The first practical telecommunications laser monolithically grown on a silicon substrate
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"
- Research paper: Electrically pumped continuous-wave III–V quantum dot lasers on silicon
- SEE THE LIGHT: Why lasers are the future for the silicon chip
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For more information, please contact Professor Huiyun Liu (tel: +44 (0)20 7679 3983; e-mail: firstname.lastname@example.org or Professor Alwyn Seeds (tel: +44 (0)20 7679 7928; e-mail: email@example.com)
The following images of quantum dot lasers fabricated on a silicon substrate at UCL can be obtained by calling the Department of Electronic and Electrical Engineering on +44 (0)20 7679 3983 or by emailing firstname.lastname@example.org
Fabricated quantum dot on silicon laser. (a) Scanning electron microscope image of fabricated laser; (b) Photograph of an array of lasers on silicon mounted on copper heat-sink with gold wire bond connections.
About UCL Electronic & Electrical Engineering
UCL Electronic & Electrical Engineering was the first department of Electrical Engineering to be established in England and now comprises some 200 researchers working on topics in communications and information systems, electronic materials and devices, optical networks, photonics and sensors, systems and circuits, with turnover exceeding £16 million. It has consistently been rated among the top five UK Departments in its subject area in the UK Government's research evaluations.
About the London Centre for Nanotechnology
The London Centre for Nanotechnology, is a UK-based, multidisciplinary research centre forming the bridge between the physical and biomedical sciences. It was conceived from the outset with a management structure allowing for a clear focus on scientific excellence, exploitation and commercialisation. It brings together two world leaders in nanotechnology, namely UCL and Imperial College London, in a unique operating model that accesses the combined skills of multiple departments, including medicine, chemistry, physics, electronic and electrical engineering, biochemical engineering, materials and earth sciences, and two leading technology transfer offices.
About Cardiff University
Cardiff University is recognised in independent government assessments as one of Britain’s leading teaching and research universities and is a member of the Russell Group of the UK’s most research intensive universities. The 2014 Research Excellence Framework ranked the University 5th in the UK for research excellence. Among its academic staff are two Nobel Laureates, including the winner of the 2007 Nobel Prize for Medicine, University Chancellor Professor Sir Martin Evans. Founded by Royal Charter in 1883, today the University combines impressive modern facilities and a dynamic approach to teaching and research. The University’s breadth of expertise encompasses: the College of Arts, Humanities and Social Sciences; the College of Biomedical and Life Sciences; and the College of Physical Sciences and Engineering, along with a longstanding commitment to lifelong learning. Cardiff’s flagship Research Institutes are offering radical new approaches to pressing global problems.
About the University of Sheffield
With almost 27,000 of the brightest students from over 140 countries, learning alongside over 1,200 of the best academics from across the globe, the University of Sheffield is one of the world’s leading universities. A member of the UK’s prestigious Russell Group of leading research-led institutions, Sheffield offers world-class teaching and research excellence across a wide range of disciplines. Unified by the power of discovery and understanding, staff and students at the university are committed to finding new ways to transform the world we live in. In 2014 it was voted number one university in the UK for Student Satisfaction by Times Higher Education and in the last decade has won four Queen’s Anniversary Prizes in recognition of the outstanding contribution to the United Kingdom’s intellectual, economic, cultural and social life. Sheffield has five Nobel Prize winners among former staff and students and its alumni go on to hold positions of great responsibility and influence all over the world, making significant contributions in their chosen fields. Global research partners and clients include Boeing, Rolls-Royce, Unilever, AstraZeneca, Glaxo SmithKline, Siemens and Airbus, as well as many UK and overseas government agencies and charitable foundations.
About the Sheffield Department of Electronic and Electrical Engineering
The Department has 42 academic staff (including 17 Professors) and 50 research staff plus a dedicated team of 21 technical and 26 administrative support staff. The Department has a student community of approximately 500 undergraduate and postgraduate taught and research students. The Department at Sheffield is respected internationally for its many important contributions in the field of semiconductor and materials research including a world class ultra-high resolution aberration corrected electron microscopy facility.