Silicon, the second most abundant material on Earth, could be used by scientists to develop low-cost lasers.

Researchers at the Belgian research center Imec have achieved a significant innovation in the integration of lasers with silicon, utilizing gallium arsenide, a material that typically does not bond with silicon. This advancement has the potential to reduce costs and improve the quality of photonic chips, especially in applications related to artificial intelligence and telecommunications.

Silicon photonics relies on the use of light to transmit data, thereby overcoming the limitations of electrical signals. However, while silicon is a material commonly found in sand, it does not have the capacity to generate light efficiently, meaning that lasers are required as light sources. Historically, integrating lasers into chips has been complicated because silicon is not suitable for their fabrication, and the most effective materials for lasers, such as gallium arsenide, do not naturally integrate with it. Existing methods involve bonding these two materials, a process that is costly and inefficient.

To address this challenge, Imec scientists have developed a technique that allows lasers to be grown directly on silicon. This discovery could facilitate the creation of more affordable and scalable photonic devices, significantly transforming applications in data communication, machine learning, and artificial intelligence.

The methodology adopted by Imec, described in a publication in the journal Nature, is based on the engineering of nano-crest structures, which confine defects that could affect laser performance. The process begins by covering a silicon wafer with a layer of silicon dioxide and etching arrow-shaped trenches. Gallium arsenide is then deposited in these trenches, where it only touches the silicon at the bottom. This arrangement allows defects to remain at the bottom of the trench, preventing them from propagating into the laser material.

The lasers use indium-gallium-arsenide (InGaAs) quantum wells as the optical gain region and are integrated into a p-i-n doped diode structure. They operate at room temperature via continuous electrical injection, achieving threshold currents as low as 5 mA and output powers of up to 1.75 mW.

Bernardette Kunert, Imec's scientific director, emphasized that in recent years, the center has pioneered the engineering of nano-crest structures, a technique that enables the growth of III-V nano-crest structures with low defectivity outside of the trenches. This approach has facilitated the scalable manufacturing of GaAs-based lasers on standard 300 mm silicon wafers, entirely within a CMOS pilot manufacturing line.

The nano-crest lasers emit light at 1,020 nanometers, a shorter wavelength than typically used in telecommunications. Imec researchers are actively working to extend the wavelength and refine the design, aiming to reduce defects near the electrical contacts. If these efforts succeed, this technique could provide a scalable and cost-effective solution for integrating lasers into silicon photonics, potentially paving the way for high-performance optical devices in the future.