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Micropyramid emits antibunched photons in the ultraviolet

In short: Linearly polarized photons emitted one by one form the basis for novel cryptography methods. Here we demonstrate that the photons emitted from InGaN quantum dots formed on the apex of a micropyramid exhibit single photon characteristics known as antibunching. Our experiments show that the InGaN quantum dot itself is a fast and close to perfect single photon emitter, but a background signal from the pyramid has to be eliminated before utilization in polarization-based single photon applications.

Linearly polarized photons emitted one by one form the basis for novel unbreakable cryptography methods. Therefore, there is a search for site controlled single photon emitters emitting linearly polarized light. One promising candidate is small inclusions of InGaN inserted at the apex of micron sized hexagonal GaN pyramids.  These inclusions are ruled by quantum mechanical effects and referred to as quantum dots. Such quantum dots have properties in common with single atoms - they are single photon emitters in a well-defined and narrow spectral range. The single photon properties have previously never been tested for the InGaN pyramidal system.

The statistics of the photon emission is measured with Time Correlated Single Photon Spectroscopy (TCSPS). In TCSPS, the time differences between subsequent photons are recorded on a picosecond time scale and placed in corresponding bins of a histogram. For a perfect quantum dot measured under ideal conditions, this correlation histogram has a vanishing value for zero time difference – indicating that two photons are never emitted simultaneously.

A TCSPS system was recently set up in our lab for investigating the photon statistics of the InGaN/GaN pyramidal structures emitting in the ultraviolet spectral range. A significant dip could be observed in the autocorrelation histogram and we could for the first time rigorously prove that the light of about 400 nm wavelengths originates from of a QD formed at the pyramid apex. However, the dip does not vanish at zero time difference. We demonstrate, by modelling, that the diminishing of the dip mainly is due to two effects: 1) the pyramid emits a background of uncorrelated photons in addition to the quantum dot emission and 2) the typical time between photons emitted from the QD (only 320 picoseconds) is shorter than the stochastic time spread of the instrument.
These results are very promising since they demonstrate that the InGaN quantum dot itself is a fast and close to perfect single photon emitter suitable for polarization-based applications, such as cryptography, if the background emission can be reduced.

Details of the research are described in Applied Physics Letters 105, 081901 (2014)


Fredrik Karlsson, associate professor
Phone: +46 (0)13 28 25 33
E-mail: freka@ifm.liu.se


  • Carl Trygger Foundation for Scientific Research
  • Swedish Research Council (VR)
  • Swedish Foundation for Strategic Research (SSF)
  • Knut and Alice Wallenberg Foundation
  • Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linköping University
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Responsible for this page: Fredrik Karlsson
Last updated: 12/02/14