The findings show that excitons, quasiparticles that transport energy, last long enough for a broad range of potential applications, including bits in quantum computing devices.
Dr. Anton Malko, professor of physics in the School of Natural Sciences and Mathematics, is the author of a paper published online on March 30 in Advanced Materials that describes tests on ultrathin semiconductors made with a recently developed laser-assisted method synthesis technique (LAST). The findings show novel quantum physics at work.
Semiconductors are a class of crystalline solids whose electrical conductivity is between a conductor and an insulator. This conductivity can be externally controlled by doping or electrical gating, making them vital elements for the diodes and transistors that underpin all modern electronic technology.
Two-dimensional transition metal dichalcogenides (TMDs) are a novel type of ultrathin semiconductor consisting of a transition metal and a chalcogen element arranged in one atomic layer. While TMDs have been explored for a decade, the 2D form that Malko examined has advantages in scalability and optoelectronic properties.
“LAST is a very pure method. You take pure molybdenum or tungsten, and pure selenium or sulfur, and evaporate them under intense laser light,” Malko said. “Those atoms are distributed onto a substrate and make the two-dimensional TMD layer less than 1 nanometer thick.”
A material’s optical properties are partially determined by the behavior of excitons, quasiparticles that can transport energy while remaining electrically neutral.
“When a semiconductor absorbs a photon, it creates in the semiconductor a negatively charged electron paired with a positive hole, to maintain neutral charge. This pair is the exciton. The two parts are not completely free from each other—they still have a Coulomb interaction between them,” Malko said.