Abstract
A study of the structural and opto-electronic properties of state-of-the-art GaAs and InP quantum dot (QD) lasers is reported.A high resolution structural analysis allows a size anisotropy of commercial GaAs based QDs to be determined. A model to simulate the shape of the density of states is then developed which accurately reproduces low temperature PL and room temperature absorption spectra. This model is subsequently used to provide a measure of carrier lifetime and predict new properties of the QD laser materials. A study of both GaAs based quantum well and quantum dot lasers is made with regard to their high temperature performance (up to ~450 K) and resilience to harsh environments. Suggestions for improved future designs and epitaxial growth improvements for high temperature operation are deduced, and insights into the carrier distribution within the QD laser are discussed. Device reliability and resilience is also explored, with GaAs based QD lasers showing enhanced resilience.
For InP based QD lasers, a study of the lasing characteristics of broad area lasers as a function of cavity length is made with a view to exploring epitaxial processes such as ripening and QD deposition temperature, and structural design parameters such as number and separation of QD layers. Full coverage of the S, C, and L optical communications bands by these lasers is demonstrated, leading to the opportunity for multi-band amplifier components. The variation of peak gain with carrier density is reported for the first time for these materials, allowing the interplay of loss and carrier transport to be highlighted. Optimal laser designs are deduced and future avenues to explore in terms of epitaxy are discussed. Characteristic temperatures of 140 K are deduced highlighting suitability for commercial roll-out.
| Date of Award | Dec 2020 |
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| Original language | English |
| Awarding Institution |
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| Sponsors | Engineering & Physical Sciences Research Council |
| Supervisor | Richard Hogg (Supervisor), David Childs (Supervisor) & Robert Bowman (Supervisor) |