Ultrafast Photodetectors Made from Carbon Nanotubes

A measurement technique claiming to be 100 times faster than any existing method can measure the dynamics of photoexcited electrons in nanoscale photodetectors using a time-resolved laser spectroscopy process. The new technique allowed Alexander Holleitner and scientists at the Technical University of Munich to measure the precise speed of electrons, which in carbon nanotubes travel about 800 nm in one picosecond.

With this measurement setup, scientists can resolve the ultrafast optoelectronic dynamics of carbon nanotubes. A first laser excites electrons in the carbon nanotubes spanning the gap between two gold electrodes while a second laser measures the resulting photocurrent. (Image: Dr. A. Holleitner, TUM)

At the heart of the photodetectors are carbon nanotubes spanning a tiny gap between two gold detectors. The scientists measured the speed of the electrons by means of a pump-probe technique in which a laser pulse is used to excite electrons in the carbon nanotubes and a second laser is used to observe the dynamics of the process.

The insights and analytic opportunities made possible by the technique are relevant to an entire range of applications, including the development of optoelectronic components such as nanoscale photodetectors, photoswitches and solar cells, said the scientists.

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