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Quantum dot lasers have commercial future

17 Jun 2002

Quantum dot lasers could be on the market in five years' time, says Kenichi Nishi of NEC's Opto-Electronics Basic Research Laboratory, in Japan.

He told the Gordon Conference on 'Thin Film and Crystal Growth Mechanisms', held at Plymouth State College, US, in June that he and co-workers are already incorporating the uniform, high-aspect-ratio quantum dots into laser diodes.

Quantum dots are formed when one semiconductor material, such as indium arsenide, is deposited on a layer of another, like gallium arsenide. Instead of mixing, the indium arsenide collects on the surface as nanoscale sized islands. There can be more than 100 of these islands in a region just one micrometre square and each may be less than about 30 nanometres across and 20 nanometres high. The small size of these dots gives them valuable optical and electrical properties.

The attraction of quantum dot lasers includes tiny drive voltages, new emission wavelengths and operation at high temperatures. Nishi believes that these lasers should work up to temperatures of about 100 degrees Celsius.

One of the main challenges in making the lasers is precise fabrication of the dots. Nishi's team grows quantum dots by a technique known as molecular beam epitaxy. This allows them to deposit layers very accurately. The team has also used electron diffraction patterns to characterize the dots as they form.

Nishi's predictions for commercial quantum dot lasers in five years' time rely on a large research effort but he is confident about the benefits of the technology. "Quantum dots will improve not only the laser performance but also other device characteristics like optical amplifiers, detectors and switches."

  • At the same meeting, Jerry Floro and colleagues at Sandia National Laboratories, Brown University and the University of Illinois at Urbana-Champaign in the US discussed the first experiments which show that quantum dots mutually repel each other. This result helps to understand how the dots form and might be controlled. The size of the dots is important because smaller dots give shorter emission wavelengths. Uniform sizes give uniform frequencies.

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