Investigating GaAs metamorphic lasers

Telecommunication is an important part of society and one of the ways data is transmitted is by sending light pulses down an optical fibre. Typically, semiconductor lasers emitting in the region between 1330nm and 1500nm are used with the current lasers being grown on InP substrates. However, GaAs substrates are preferred as they are less sensitive to temperature changes, available in larger sizes and cheaper in comparison to InP. Although GaAs is more favourable to use, optimal performance is usually limited to outside the telecommunication region due to differences between the lattice constants of the substrate and active region of the laser.

One way to overcome this is to create a virtual substrate with a chosen lattice constant by growing a lattice mismatched InGaAs lattice buffer layer onto GaAs. This procedure is known as metamorphic growth and allows GaAs substrates to be used with lattice constants that are similar to InP. Metamorphic GaAs lasers have been known for a while but are now starting to show performances which are commercially viable. Furthermore, metamorphic growth could also be used for lasers in other fields such as medical and environmental monitoring.

Recently, the Epitaxy and Physics of Nanostructures group at the Tyndall National Institute in Cork developed a novel metamorphic GaAs laser design. Grown by metalorganic vapour phase epitaxy, one heterostructure with active region of 3 quantum wells showed low threshold pulsed lasing with threshold density current of 127mA per QW at room temperature and continuous wave operation over 1300nm at 288K under various injection currents (further details in MOVPE metamorphic lasers and nanostructure engineering at telecom wavelengths). The next stage would be to find out more about the structure of the semiconductor laser as properties such as defects, strain and morphology can influence the performance of the laser.

This project is being conducted in conjunction with the EPSRC Photonic Integration and Advanced Data Storage Centre for Doctoral Training, PIADS CDT. A collaboration between multiple academic and industrial organisations including Queen's University Belfast and Tyndall National Institute, the CDT's remit is to solve current challenges in the field of data storage and transmission. This research falls into the PIADS CDT research theme of Ultra-reliable semiconductor lasers operating in hostile environments and atomic scale analysis techniques.
The project will use electron microscopy techniques such as Transmission Electron Microscopy, Scanning Electron Microscopy and Energy Dispersive electron spectroscopy. Computational software will be used to analyse the images. Overall, these techniques will provide information on the structures at the nanoscale, with the focus on chemical composition, defects and strain.

The aim of this project is to investigate the GaAs metamorphic samples grown and use the techniques to provide a comprehensive analysis at the atomic scale. The findings can then be linked to the optical properties of the laser and the growth procedure for optimisation. In turn, we hope to improve the laser performance in the range of 1300nm to 1550nm.

Academic
- The renewal will create 50 doctoral researchers with high level technical abilities and sophisticated managerial, leadership and personal effectiveness skills ready to take up employment in industry (with partners or beyond) or embark on academic careers.
- The programme will foster multidisciplinary perspectives in the cohorts which will allow them to address challenges either in research areas directly aligned to the PIADS CDT or beyond e.g. in ICT, Healthcare Technologies and sensing.
- Through the PIADS ecosystem academic staff and research groups will foster and form new collaborations leading to research outputs and impact, funding proposals and knowledge transfer.
- PIADS will provide career enhancing opportunities for its academic community, from established academics (advancement) to Early Career academics (supervisory experience and building research profile).
- PIADS will influence the delivery of other postgraduate programmes in the Universities by raising standards and expectations of the postgraduate experience through its cohort based training programme.
- The CDT will foster greater institutional collaboration through jointly awarded research degrees.

Industrial
- PIADS will bring together key companies who form a complete UK manufacturing supply chain for HAMR data storage technology.
- PIADS will drive the development and adoption of low-cost heterogeneous photonic integration technology that can be exploited not only in HAMR but also in multiple markets.
- The PIADS anchor tenant model will impact industry in multiple ways e.g. by facilitating co-creation of PhD/EngD projects, providing an ecosystem that links micro businesses and SMEs through to multinationals, and producing highly skilled doctoral researchers to meet recruitment needs for continued growth.

Societal
- PIADS Engagement & Outreach will continue to deliver its extensive programme of public engagement & outreach e.g. participation in European Researchers' Night, the N. Irish and Glasgow Science Festivals, the STEM Ambassador Programme, industry seminars and workshops and networking. These activities allow the cohorts and the public to interact with the science and technology of PIADS while respecting principles of Responsible Research and Innovation.

Economic
- PIADS will allow the industry partners to recruit skilled and qualified staff that support their respective plans for growth.
- PIADS will support UK economic activity in a sector that has 3X the average national productivity per worker.
- PIADS will support Seagate Technology in its plans to incorporate photonic integration into its current products thereby securing the future of some 1400 people in manufacturing and R&D, which contributes around £100M GVA p.a. to the UK economy in one of its most deprived areas.
- PIADS will engender the creation of an indigenous UK supply chain for low cost photonic integration technologies.
- PIADS will support the industrial partners to exploit outcomes related to their future market strategies, facilitating growth opportunities in a variety of sectors e.g. IQE, CST, KNT, Fraunhofer in ICT, Oxford Instruments, Yelo in scientific and engineering instrumentation, and Causeway Sensors and Cirdan Imaging in medical technology.