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Hong Kong team grows bufferless III-V lasers on silicon


Lasers can sustain room-temperature and low-threshold lasing in the 1.5 μm band, say researchers

Researchers from the Hong Kong University of Science and Technology (HKUST) have reported what they believe to be the world's first 1.5 μm III-V lasers directly grown using MOCVD on standard 220 nm SOI (silicon-on-insulators) wafers without buffer, potentially paving an opening to the 'holy grail' for silicon photonics research. Previous demonstrations required non-industry-standard bulk Si or thick SOI wafers.The research findings were published online in Optica in February 2020.

In other conventional approaches of integrating III-V lasers on Si in the literature, thick III-V buffers up to a few micrometers are used to reduce the defect densities, which posts challenges for efficient light interfacing between the epitaxial III-V lasers and the Si-based waveguides.

The research team led by Lau Kei-May of HKUST's Department of Electronic and Computer Engineering and Han Yu devised a novel growth scheme to eliminate the requirement of thick III-V buffers and thus promoted efficient light coupling into the Si-waveguides. The bufferless feature points to a fully integrated Si-based photonic integrated circuits.

Lau's group at HKUST's Phonics Technology Centre has endeavoured to integrate III-V materials and functionalities on mainstream silicon wafers for over a decade. This work is part of their project on monolithic integration of III-V lasers on silicon.

Their new method saw them first devising a growth scheme to directly grow high quality III-V materials on the industry-standard 220 SOI platforms. Then, they characterised and evidenced the excellent crystalline quality of these epitaxial III-V materials through transmission electron microscopy and photoluminescence measurements.

The team designed and fabricated the air-cladded laser cavities based on numerical simulations and they eventually tested the devices which showed that the lasers could sustain room-temperature and low-threshold lasing in the technologically important 1.5 μm band under optical excitation.

The demonstration leads to the possibility and potential to monolithically integrate III-V lasers on the industry-standard 220 nm SOI wafers in an economical, compact, and scalable way.

Lau said: "If practically applied, our technology could enable a significant improvement of the speed, power consumption, cost-effectiveness, and functionality of current Si-based integrated circuits. Our daily electronic devices, such as smartphones, laptops and TVs - basically everything connected to the internet - will be much faster, cheaper, using much less power and multi-functional."

Han added: "The next step of our research will be to design and demonstrate the first electrically-driven 1.5 μm III-V lasers directly grown on the 220 nm SOI platforms, and devise a scheme to efficiently couple light from the III-V lasers into Si-waveguides and thereby conceptually demonstrate fully-integrated Si-photonics circuits."

'Bufferless 1.5  µm III-V lasers grown on Si-photonics 220  nm silicon-on-insulator platforms' by Yu Han et al; Optica Vol. 7, Issue 2, pp. 148-153 (2020)

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