Silicon based QD light sources and lasers

Realising efficient electrically-pumped lasers based on Si substrates is the transformative step that enables the unification of III-V based communications technology with Si data processing and memory electronics. We will demonstrate that high performance light emitting devices can be fabricated on Si substrates using an approach based on quantum dots (QDs). The successful outcome will provide the basis for cheaper and better Si-based optoelectronic integrated circuits, a key enabler for the Digital Economy, and provide potential solutions for the impending Si CMOS interconnect challenges (where the physical length and energy requirements of the connections between electronic elements limits processing performance). This project is expected to contribute to improving quality of life for consumers and to wealth creation, for example low-cost and increased complexity Si chips for next-generation computers and higher-capacity communication systems.
The problems we will address include the very different crystal lattice size, and the different temperature dependence of the lattice size, of Silicon (the basis for most electronics) and the majority of III-V semiconductors (the basis for most light emitting devices) and the low device power consumption requirements for densely integrated components.
The research will investigate how to manage the lattice mismatch across the silicon to III-V interface, introduce methods to filter out crystal defects that originate from this region of the device and will use an active layer that is relatively intolerant to any remaining defects generated by this interface.
We will investigate how to make devices that require small numbers of electrons and devices that lose a very small number of the photons generated by these electrons using, for example, a wide range of materials such as GaInP for the laser cladding for low optical loss and InGaAsN(Sb) to allow quantum mechanical tunnelling into a small number of lasing states hence minimising electron use. This will make the overall devices very energy efficient which is also necessary to avoid the generation of large amounts of waste heat that is difficult (and energy costly) to dissipate.
We will also demonstrate that it is possible to manufacture laser mirrors and waveguides to couple light between the laser and other optical devices, for example amplifiers.
We will liase with leading UK based companies that are ideally placed to exploit the immediate outcomes of our work and also interact with other academic groups, where further research is necessary before our advances can be fully exploited. One example is an optical imaging technique that will benefit from increased data acquisition speed, enhanced portability and reduced price of the devices we will produce to allow early diagnosis of, for example, skin cancer or retinal diseases causing blindness.

The results will have economic impact in a number of fields and over a range of different timescales. Most immediate will be the development of high efficiency lasers on Si for communication applications. These will be of benefit to a number of UK manufacturers, particularly IQE and Oclaro with whom we have strong links. The results of the project will be discussed with IQE and Oclaro and they will advise us on critical material and design issues and on the optimum way to proceed to maximise the commercial benefit to the UK. The benefits to IQE and Oclaro include the enhancement of their product range, allowing them to maintain competitiveness against other international companies. We also have links with other UK manufacturers and the UK semiconductor/laser community via the National III-V Centre.

Other outputs will have an economic impact on an intermediate and longer timescale and will require further development by academic groups to take them to the commercial stage. Devices designed for optical coherence tomography (OCT) will be assessed by a leading academic group and a series of iterative optimisations is planned before their final suitability is assessed. We believe that such devices have the potential to make a significant impact in the health imaging field. Long wavelength single photon emitters designed for quantum cryptography applications will be developed and supplied for assessment to Prof Gerald Buller (Heriot Watt), an expert in the field. We include a travel budget to allow our PDRAs to actively participate in these development processes to maximise interaction and benefit.

This project is expected to contribute to improving quality of life for consumers and to wealth creation, such as low-cost and complex Si chips for next-generation computers and higher-capacity communication systems. The impact on society will be through the enhanced performance of ICT platforms for the digital economy and the reduction in greenhouse gases and reduced energy usage of these platforms. This will be enabled by the development of laser and related photon sources integrated with Si photonics and electronics. Direct benefits include: the ability to fabricate fully integrated photonic circuits on Si, providing a solution for limited interconnectivity in future generations of microprocessors; and enabling freestanding remote sensors combined with processing electronics. This will provide improved performance and functionality and open up a number of new applications.

The project offers an excellent training opportunity for PhD students (we have a current industrial CASE studentship with Oclaro and other positions will be funded from DTA and DTC funds) and PDRAs both in terms of technical training, research skills, experience of the interface between ICT and the life sciences and exposure to commercial entities such as Oclaro and IQE.

We anticipate that immediate commercial exploitation will be through two main routes. First, through licensing of intellectual property and a programme of knowledge transfer to our project partners and to other industrial collaborators. Second, where substantial development is required to establish the value of an innovation, through spin-out activity. UCL, Cardiff, and Sheffield have devoted substantial resources in support of commercial exploitation of its research work. Intellectual property arising from the research will be managed with reference to an IP agreement formed at the beginning of the project.