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Quantum dots enable photon-electron coupling

Posted: 26 Apr 2011 ?? ?Print Version ?Bookmark and Share

Keywords:plasmonic semiconductors? quantum dots? surface plasmon resonance? photon-electron coupling?

A research team from the U.S. Department of Energy (DOE) Lawrence Berkeley National Laboratory expects plasmonic semiconductors to transform electronics with its ability to facilitate coupling of photons (light) and electrons.

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. Berkeley Lab predicts that achieving such localized surface plasmon resonance in a semiconductor would 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 LEDs, a new generation of supersensitive chemical and biological detectors, as well as metamaterials that can bend light around objects 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 resonances in vacancy-doped semiconductor nanocrystalsquantum 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.

electron diffraction patterns

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

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.

- R. Colin Johnson
??EE Times

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