California group achieves integration of quantum dot lasers on silicon chiplets...

21 Jul 2025

...while German researchers develop stable alloy of carbon, silicon, germanium, and tin.

Lasers that are fabricated directly onto silicon photonic chips offer several advantages over external laser sources, such as greater scalability. Furthermore, photonic chips with these “monolithically” integrated lasers can be commercially viable if they can be manufactured in standard semiconductor foundries.

III-V semiconductor lasers can be monolithically integrated with photonic chips by directly growing a crystalline layer of laser material, such as indium arsenide, on silicon substrate. However, photonic chips with such integrated laser source are challenging to manufacture due to mismatch between structures or properties of III-V semiconductor material and silicon.

So-called “coupling loss” or the loss of optical power during transfer from laser source to silicon waveguides in the photonic chip is yet another concern when manufacturing photonic chips with monolithically integrated lasers.

In a study that was recently published in the IEEE Journal of Lightwave Technology, Dr. Rosalyn Koscica from the University of California Santa Barbara, and her team successfully integrated indium arsenide quantum dot (QD) lasers monolithically on silicon photonics chiplets. Dr. Koscica said, “Photonic integrated circuit applications call for on-chip light sources with a small device footprint to permit denser component integration.”

To achieve this monolithic integration, the authors combined three key concepts: the pocket laser strategy for monolithic integration, a two-step material growth scheme that includes both metalorganic chemical vapor deposition and MBE for a smaller initial gap size, and a polymer gap-fill approach to minimize optical beam divergence in the gap, to develop monolithically integrated QD lasers on silicon photonics chiplets.

On testing, the chiplets with monolithically integrated lasers demonstrated sufficiently low coupling loss. As a result, the QD lasers operate efficiently on a single O-band wavelength within chiplets. The O-band wavelength is desirable as it allows for transmission of signals within photonic devices with low dispersion. Lasing in the single frequency is achieved using ring resonators made from silicon or distributed Bragg reflectors made from silicon nitride.

“Our integrated QD lasers demonstrated a high temperature lasing up to 105 °C and a life span of 6.2 years while operating at a temperature of 35 °C,” said Dr. Koscica. The laser integration technique has the potential to be adopted widely due to two reasons. Firstly, the photonics chips can be manufactured in standard semiconductor foundries. Secondly, the QD laser integration technique can work for a range of photonic integrated chip design without needing extensive or complex modifications.

Researchers develop alloy of carbon, silicon, germanium, and tin

Researchers at German research centers Forschungszentrum Jülich and the Leibniz Institute for Innovative Microelectronics (IHP), located in Frankfurt on Oder, have developed a material that has never existed before: a stable alloy of carbon, silicon, germanium, and tin.

The achievement is described in Advanced Materials. The new compound, abbreviated as CSiGeSn, opens up exciting possibilities for applications at the interface of electronics, photonics, and quantum technology. What makes this material special is that all four elements, like silicon, belong to Group IV of the periodic table. This ensures compatibility with the standard manufacturing method used in the chip industry — the CMOS process — a crucial advantage.

“By combining these four elements, we have achieved a long-standing goal: the ultimate Group IV semiconductor,” said Dr. Dan Buca from Forschungszentrum Jülich. The new alloy makes it possible to fine-tune material properties to a degree that enables components beyond the capabilities of pure silicon — for instance, optical components or quantum circuits. These structures can be integrated directly onto the chip during manufacturing.

Buca’s team together with various research groups had already succeeded in combining silicon, germanium, and tin to develop transistors, photodetectors, lasers, LEDs, and thermoelectric materials. The addition of carbon now provides even greater control over the band gap — the key factor that determines electronic and photonic behaviour. “An example is a laser that also works at room temperature. Many optical applications from the silicon group are still in their infancy,” said Buca. “There are also new opportunities for the development of suitable thermoelectrics to convert heat into electrical energy in wearables and computer chips.”

For a long time, manufacturing such a material was thought to be virtually impossible. Carbon atoms are tiny while the tin atoms are large, and their bonding forces very different. Only through precise adjustments to the production process was it possible to combine these opposites — using an industrial CVD system from deposition systems supplier Aixtron. No special apparatus was required, just equipment similar to that already standard in chip manufacturing.

“The material offers a unique combination of tunable optical properties and silicon compatibility,” said Prof. Dr. Giovanni Capellini from IHP, who has been working with Dan Buca for more than ten years to explore the application potential of new Group IV semiconductors. “This lays the foundation for scalable photonic, thermoelectric and quantum technology components,” said Prof. Capellini.