Existing methods of optical signal transmission offer a high bandwidth, but are not suited for data transfer across very short distances such as on-chip interconnects between processor and memory or between various processor cores in a large multiprocessor array. This is because the materials used to implement solid-state laser diodes (so-called III-V semiconductors) are belonging to different chemical groups than silicon. This results in different lattice structures which prevents cost-effective integration of such components.
Silicon and germanium, in contrast, are belonging to the same group in the periodic table of elements, the so-called indirect semiconductors. Due to the energetic states of their electrons they are not capable of emitting or absorbing photons and thus light. The addition of tin however modifies the electronic properties of the crystal. The resulting compound is a direct semiconductor that can emit and absorb photons directly – that is to say at high efficiency.
Since tin, like silicon and germanium both belong to the fourth main group of the periodic system, the silicon-germanium-tin diode (or short: SiGeSn diode) can be produced on a silicon wafer much like the known semiconductor manufacturing processes. The scientists who discovered this feature manufactured the diode in a layered GeSn/SiGeSn system. This sandwich approach increases the efficiency at which the injected electric current is transformed into light. By gradually modifying the silicon and tin content, the team also succeeded in varying the optical wavelength of the light with a range between 2 to 2.6 micrometers.
By developing this diode, the researchers from the Peter Grünberg Institute of the Jülich Research Center have made a great step towards creating an infrared light source for on-chip data communications. Beyond, the material could enable further applications such as photo detectors.
Already back in January 2015, the same team of physicists demonstrated the basic suitability of SiGeSn compound materials for such purposes by means of a laser component that could be integrated to a silicon substrate. In contrast to the earlier development, the recent diode works at ambient temperature.
The research work has been published originally in the Optica and Nature Photonics magazines.
Further information (video): https://youtu.be/SIgPNEwmsKs (in German)