Research hub imec has demonstrated the monolithic fabrication of electrically-driven gallium arsenide (GaAs)-based multi-quantum-well nano-ridge laser diodes on 300mm silicon wafers in its CMOS pilot prototyping line. Achieving room-temperature continuous-wave lasing with threshold currents as low as 5 mA and output powers exceeding 1 mW, the results demonstrate the potential of direct epitaxial growth of high-quality III-V materials on silicon. According to imec, the work provides a pathway to the development of cost-effective, high-performance optical devices for applications in data communications, machine learning, and AI. The lack of highly scalable, native CMOS-integrated light sources has been a major roadblock for the widespread adoption of silicon photonics. Hybrid or heterogeneous integration solutions such as flip-chip, micro-transfer printing, or die-to-wafer bonding involve complex bonding processes or the need for expensive III-V substrates that are often discarded after processing. This not only increases costs, but also raises concerns about sustainability and resource efficiency. For that reason, the direct epitaxial growth of high-quality III-V optical gain materials selectively on large-size silicon photonics wafers remains a highly sought-after objective. A 300 mm silicon wafer containing thousands of GaAs devices (left) with a close-up of multiple dies (middle) and a scanning electron micrograph of a GaAs nano-ridge array after epitaxy (right). Courtesy of imec. The large mismatch in crystal lattice parameters and thermal expansion coefficients between III-V and silicon materials inevitably initiates the formation of crystal misfit defects, which are known to deteriorate laser performance and reliability. Selective-area growth (SAG) combined with aspect-ratio trapping (ART) significantly reduces defects in III-V materials integrated on silicon by confining misfit dislocations within narrow trenches etched in a dielectric mask. “Over the past years, imec has pioneered nano-ridge engineering, a technique that builds on SAG and ART to grow low-defectivity III-V nano-ridges outside the trenches,” said Bernardette Kunert, scientific director at imec. This approach, she said, not only further reduces defects, but also allows for precise control over material dimensions and composition. The optimized nano-ridge structures typically feature threading dislocation densities well below 105 cm-2. “Now, imec exploited the III-V nano-ridge engineering concept to demonstrate the first full wafer-scale fabrication of electrically pumped GaAs-based lasers on standard 300 mm silicon wafers, entirely within a CMOS pilot manufacturing line,” Kunert said. Leveraging the low-defectivity GaAs nano-ridge structures, the lasers integrate InGaAs multiple quantum wells as the optical gain region, embedded in an in situ doped p-i-n diode and passivated with an indium gallium phosphide capping layer. Achieving room-temperature, continuous-wave operation with electrical injection is a major advancement, overcoming challenges in current delivery and interface engineering. The devices show lasing at ~1020 nm with threshold currents as low as 5 mA, slope efficiencies up to 0.5 W/A, and optical powers reaching 1.75 mW, showcasing a scalable pathway for high-performance silicon-integrated light sources. “The cost-effective integration of high-quality III-V gain materials on large-diameter silicon wafers is a key enabler for next-generation silicon photonics applications,” said Joris Van Campenhout, fellow silicon photonics and director of the industry-affiliation R&D program on Optical I/O at imec. “These exciting nano-ridge laser results represent a significant milestone in using direct epitaxial growth for monolithic III-V integration.” The project is part of a larger pathfinding mission at imec to push III-V integration processes towards higher levels of technological readiness, Campenhout said, from flip-chip and transfer-printing hybrid techniques in the near term, over heterogeneous wafer- and die-bonding technologies and eventually direct epitaxial growth in the longer term. The research was published in Nature (www.doi.org/10.1038/s41586-024-08364-2).