Group fabricates quantum dot laser on silicon substrate

Electronics engineers have succeeded in fabricating a quantum dot laser directly on a silicon substrate, in what represents an important step for the integration of silicon electronics with photonics.

The work could eventually result in super-fast devices and infrastructure for the telecommunications industry.

As the speed and complexity of silicon electronics increases, it is becoming harder to interconnect large information processing systems using conventional copper electrical interconnects. For this reason the field of silicon photonics (the development of optical interconnects for use with silicon electronics) is becoming increasingly important.

To date, the most promising approach to a light source for silicon photonics has been the use of wafer bonding to join compound semiconductor laser materials from which lasers can be made to a silicon substrate.

Direct growth of compound semiconductor laser material on silicon would be an attractive route to full integration for silicon photonics. However, the large differences in crystal lattice constant between silicon and compound semiconductors cause dislocations in the crystal structure that result in low efficiency and short operating lifetime for semiconductor lasers.

A group at University College London (UCL) overcame these difficulties by developing special layers that prevent these dislocations from reaching the laser layer together with a quantum dot laser gain layer. This has enabled the group to demonstrate an electrically pumped 1,300nm wavelength laser by direct epitaxial growth on silicon. In a recent paper in Optics Express it reports an optical output power of more than 15mW per facet at room temperature.

Prof Alwyn Seeds, head of the Photonics Group in the UCL Department of Electronic and Electrical Engineering, said: ‘The techniques that we have developed permit us to realise the Holy Grail of silicon photonics — an efficient, electrically pumped, semiconductor laser integrated on a silicon substrate.

‘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.’