Ultrafast photodetectors made of carbon nanotubes

Create: 03/07/2011 - 00:00
Carbon nanotubes are promising elements for opto-electronic components. So far, however, lacked electronic methods to analyze time-resolved optical and electronic properties of nanotubes. A team of physicists led by Professor Alexander Holleitner from the Technical University of Munich (TUM) has now developed a method by which they can measure just how fast electrons move in these extremely small photodetectors.

Carbon nanotubes have a variety of exceptional properties. They are promising candidates for opto-electronic components. But so far, it is extremely difficult to analyze their optical and electronic properties and influence. Now, scientists led by Professor Alexander Holleitner, a physicist at the Technical University of Munich and member of the cluster of excellence Nanosystems Initiative Munich (NIM) to develop a measurement method that allows a time resolution of the so-called photocurrent in photo-detectors into the picosecond range.

"A picosecond is a very small interval of time," said Alexander Holleitner. "Had the speed of light, the electrons move, they would in a second, almost to the moon. In contrast, a picosecond they came only about a third of a millimeter wide. "The new metering technology is around one hundred times faster than existing methods. According to the researchers led by Professor Alexander Holleitner can now measure the speed of the electrons exactly. In carbon nanotubes, the electrons back into place a picosecond only about 8 ten-thousandths of a millimeter, or 800 nanometers.

Core of the photodetector are investigated carbon nanotubes with a diameter of only about one nanometer, which are integrated electronically via metallic contacts. The speed of the electrons determine the physicists using coplanar strip lines, they evaluate about a particular time-resolved laser spectroscopy method, the pump-probe technique. Here are excited with a laser pulse the electrons in carbon nanotubes and monitor the dynamics of this process with two lasers.

The newly developed method provides many new insights and analysis capabilities that are of interest for a number of applications. This primarily involves the development of optoelectronic components such as nanoscale photodetectors, photo switches and solar cells.

The work was supported by the Deutsche Forschungsgemeinschaft (excellence cluster Nanosystems Initiative Munich, NIM) and the Center for NanoScience (CeNS) at the Ludwig-Maximilians University in Munich. At the publication also worked with physicists at the University of Regensburg and the Swiss Federal Institute of Technology in Zurich.

Picosecond Time-Resolved Photo Currents in Carbon Nanotubes Contacted, Leonhard Prechtel, Li Song, Stephan Manus, Dieter Schuh, Werner Wegscheider, Alexander W. Holleitner, Nano Letters 2011, 11 (1), pp 269-272, DOI: 10.1021/nl1036897

Source: Technical University Munich

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