New Laser for Computer Chips

Schematic structure of the germanium-tin (GeSn) laser, applied directly onto the silicon wafer (blue) by using an intermediate layer of pure germanium (orange; source: FZ Jülich)

Schematic structure of the germanium-tin (GeSn) laser, applied directly onto the silicon wafer (blue) by using an intermediate layer of pure germanium (orange; source: FZ Jülich)

Scientists from Forschungszentrum Jülich and the Paul Scherrer Institute in cooperation with international partners have presented the first semiconductor consisting solely of elements of main group IV. As a consequence, the germanium-tin (GeSn) laser can be applied directly onto a silicon chip and thus creates a new basis for transmitting data on computer chips via light – faster than is possible with copper wires and with only a fraction of the energy.
The scientists at Jülich’s Peter Grünberg Institute PGI have now for the first time succeeded in creating a “real” direct main group IV semiconductor laser.  “The high tin content is decisive for the optical properties. For the first time, we were able to introduce more than 10% tin into the crystal lattice without it losing its optical quality,” reports PhD student Stephan Wirths. “The functioning of the laser is so far limited to low temperatures of up to minus 183 degrees Celsius, however. This is mainly due to the fact that we worked with a test system that was not further optimized,” adds group leader Dan Buca.
In cooperation with his colleagues from Prof. Siegfried Mantl’s group at PGI-9, Wirths applied the laser directly onto a silicon wafer whose properties were subsequently measured at the Paul Scherrer Institute in Switzerland. PhD student Richard Geiger fabricated the laser structures there. “That way, we were able to demonstrate that the germanium-tin compound can amplify optical signals, as well as generate laser light,” reports Hans Sigg from the Laboratory for Micro and Nanotechnology.
The laser was excited optically for the demonstration. Currently, the scientists in Buca’s group at Jülich are working on linking optics and electronics even more closely. The next big step forward will be generating laser light with electricity instead, and without the need for cooling if possible. The aim is to create an electrically pumped laser that functions at room temperature.
GeSn absorbs and emits light in a wavelength range of about 3 micrometres. Many carbon compounds, such as greenhouse gases or biomolecules, also display strong absorption lines at this boundary between near and mid-wavelength infrared. Hence, sensors made of GeSn promise a new possibility of detecting these compounds.
Along with computer chips, completely new applications that have not been pursued so far for financial reasons may thus benefit from the new laser material. Gas sensors or implantable chips for medical applications which can gather information about blood sugar levels or other parameters via spectroscopic analysis are examples. In the future, cost-effective, portable sensor technology – which may be integrated into a smart phone – could supply real-time data on the distribution of substances in the air or the ground and thus contribute to a better understanding of weather and climate development. (Source: FZ Jülich)

Reference: S. Wirths et al.: Lasing in direct bandgap GeSn alloy grown on Si, Nat. Photon., online 19 January 2015; DOI: 10.1038/nphoton.2014.321

Links:  Forschungszentrum Jülich

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