Nanocrystal quantum-dot lasers show promise

17 Jun 2002

Scientists at the US Department of Energy's Los Alamos National Laboratory and Massachusetts Institute of Technology have demonstrated that nanoscale semiconductor particles, called nanocrystal quantum dots, offer the necessary performance for the efficient emission of laser light. The research appears in 13 October issue of Science.

The demonstrated performance of the nanocrystals opens the door for developing novel optical and optoelectronic devices, such as tunable lasers, optical amplifiers and light-emitting diodes, from assemblies of these particles.

"Our results provide a proof-of-principle and should motivate the development of nanocrystal quantum-dot-based lasers and amplifiers," said Victor Klimov of Los Alamos, who led the research effort.

Quantum dots are so small that quantum-mechanical effects come into play in controlling their behavior.

In quantum dots, the electrons are confined in a small volume that forces them to interact strongly with each other. These interactions can lead to the deactivation of the dot through the so-called "Auger process", preventing the dot from emitting a photon.

The Los Alamos-led researchers examined quantum dots formed from several different types of crystalline material. They showed that the quantum dots exhibit a sufficiently large optical gain for stimulated emission to overcome the nonradiative Auger process. Stimulated emission, or lasing, was only possible, however, when the dots were densely packed in the sample.

Quantum dots offer this performance over a range of temperatures, which makes them suitable for a variety of applications. They can also be tuned to emit at different wavelengths, or colors. The emission wavelength of a quantum dot is a function of its size, so, by making dots of different sizes, scientists can create light of different colors.

The quantum-dot material that Klimov and his colleagues worked with is easily manipulated through well-established chemical-synthesis methods. Fabricating densely packed quantum-dot arrays should be a straightforward material-processing challenge.