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Breakthrough in Semiconductor Lasers: Advancing Silicon Photonics

A collaborative team of scientists from Forschungszentrum Jülich (FZJ), the University of Stuttgart, and the Leibniz Institute for High Performance Microelectronics (IHP), along with their French partner CEA-Leti, has successfully developed the inaugural electrically pumped continuous-wave semiconductor laser constructed entirely from elements in the fourth group of the periodic table. This pioneering laser, which incorporates stacked ultrathin layers of silicon germanium-tin and germanium-tin, represents a significant advancement as it is the first to be directly grown on a silicon wafer. This innovation paves the way for enhanced on-chip integrated photonics, as detailed in the journal Nature Communications.

The surge in artificial intelligence (AI) technologies and the Internet of Things (IoT) is escalating the demand for hardware that is not only more powerful but also energy-efficient. Optical data transmission has emerged as a crucial method for moving large quantities of data while minimizing energy losses, proving advantageous even for relatively short distances. This trend suggests an imminent shift towards microchips that feature low-cost photonic integrated circuits (PICs), promising considerable cost reductions and performance enhancements.

Recent advancements have led to the successful monolithic integration of optically active components on silicon chips. Significant components such as high-performance modulators, photodetectors, and waveguides have been established. However, the sector has faced challenges due to the absence of a viable, electrically pumped light source limited to Group IV semiconductors, as traditional light sources tended to use III-V materials. These materials are often complex and expensive to integrate with silicon. The newly developed laser fills this critical gap, aligning with existing CMOS technologies for chip fabrication and facilitating seamless integration into current silicon manufacturing workflows, thereby acting as a vital addition to silicon photonics capabilities.

For the first time, this research demonstrates continuous-wave operation in an electrically pumped Group IV laser on silicon. In contrast to earlier germanium-tin lasers, which required high-energy optical pumping, this latest version functions with a low current injection of just 5 milliamperes (mA) at 2 volts (V), similar to the energy requirements of light-emitting diodes. Its innovative multi-quantum well structure and ring geometry enable minimized power consumption and reduced heat generation, allowing stable operation at temperatures up to 90 Kelvin (K), or minus 183.15 degrees Celsius (°C).

This laser is produced on standard silicon wafers similar to those utilized for silicon transistors, marking it as the first truly “usable” Group IV laser. Nevertheless, further refinements are necessary to lower the lasing threshold and achieve room-temperature operation. However, the advancement from earlier optically pumped germanium-tin lasers from cryogenic environments to room temperature within a few years indicates a promising trajectory for future developments.

The main distinction between optical and electrical pumping lies in their operation: optically pumped lasers require an external light source to generate the lasing light, while electrically pumped lasers produce light through the injection of electrical current into the diode. This makes electrically pumped lasers generally more energy-efficient, as they directly convert electricity into laser light.

The research, spearheaded by Dr. Buca from Forschungszentrum Jülich’s PGI-9, has made significant strides in exploring tin-based Group IV alloys over the years, collaborating with institutions such as IHP, the University of Stuttgart, CEA-Leti, C2N-Université Paris-Sud, and Politecnico di Milano. This work lays the groundwork for potential applications across various sectors, including photonics, electronics, thermoelectrics, and spintronics. With this breakthrough, the comprehensive vision of silicon photonics emerges closer to realization, offering an integrated solution for next-generation microchips.

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