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First laser grown on silicon substrate to advance silicon photonics

A world first for UCL in conjunction with The London Centre for Nanotechnology, Cardiff University and the University of Sheffield

 

A group of researchers from UCL Electronic & Electrical Engineering and the London Centre for Nanotechnology, working with colleagues at Cardiff University and the University of Sheffield in work funded by the UK Engineering and Physical Sciences Research Council (EPSRC) has demonstrated the first practical electrically driven 1300-nm wavelength quantum dot laser grown directly grown on a silicon (Si) substrate.

Silicon is the most widely used material for the fabrication of active devices in electronics. However, its indirect gap band structure makes it extremely hard to realise an efficient silicon-based light source. As the speed and complexity of silicon electronics increases it is becoming harder to interconnect large information processing systems using conventional copper electrical interconnects. There is, thus strongly growing interest in developing optical interconnects for use with silicon electronics leading to the research field of silicon photonics. The ideal light source for silicon photonics would be a semiconductor laser, for high efficiency, direct interfacing with silicon drive electronics and high-speed data modulation capability. To date, the most promising approach to a light source on silicon has been the use of wafer bonding to join direct gap band structure compound semiconductor laser material to a silicon substrate.

Direct epitaxial growth of compound semiconductor laser material on silicon would be an attractive route to full monolithic integration for silicon photonics. However, the large differences in crystal lattice constant between silicon and compound semiconductors cause dislocations in the crystal structure that have resulted in low efficiency and short operating lifetime for previously demonstrated semiconductor lasers on silicon. The UCL group has overcome these difficulties by developing special dislocation filtering layers, together with a quantum dot laser gain layer. This has enabled them to demonstrate an electrically driven 1,300 nm wavelength laser by direct epitaxial growth on silicon. The work, published today in Nature Photonics, has resulted in lasers with a low threshold current density of 62.5 A/cm2, a room-temperature output power exceeding 105 mW, lasing operation up to 120 oC, and over 3,100 hours of continuous-wave operating data collected, giving an extrapolated mean time to failure of over 100,000 hours (doi:10.1038/nphoton.2016.21).

Professor Huiyun Liu, leader of the epitaxy research that enabled the creation of these lasers in UCL Electronic & Electrical Engineering, said:

"The use of the quantum dot gain layer offers improved tolerance to residual dislocations relative to conventional quantum well structures for III-V devices monolithically grown on silicon. Our works on defect filter layers and III-V quantum dots have enabled us to create the first practical laser on a silicon substrate, with an extrapolated lifetime exceeding 100,000 hours. This work will lay the foundation for reliable and cost-effective silicon-based photonic–electronic integration"

Head of the Photonics Group in UCL Electronic & Electrical Engineering, Principal Investigator in the London Centre for Nanotechnology and Director of the EPSRC Centre for Doctoral Training in Integrated Photonic and Electronic Systems, Professor Alwyn Seeds, said:

"The techniques that we have developed permit us to realise the Holy Grail of silicon photonics - an efficient and reliable electrically driven semiconductor laser directly integrated on a silicon substrate. Our future work will be aimed at integrating these lasers with waveguides and drive electronics leading to a comprehensive technology for the integration of photonics with silicon electronics"

Bright field scanning transmission electron microscopy image of dislocation filter layers.

Bright field scanning transmission electron microscopy image of dislocation filter layers

Schematic of the layer structure of an InAs/GaAs quantum-dot laser on a silicon substrate.

Schematic of the layer structure of an InAs/GaAs quantum-dot laser on a silicon substrate.

A scanning electron microscope overview of whole III-V laser on silicon.

A scanning electron microscope overview of whole III-V laser on silicon.

 

 


 


 

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