Tensile Strain in Ge-on-Silicon Microbridges

  • Niamh Mulholland

Student thesis: Master of Philosophy


Over the past few decades, we have seen a surge in demand for increased computational power. The greatest bottleneck to computer performance is, and remains, the limitations of IC electrical interconnects. Optical interconnects are a promising solution to overcoming the fundamental limitations of their electrical counterparts. Many of the key components for an optical system have been realized, however, a fully integrated light source is the final missing piece. The development of an efficient, CMOS-compatible light source opens doors for a range of photonic integrated circuit applications. Ge has proven itself a promising candidate for a Si-compatible source technology. The small energy difference between the conduction band minima and valence band maxima allows for a pseudo-direct bandgap that can be achieved through bandgap-engineering. Recent literature reports high-tensile strain in Ge of up to 5.4% as well as lasing in optically pumped Ge. The realisation of a Ge laser that can be fully integrated into an optical interconnect system depends on the fabrication of a high-Q optical cavity with a low lasing threshold. While maximising tensile strain to create a pseudo-direct bandgap has been considered a key step toward creating an efficient Ge laser, it is also critical to be able to mitigate against various loss mechanisms to realise a practical device. In this thesis, I present the design, simulation and fabrication of tensiley-strained Ge microbridge structures. This work focuses on the optimisation of induced strain in Ge microbridges and discusses the varying effects of tensile strain and doping. Novel device designs from recent literature are compared, laying out a roadmap of future designs to achieve an efficient, easily integrable device.
Date of Award31 Dec 2021
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorMatthew Halsall (Supervisor) & Iain Crowe (Supervisor)


  • Microfabrication
  • Tensile strain
  • Photonics
  • Germanium
  • Silicon

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