Advances in silicon photonics pave the way for cost-effective, high-performance optical devices

Imec, a research and innovation hub in the field of nanoelectronics and digital technologies, announced an important milestone in the field of silicon photonics with the successful demonstration of multiple quantum well nano-peak laser diodes at GaAs-based and electrically driven, entirely monolithicly fabricated on 300mm silicon wafers. in its CMOS pilot prototyping line.

By obtaining a room temperature continuous wave laser with threshold currents as low as 5 mA and output powers above 1 mW, the results, published in Naturedemonstrate the potential of direct epitaxial growth of high-quality III-V materials on silicon. This advancement paves the way for the development of cost-effective, high-performance optical devices for applications in data communications, machine learning and artificial intelligence.

The lack of highly scalable native light sources integrated into CMOS has been a major obstacle to the widespread adoption of silicon photonics. Hybrid or heterogeneous integration solutions, such as flip-chips, microtransfer printing, or chip-to-wafer bonding, involve complex bonding processes or the need for expensive III-V substrates that are often discarded after the treatment.

This not only increases costs but also raises concerns about sustainability and resource efficiency. For this reason, direct epitaxial growth of high-quality III-V optical gain materials, selectively on large silicon photonic wafers, remains a highly sought-after goal.

The significant mismatch in crystal lattice parameters and thermal expansion coefficients between III-V and Si materials inevitably initiates the formation of crystal mismatch defects, known to deteriorate laser performance and reliability. Selective area growth (SAG) combined with aspect ratio trapping (ART) significantly reduces defects in silicon-integrated III-V materials by confining unsuitable dislocations in narrow trenches etched into a dielectric mask.

“Over the past several years, Imec has pioneered nano-ridge engineering, a technique that leverages SAG and ART to develop low-defect III-V nano-ridges outside of the trenches. This approach not only further reduces defects, but also allows precise control of material dimensions and composition.

“Our optimized nano-ridge structures typically exhibit thread dislocation densities well below 10⁵ cm^-2. Today, imec leveraged the III-V nano-ridge engineering concept to demonstrate the first wafer-scale manufacturing of GaAs-based lasers electrically pumped onto standard 300mm silicon wafers, entirely within a CMOS pilot manufacturing line,” explains Bernardette Kunert, director scientist at imec.

Taking advantage of low-defect GaAs nano-ridge structures, the lasers integrate multiple InGaAs quantum wells (MQWs) as an optical gain region, integrated into an in situ doped pin diode and passivated with an InGaP capping layer. Achieving continuous wave operation at room temperature with electrical injection is a major breakthrough, overcoming challenges in power delivery and interface engineering.

The devices display a laser at ~10²⁰ nm with threshold currents as low as 5 mA, slope efficiencies up to 0.5 W/A, and optical powers up to 1.75 mW, presenting a scalable path for high-performance silicon integrated light sources.

“Cost-effective integration of high-quality III-V gain materials on large diameter Si wafers is a key enabler for next-generation silicon photonics applications. These exciting nanoridge laser results represent an important step in the use of direct epitaxial growth for monolithic III-V integration.

“This project is part of a larger guiding mission led by IMEC to advance III-V integration processes towards higher technology readiness, from hybrid flip-chip and printing techniques through short-term transfer, to heterogeneous wafer and chip bonding technologies and, ultimately, long-term direct epitaxial growth,” says Joris Van Campenhout, silicon photonics researcher and R&D program director affiliated with the industry on optical I/O at imec.