The Last Missing Piece Of The Silicon Photonics Puzzle

International research team develops first electrically pumped, continuous laser for seamless integration into silicon chips

An international research team has reached a milestone in silicon photonics: They have developed the first electrically pumped semiconductor laser for continuous operation that consists entirely of elements from the fourth main group - the "silicon group". The new laser is based on ultra-thin layers of silicon-germanium-tin and germanium-tin and can be integrated directly into silicon chips. This solves a central problem of on-chip photonics: the seamless connection of optical and electronic components on a single chip. The results of the research work were published in the journal Nature Communications .

With the rapid advances in artificial intelligence (AI) and the Internet of Things (IoT), i.e. the increasing networking of intelligent devices, the need for powerful and energy-efficient hardware is increasing. Optical data transmission offers clear advantages here: It enables the transport of large amounts of data with minimal interference and energy losses. While it is currently used primarily for distances of more than one meter, optical data transmission is increasingly proving to be advantageous over shorter ranges as well. A key goal is the integration of corresponding optical components directly into microprocessors - these would then be formed directly during chip production, similar to transistors. The focus of research is therefore on the development of cost-effective photonic integrated circuits (PICs), which can both improve performance and reduce manufacturing costs.

Silicon photonics has made great progress in recent years. Key components such as high-performance modulators, photodetectors and waveguides have already been successfully integrated monolithically on silicon chips. However, one key component was missing until now: an electrically pumped light source based exclusively on materials from the fourth main group. Commonly used III-V semiconductors from other main groups are difficult to combine with silicon - a material on which the entire chip production is based. This makes production complex and expensive. The new laser closes this gap and is therefore considered the "last missing piece of the puzzle" in silicon photonics. Since it is compatible with classic CMOS technology, it can be seamlessly integrated into existing silicon processes.

The laser is based on a so-called multi-quantum well structure, which consists of ultra-thin layers of silicon-germanium-tin and germanium-tin. The structure was specially adapted to the properties of these alloys. Complemented by a new ring geometry, it minimizes energy consumption and heat generation and thus enables stable continuous operation at 90 Kelvin.

In contrast to earlier germanium-tin lasers, which were optically pumped and required high energies, the new laser also works electrically. It requires just a current of 5 milliamperes and a voltage of 2 volts - comparable to a light-emitting diode. Manufactured on standard silicon wafers, this laser is the first "really usable" laser made from semiconductors of the fourth main group.

Although the laser already represents a significant advance, there is still room for improvement. In particular, the laser threshold must be further reduced and stable operation at room temperature must be enabled. Earlier germanium-tin lasers, which were initially only optically pumped and were suitable for use at cryogenic temperatures, show the development potential: they have now been successfully adapted for operation at room temperature.

An optically pumped laser is excited by an external light source to produce the laser light. In an electrically pumped laser, this is done by an electric current. Electrically pumped lasers are generally more energy efficient because they convert electricity directly into laser light.

The research group led by Dr. Dan Buca at PGI-9 of the Jülich Research Center has been doing pioneering work in the field of tin-based group IV alloys for years. In close collaboration with partners such as the IHP, the University of Stuttgart, CEA-Leti, C2N-Université Paris-Sud and the Politecnico di Milano, the researchers have already demonstrated the potential of these material systems for applications in photonics , electronics , thermoelectrics and spintronics . With the development of the new laser, the vision of fully integrated silicon photonics as an all-in-one solution for the next generation of microchips is within reach.