Quantum dots – semiconductor structures in which electrons are confined in all three dimensions – have been intensively studied over the last two decades for both fundamental and technological reasons. The structures could be ideal for making a new generation of semiconductor lasers with lower threshold currents and higher efficiencies, as well as light-emitting diodes, solar cells and other photonic devices.

More recently, researchers have turned their attention to hybrid structures containing both semiconductor quantum dots and periodic arrays of metallic nanoparticles. These nanostructured plasmonic systems show improved optical characteristics and might come in useful for a variety of photonic applications, such as photocatalysis, light harvesting and all-optical switching. The improved properties come thanks to the interactions between the excitons in the semiconductor and the collective oscillations of electrons on the metal surface. These oscillations are known as plasmons – quasiparticles that carry light energy.

Improved optical response

In their work, Andrey Rogach and colleagues studied the optical properties of hybrid structures composed of cadmium telluride quantum dots and gold nanoparticle arrays. The researchers found that they could dramatically increase the light emitted by the structures by tuning the gold surface plasmon resonance to the exciton transitions in the semiconductor quantum dots. "This is possible because the two materials are confined in the same small space – something that leads to the local electromagnetic field of the metal surface plasmon being enhanced," explained team member Ming Fu. "The interaction of the enhanced field and the excitons in the semiconductor dots can then improve the optical response of the entire system."

To date, the researchers have only studied the luminescence of the hybrid semiconductor-metal structures. They now plan to investigate the fluorescence behaviour of the materials using techniques like confocal microscopy. "These experiments will hopefully help us glean more information about the interactions between metal particles and semiconductor quantum dots in general," said Fu.

The work was published in Applied Physics Letters.