Strain engineering of Ge/GeSn photonic structures

Millar, Ross W. (2017) Strain engineering of Ge/GeSn photonic structures. PhD thesis, University of Glasgow.

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Abstract

Silicon compatible light sources have been referred to as the \holy grail" for Si
photonics. Such devices would give the potential for a range of applications;
from optical interconnects on integrated circuits, to cheap optical gas sensing
and spectroscopic devices on a Si platform. Whilst numerous heterogeneous
integration schemes for integrating III-V lasers with Si wafers are being pursued,
it would be far easier and cheaper to use the epitaxial tools already in
complementary-metal-oxide-semiconductor (CMOS) lines, where Ge and SiGe
chemical vapour deposition is used in a number of advanced technology nodes.
Germanium is an effcient absorber, but a poor emitter due to a band-structure
which is narrowly indirect, but by only 140 meV. Through the application of
strain, or by alloying with Sn, the Ge bandstructure can be engineered to
become direct bandgap, making it an effcient light emitter. In this work,
silicon nitride stressor technologies, and CMOS compatible processes are used
to produce levels of tensile strain in Ge optical micro-cavities where a transition
to direct bandgap is predicted. The strain distribution, and the optical
emission of a range of Ge optical cavities are analyzed, with an emphasis on
the effect of strain distribution on the material band-structure. Peak levels of
strain are reported which are higher than that reported in the literature using
comparable techniques.
Furthermore, these techniques are applied to GeSn epi-layers and demonstrate
that highly compressive GeSn alloys grown pseudomorphically on Ge virtual
substrates, can be transformed to direct bandgap materials, with emission
>3 m wavelength { the longest wavelength emission demonstrated from GeSn
alloys. Such emission is modeled to have a good overlap with methane absorption
lines, indicating that there is huge potential for the such technologies
to be used for low cost, Si compatible gas sensing in the mid-infrared.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Subjects: T Technology > T Technology (General)
Colleges/Schools: College of Science and Engineering > School of Engineering
Funder's Name: Engineering & Physical Sciences Research Council (EPSRC)
Supervisor's Name: Paul, Dr. Douglas
Date of Award: 2017
Depositing User: Dr Ross Millar
Unique ID: glathesis:2017-7918
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 06 Feb 2017 12:12
Last Modified: 14 Jun 2018 09:34
URI: http://theses.gla.ac.uk/id/eprint/7918

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