Daisy Shearer


Postgraduate Research Student
MPhys Physics

Biography

Daisy Shearer is a PhD candidate in experimental condensed matter physics at the University of Surrey’s Advanced Technology Institute, working within the photonics and quantum sciences group. Her PhD research focuses on semiconductor spintronics and electron spin in InSb-based nanodevices for quantum technology applications.

She holds an integrated master’s degree in physics with first-class honours from the University of Surrey (2014-2018) where her master’s research project involved working in R&D at the Centre for Integrated Photonics developing High-Speed Electroabsorption Modulated Lasers (EMLs) for long-haul telecommunications.

She is a passionate researcher, science communicator, and educator with a drive to make STEM more accessible and inclusive, particularly disabled and neurodivergent people.

University roles and responsibilities

  • Physics PGR Outreach Ambassador (2020-present)
  • Staff Neurodiversity Network Co-chair (2021-present)
  • FEPS Student Forum Neurodiversity Representative (2022)
  • Postgraduate Student Ambassador- Widening Participation, Outreach, and Marketing (2020-present)
  • Physics EDI Committee PGR Representative (2018-2022)
  • FEPS Education and Public Engagement Module Design Team (2021-2022)

    My qualifications

    2014-2018
    MPhys Physics

    Dissertation: 'Investigating the DC Opto-electrical & Large Signal Characteristics of Electroabsorption Modulated Lasers'
    University of Surrey

    Research

    Research interests

    Research projects

    Indicators of esteem

    • Early Career Physics Communicator Award

      Institute of Physics, June 2021

    • Three Minute Thesis People’s Choice Award

      University of Surrey, June 2021

    • ATI Research Laureate Award

      Advanced Technology Institute, University of Surrey, February 2022

    Main current research questions:

    • Can we utilise the spin-orbit interaction in InSb and related III-V semiconductors to create spin-polarized currents?

    • Can we make a truly 100% spin-polarized current that can be propagated within materials in a useful way?

    • In what ways can we use spin-polarized currents for quantum metrology and other technology applications?

    • What is the optimum quantum point contact geometry for spin polarization?

    • Can direct-write fabrication methods help advance R&D of semiconductor devices?

    • Are hybrid semiconductor-superconductor devices suitable candidates for next-generation qubits?

    • Have we actually observed Majorana fermions or do we just think we have?

    • How can we physically create topological qubits in solid-state materials?

    My teaching

    My publications

    Publications

    The III-V narrowgap semiconductor InSb has properties such as low effective mass, high mobility, and strong spin-orbit coupling which make it an ideal material for spintronics. Recently there have been numerous device schemes that have been proposed for generating spin polarised currents for spin injection in quantum technologies. At the heart of these schemes is the quantum point contact (QPC) which requires nanoscale lithography and gated structures. Here we present a complete fabrication toolkit that employs focused ion beam (FIB) lithography as a flexible direct-write technique for rapid prototyping of QPCs. Two approaches for fabricating QPCs have been explored. The first method involves defining QPCs using direct etch writing of InSb quantum wells. A FIB assisted XeF2 chemistry has been used to form side gates with air gaps. The second technique uses FIB assisted deposition to form a siloxane gate dielectric, as well as direct-write of metalization using platinum to form split top gates. Compatibility of InSb with these processes has been confirmed by post-fabrication measurements of the electronic properties using Shubnikov de Haas and quantum Hall. The versatility of this direct-write technique makes it ideal as a rapid device prototyping tool.

    InSb is a III-V narrow-gap semiconductor with properties such as low effective mass, high mobility, and strong spin-orbit coupling making it an ideal material for applications such as spintronics mid-infrared photonics, and nanoelectronics. InSb quantum wells can be made by growing an InSb/InAlSb structure on a Ga substrate using molecular beam epitaxy. However, it is notoriously difficult to fabricate nanodevices from InSb/InAlSb quantum wells due to factors such as its low thermal budget and the production of non-volatile by-products in conventional etching processes, leading to unwanted deposition of material onto the material surface. Current wet and dry etching techniques take a long time and require expensive lithography masks to make new devices, slowing the development of optimised nanodevices.We investigate focused ion beam (FIB) lithography as a "rapid prototyping" fabrication technique to create semiconductor nanodevices from InSb quantum wells. FIB methods have the advantage of being relatively quick and "maskless", making them ideal for use in the research environment as new iterations of device design can be made quickly and different etching chemistries and electrical properties can be tested in-situ. A variety of Xe plasma FIB parameters were tested to optimise the feature resolution and etching quality of milled trenches at low temperatures. The XeF2 gas-assisted etching process was also studied as an alternative to the Cl2 chemistry that is typically employed for dry etching of InSb. Cross-sections and profiles of the trenches indicate that the XeF2 etch yields superior trench smoothness and mills material from the surface at a much higher rate. This method was also less prone to deposition of unwanted material onto the surface of the sample. This high-resolution fabrication method can be used for the rapid development and optimisation of individual nanoscale devices before mass production.