New properties discovered in diamond semiconductors

Diamond, often celebrated for its unrivaled hardness and transparency, has become an exceptional material for high-power electronics and next-generation quantum optics. Diamond can be made to be as electrically conductive as a metal, by introducing impurities such as the element boron.

Researchers at Case Western Reserve University and the University of Illinois at Urbana-Champaign have discovered another interesting property of boron-added diamonds, known as boron-doped diamonds.

Their findings could pave the way for new types of biomedical and quantum optical devices that are faster, more efficient, and capable of processing information in ways that classical technologies cannot. Their results are published in Natural communication.

Researchers have discovered that boron-doped diamonds exhibit plasmons – waves of electrons that move when light hits them – allowing electric fields to be controlled and enhanced at the nanoscale. This is important for advanced biosensors, nanoscale optical devices and for the improvement of solar cells and quantum devices.

Previously, boron-doped diamonds were known to conduct electricity and become superconductors, but did not have plasmonic properties. Unlike metals or even other doped semiconductors, boron-doped diamonds remain optically clear.

“The diamond continues to shine,” said Giuseppe Strangi, professor of physics at Case Western Reserve, “both literally and as a beacon of scientific and technological innovation. As we move forward into the era of quantum computing and communication, discoveries like this bring us closer to harnessing the full potential of materials at their most fundamental level.”

“Understanding how doping affects the optical response of semiconductors like diamond changes our understanding of these materials,” said Mohan Sankaran, professor of nuclear, plasma and radiological engineering at the Illinois Grainger College of Engineering.

Plasmonic materials, which affect light on the nanoscale, have captivated humans for centuries, even before their scientific principles were understood. The vibrant colors of medieval stained glass windows result from metallic nanoparticles embedded in the glass.

When light passes through them, these particles generate plasmons that produce specific colors. Gold nanoparticles appear ruby ​​red, while silver nanoparticles display a bright yellow. This ancient art highlights the interaction between light and matter, inspiring modern advances in nanotechnology and optics.

Diamonds, composed of transparent crystals of the element carbon, can be synthesized with small amounts of boron, adjacent to carbon in the periodic table. Boron contains one less electron than carbon, allowing it to accept electrons. Boron essentially opens a periodic electronic “hole” in the material, which has the effect of increasing the material’s ability to conduct current. The boron-doped diamond network remains transparent, with a blue tint. (The famous Hope Diamond is blue because it contains small amounts of boron).

Due to its other unique properties (it is also chemically inert and biologically compatible), boron-doped diamond could potentially be used in contexts that other materials could not, such as for medical imaging or biochips or sensors high sensitivity molecules.

Low-pressure synthesized diamonds were developed at Case Western Reserve (then Case Institute of Technology) in 1968 by faculty member John Angus, who died in 2023. Angus was also the first to report on electrical conductivity boron-doped diamond.