Quantum dots enable plasmonic semis

April 19, 2011 // By R. Colin Johnson
Quantum dots enable plasmonic semis
Plasmonic semiconductors will revolutionize electronics by allowing the easy coupling of photons (light) and electrons, according to researchers at the U.S. Department of Energy (DOE) Lawrence Berkeley National Laboratory.

Plasmons are wavefronts that couple independent electrons together into quasi-particles that travel in waves on a surface, allowing their frequency to be matched to that of incident photons, thus coupling electronic plasmons with optical photons at resonance. Achieving such localized surface plasmon resonance in a semiconductor is predicted by Berkeley Lab enable electronic interconnects where signals are sped up to the speed of light, on-chip lenses for lasers and sensors, a new generation of super-efficient plasmonic light-emitting diodes (LEDs), a new generation of supersensitive chemical and biological detectors, as well as metamaterials that can bend light around object to create an invisibility cloak.

Until now plasmonic devices were based on interfaces between metals and insulators (dielectrics), but these new results claim that many common semiconductors can also be crafted to transport plasmons, according to Berkeley Lab, which reported achieving surface plasmon resonsances in vacancy-doped semiconductor nanocrystals—quantum dots.

"Doped semiconductor quantum dots open up the possibility of strongly coupling photonic and electronic properties, with implications for light harvesting, nonlinear optics, and quantum information processing," said Berkeley Lab Director Paul Alivisatos.

Surface plasmon resonances from p-type carriers in vacancy-doped copper-sulfide dots used quantum confinement to tune the electronic properties to the near-infrared range of the electromagnetic spectrum. The strong coupling between the photonic and electronic modes, the researchers claim, could be used to greatly enhance the exciton-light interactions of solar photovoltaics and artificial photosynthesis. Next, the team is experimenting with copper selenide and quermanium telluride semiconductors, to measure the expected enhancements in solar cells and memory devices made with them, respectively.

Funding was provided by the DOE's Office of Science.

Transmission electron micrograph (TEM) shows electron diffraction patterns (inset) of three quantum dot samples with average size of (a) 2.4 nanometers (b) 3.6 nm, and (c) 5.8 nm. Source: Lawrence Berkeley National Laboratory.

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