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GaAs nanomembrane cooling by laser interaction

Posted: 25 Jan 2012 ?? ?Print Version ?Bookmark and Share

Keywords:semiconductor membrane? GaAs? nanomembrane cooling?

A team of researchers at the Niels Bohr Institute, University of Copenhagen, has discovered a new method for cooling semiconductor membranes. They were able to experimentally cool membrane fluctuations to -269C by laser heating the membrane.

In the experiment, a 160nm gallium arsenide (GaAs) semiconductor membrane with surface area of 1 x 1mm was made to interact with the laser light in such a way that its mechanical movements affected the light that hit it. "We carefully examined the physics and discovered that a certain oscillation mode of the membrane cooled from room temperature down to -269C, which was a result of the complex and fascinating interplay between the movement of the membrane, the properties of the semiconductor and the optical resonances," described Koji Usami, associate professor at Quantop at the Niels Bohr Institute.

laser light

The experiments are carried out in the Quantop laboratories at the Niels Bohr Institute. The laser light that hits the semiconducting nanomembrane is controlled with a forest of mirrors. (Photo: Ola J. Joensen)

The experiment consisted of shining the laser light onto the nanomembrane in a vacuum chamber. When the laser light hits the semiconductor membrane, some of the light is reflected and the light is reflected back again via a mirror in the experiment so that the light flies back and forth in this space and forms an optical resonator. Some of the light is absorbed by the membrane and releases free electrons. The electrons decay and thereby heat the membrane and this gives a thermal expansion. In this way the distance between the membrane and the mirror is constantly changed in the form of a fluctuation, noted Usami.

semiconductor nanomembrane

The nanomembrane has a surface area of 1 x 1mm and a thickness of 160nm. (Photo: Ola J. Joensen)

"The paradox is that even though the membrane as a whole is getting a little bit warmer, the membrane is cooled at a certain oscillation and the cooling can be controlled with laser light," added Usami.

Researchers believe that efficient cooling of mechanical fluctuations of semiconducting nanomembranes by means of light could lead to the development of new sensors for electric current and mechanical forces, and could replace expensive cryogenic cooling used today.

- Nicolas Mokhoff
??EE Times

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