Researchers develop “last missing piece” of silicon photonics
Scientists have reported the first electrically pumped continuous-wave semiconductor laser suitable for seamless silicon integration, bringing the vision of silicon photonics providing an “all-in-one” solution for next-generation microchips within reach
Scientists from Forschungszentrum Jülich (FZJ), the University of Stuttgart, and the Leibniz Institute for High Performance Microelectronics (IHP), together with their French partner CEA-Leti, have reported the first electrically pumped continuous-wave semiconductor laser composed exclusively of elements from the fourth group of the periodic table – the “silicon group”. Built from stacked ultrathin layers of silicon germanium-tin and germanium-tin, this new laser is the first of its kind directly grown on a silicon wafer, the team says, opening up new possibilities for on-chip integrated photonics. The findings have been published in Nature Communications.
The rapid growth of AI and the Internet of Things (IoT) are driving the demand for increasingly powerful, energy-efficient hardware. Optical data transmission, with its ability to transfer vast amounts of data while minimising energy loss, is already the preferred method for distances above one metre and is proving advantageous even for shorter distances. This development points towards future microchips featuring low-cost PICs, offering significant cost savings and improved performance.
In recent years, significant progress has been made in monolithically integrating optically active components on silicon chips. Key components, including high-performance modulators, photodetectors, and waveguides have been developed. However, a long-standing challenge has been the lack of an efficient, electrically pumped light source using only Group IV semiconductors. Until now, such light sources have traditionally relied on III-V materials, which are difficult and expensive to integrate with silicon. The researchers say their new laser addresses that gap, making it compatible with the conventional CMOS technology for chip fabrication and suitable for seamless integration into existing silicon manufacturing processes. It could therefore be seen as the “last missing piece” in the silicon photonics toolbox.
“We have been exploring the fascinating possibilities of germanium-tin alloys for almost a decade,” said Dan Buca from Forschungszentrum Jülich’s PGI-9, who led the research group. “The development of an efficient, electrically pumped laser has been one of our major goals from the very beginning. This breakthrough is further proof of the enormous potential of the germanium-tin alloys for different applications, in this specific case for photonic applications.”
According to the scientists, they have for the first time demonstrated continuous-wave operation in an electrically pumped Group IV laser on silicon. Unlike previous germanium-tin lasers that relied on high-energy optical pumping, this new laser is reported to operate with a low current injection of just 5 mA at 2 V, comparable to the energy consumption of a light-emitting diode. With its advanced multi-quantum well structure and ring geometry, the laser minimises the power consumption and the heat generation, enabling stable operation up to 90 K or -183.15 degrees C, the researchers add.
Grown on standard silicon wafers like those used for silicon transistors, this development could be the first truly “useable” Group IV laser, though further optimisations are needed to further reduce the lasing threshold and achieve room-temperature operation. However, the success of earlier optically pumped germanium-tin lasers, which have evolved from cryogenic to room-temperature operation in only few years, suggests a potential path forwards.
In an optically pumped laser, an external light source is required to generate the lasing light, whereas an electrically pumped laser generates light when an electrical current is passing through the diode. Electrically pumped lasers are usually more energy-efficient as they directly convert electricity directly into laser light.
With this new achievement, the researchers say the vision of silicon photonics providing an all-in-one solution for next-generation microchips is now within reach.
Image credit: Forschungszentrum Jülich / Jhonny Tiscareno
