London, England--For the first time, an electrically pumped quantum-dot (QD) laser emitting at a telecom wavelength (1305 nm in this case) as been grown directly on a silicon substrate.1 The device was developed at University College London (UCL) and the London Centre for Nanotechnology.
The achievement will help enable fabrication of telecom-wavelength lasers on silicon -- a goal of many who want to create silicon-based photonic circuits with integrated lasers for data communications. Previously, the best approach to integrate telecom-wavelength semiconductor lasers with silicon photonics has been the use of wafer-bonding to join compound-semiconductor laser materials to a silicon substrate.
Direct growth of compound semiconductor-laser materials on silicon would be an attractive route to full integration for silicon photonics. However, the large differences in the crystal lattice constant between silicon and compound semiconductors cause dislocations in the crystal structure that result in low efficiency and short operating lifetimes for semiconductor lasers.
The UCL group has overcome these difficulties by developing layers that prevent these dislocations from reaching the laser layer, together with a QD laser-gain layer. This has enabled them to demonstrate a 15-mW-emitting electrically pumped 1300-nm-wavelength laser by direct epitaxial growth on silicon.
In earlier related work done in 2009, the group, working with the EPSRC National Centre for III-V Technologies, demonstrated the first QD laser on a germanium substrate by direct epitaxial growth. The 25-mW-emitting laser is capable of continuous operation at temperatures up to 70 °C.
"The use of the quantum dot gain layer offers improved tolerance to residual dislocations relative to conventional quantum well structures," says Huiyun Liu of UCL. "Our work on germanium should also permit practical lasers to be created on the Si/Ge substrates that are an important part of the roadmap for future silicon technology."
"Our future work will be aimed at combining these lasers with waveguides and drive electronics leading to a comprehensive technology for the integration of photonics with silicon electronics," says Alwyn Seeds of the London Centre for Nanotechnology.
REFERENCE:
1. Huiyun Liu et al., Nature Photonics (2011): doi:10.1038/nphoton.2011.120; Published online 12 June 2011.
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John Wallace | Senior Technical Editor (1998-2022)
John Wallace was with Laser Focus World for nearly 25 years, retiring in late June 2022. He obtained a bachelor's degree in mechanical engineering and physics at Rutgers University and a master's in optical engineering at the University of Rochester. Before becoming an editor, John worked as an engineer at RCA, Exxon, Eastman Kodak, and GCA Corporation.