Optical studies of crystal phase heterostructures

Research output: ThesisDoctoral Thesis (compilation)

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Abstract

III-V semiconductors are commonly used for a variety of optical applications, such as LED based lights and solar sells. Most III-V semiconductors, such as GaAs and InP, exhibit the zinc-blende (zb) crystal structure, but in the form of nanowires it is also possible to create them in the wurtzite (wz) crystal structure. This allows for the creation of novel heterostructures consisting of the same compound, but different crystal structures, so called crystal phase or
polytype heterostructures. Unlike material heterostructures, these polytype heterostructures have atomically sharp interfaces with minimal strain. This could make them ideal candidates for a number of applications, such as single photon sources, and as an environment to study interesting physical phenomena such as electron crystals and quantum dots (Q-dots).
In this work I have used photoluminescence (PL) spectroscopy and photoluminescence excitation (PLE) spectroscopy to investigate a number of InP and GaAs polytype heterostructures. PL and PLE are non-invasive optical techniques that use absorption and emission of photons to gain information about a number of semiconductor properties, such as bandgap, band structure and the energy of impurity levels. The PL and PLE measurements of single, nanowires are combined with electron microscopy. This allows for the correlation of the morphology and crystal structure quality with the optical properties of the polytype heterostructures. Finally, the measured optical properties are correlated to numerical calculations of electronic structure.
This thesis consists of three papers. In paper I it is shown that the Fermi-level pinning at the semiconductor-air surface influences the perceived valence band offset between the wz and zb crystal structure in GaAs nanowires. In paper II the existence of a two dimensional electron gas at the wz-zb interface in modulation doped InP nanowires is demonstrated. Finally, paper III explores zb-GaAs Q-dots in narrow wz-GaAs nanowires. The existence of multiple Q-dot states is confirmed trough PLE, whose energies correlate with numerical calculations of the Q-dot energy levels. The results in this thesis pave the way towards the use of polytype heterostructures for the study of physical phenomena, such as electron crystals.
Original languageEnglish
QualificationDoctor
Awarding Institution
  • Lund University
Supervisors/Advisors
  • Pistol, Mats-Erik, Supervisor
  • Lehmann, Sebastian, Supervisor
  • Pryor, Craig E., Supervisor, External person
Award date2021 Oct 22
Place of PublicationLund
Publisher
Print ISBNs978-91-8039-002-6
Electronic ISBNs978-91-8039-003-3
Publication statusPublished - 2021 Sep 28

Bibliographical note

Defence details
Date: 2021-10-22
Time: 13:15
Place: Lecture hall Rydbergsalen, Department of Physics, Professorsgatan 1, Faculty of Engineering LTH, Lund University, Lund. Zoom: https://lu-se.zoom.us/j/62722309876?pwd=UEZHYlpJbFAwOU53VVNHTFgrNy85QT09
Passcode: 927587

External reviewer(s)
Name: Joyce, Hannah
Title: Dr.
Affiliation: University of Cambridge, United Kingdom.
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Subject classification (UKÄ)

  • Condensed Matter Physics

Keywords

  • III-V semiconductor nanowires
  • photoluminescence
  • photoluminescence excitation
  • polytype
  • crystal phase heterostructure
  • InP
  • GaAs
  • wurtzite
  • Fysicumarkivet A:2021:Geijselaers

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