing operational characteristics that place it on the front row of the grid in the race to develop alternatives to conventional silicon-based components.

But graphene will not be easily outdone by this newcomer, and its flexibility could be a key element in its future success. There is a clearly established consumer trend towards having flexible electronics embedded in clothing or, in extreme cases, buried under the skin as part of flexible tattoos. Clearly, hard and brittle silicon technology would not apply in either of these apps.

There are already many applications for flexible electronics, and plenty of development work to fully exploit the potential of graphene in this area is continuing. For example, Plastic Logic and the Cambridge Graphene Centre have already demonstrated the world's first flexible display with graphene incorporated into the pixel backplane.

That, coupled with the earlier-mentioned ability to cool electronics, secures graphene's deserved position on the electronics roadmap.

Keeping it cool

In a recent graphene-related breakthrough, researchers at the Chalmers University of Technology developed a method for efficiently cooling electronics using graphene-based film. The film can be attached to electronic components and has exhibited a conductive capacity four times greater than copper.

This is particularly important as electronic systems accumulate a great deal of heat which has a detrimental effect on performance, efficient energy usage and operational longevity. One study on heat control and dissipation concluded that half the energy required to run computer servers is used for cooling.

Professor Johan Liu at the Chalmers University of Technology first showed that graphene could have a cooling effect on silicon-based electronics. But as professor Liu pointed out, the amount of graphene that could be applied at that time did not have the ability to dissipate substantial amounts of heat because it consisted only of a few layers of thermal conductive atoms. Trying to add more layers of graphene ran into problems because the layers would not adhere to each other properly.

However, because a chemical bond that involves the sharing of electron pairs between atoms called a covalent bond can now be created between the graphene and the electronic component, those problems have been solved.

The stronger bonds result from the addition of a property-altering molecule, and the Chalmers researchers chose one that, when heated, created silane bonds between the graphene and the electronic component.

This silane coupling doubles the thermal conductivity of the graphene, and the researchers have shown that graphene-based film with 20 micrometre thickness can reach a thermal conductivity value four times that of copper.