Epitaxial and cavity design optimisation for the next generation of InP semiconductor laser devices

Abstract

Various indium phosphide-based laser diode devices have been studied over the course of this project with the aim of improving their performance for the cutting edge of modern applications. In the first part of the study, the epitaxial structure was studied, in particular, the doping concentration across the device, the effect of changing the doping concentration in each layer and how this could be optimised for high power applications. Using simulations, the structure was designed with a new doping profile and this design was then manufactured at Sivers Photonics and the test results are presented here showing that the new design succeeds in reducing the thermal roll-off leading to better performance though this better performance is only realised for devices operating at high currents but represents worse performance for low current operation. In the course of this study, the effect of thyristor breakdown was studied and due to the fact that a lot of the devices in the first batch were not able to reach high power due to this effect, a new design was proposed and again fabricated at Sivers Photonics which reduced this effect and was overall a success at high powers.

The second main challenge studied in this thesis is that of linewidth. Three different measurement techniques were studied and the advantages and disadvantages of each were considered before settling on the self-heterodyne method of measurement. Two different sets of devices were measured. One set had a partially corrugated grating along the cavity of different percentages and the linewidth results showed that shorter grating cavities resulted in narrower linewidth for devices of the same epitaxial design with equivalent threshold current, slope efficiency and power. The second set of devices had various phase shifts added along the cavity in order to provide a more uniform carrier and photon density distribution to reduce the effect of spatial hole burning, and this resulted in a lower linewidth at higher powers where spatial hole burning is an issue. Using these designs, devices can be fabricated where narrow linewidth at high powers is a requirement.

Thesis is embargoed until 31 December 2029.

Date of Award	Dec 2024
Original language	English
Awarding Institution	Queen's University Belfast University of Glasgow
Sponsors	Engineering & Physical Sciences Research Council
Supervisor	Anthony E Kelly (Supervisor)