|dc.contributor.author||Dereshgi, Sina Abedini||en_US
|dc.description||Cataloged from PDF version of article.||en_US
|dc.description||Thesis (M.S.): Bilkent University, Department of Electrical and Electronics Engineering, İhsan Doğramacı Bilkent University, 2017.||en_US
|dc.description||Includes bibliographical references (leaves 82-90).||en_US
|dc.description.abstract||Metal-insulator (MI) stacks are one of the most studied nanoscale devices of the
recent decade. These structures have opened a new door to endless photonic
applications ranging from solar cells to waveguides and polarizers. The main attribute
of metal-insulator stacks is possibility of scaling down device dimensions
with them that is the main trend in photonic and electronic technology nowadays.
The conventional photonic structures require very high thicknesses where novel
photonic devices can show many arti cial properties by tailoring speci cally designed
metal-insulator cells also known as metamaterials.
In this thesis, we will investigate some metal-insulator absorber stacks with capability
of highly con ning light speci cally for photodetection. The near-infrared
part of the electromagnetic spectrum is problematic in photocurrent generation
due to the fact that conventional narrow band gap PN photodiodes fail to function
in room temperature. Adding to this predicament is their large dimensions.
Some of these problems are addressed in this thesis. First a plasmonic MIM structure
is studied with random nanoparticles obtained by dewetting in the top layer
which con nes the incident light in the plasmonic MIM cavity and gives rise to
high absorption through surface plasmon polariton excitation in the bottom lossy
metal. Several materials are investigated in order to engineer best absorbers with
the focus on absorption in the bottom metal which is critical for photodetection.
Our simulations and experimental results demonstrate over 90 percent absorption
for most of the visible and near-infrared region. The absorption in the bottom
metal in a structure comprised of chromium-aluminum oxide-silver nanoparticles
(bottom to top) reaches 82 percent at 850 nm. After obtaining appropriate
NIR absorption, an MIMIM photodetector is designed and fabricated where another
insulator-metal layer is added to the bottom of the previous absorber. The
formerly reported plasmonic photodetectors put the burden of absorption and photocurrent path on the same MIM structure putting restrictions on device design.
In our proposed structure, however, tunneling MIM photocurrent junction
is used which shares only its top metal with the top absorbing MIM. The main
advantage of this structure is that it separates the absorption and photocurrent
parts of the photodetector, making separate optimization of each MIM possible.
The best structure which is silver-hafnium oxide-chromium-aluminum oxide-silver
nanoparticles (top to bottom) demonstrates a peak photoresponsivity (from nonradiative
decay of surface plasmon polaritons) of 0.962 mA/W at 1000 nm and a
dark current of only 7 nA in a bias of 50 mV. Our results demonstrate approximately
two orders of magnitude enhancement in photoresponsivity compared to
previously reported MIMIM photodetectors.
In another attempt to obtain perfect absorbers for visible and near-infrared regions,
we put forth an MIMI absorber. In this work, the contribution of metal
layers is studied in detail and material choice is discussed. Our optimization process
suggests a versatile method for designing perfect absorbers. Transfer matrix
method as well as FDTD simulations are used to optimize thicknesses. Furthermore,
in order to shed light on material selection, impedance matching of the
waves in the multilayer media to free space is proposed for the extraction of ideal
metal permittivity values and comparing them to existing metals. Our experimental
result of a tungsten-aluminum oxide-titanium-aluminum oxide (bottom
to top) structure illustrates over 90 percent absorption for wavelength range of
400 nm to 1642 nm which is the highest perfect absorption bandwidth reported
in similar MIMI structures to the best of our knowledge.||en_US
|dc.description.statementofresponsibility||by Sina Abedini Dereshgi.||en_US
|dc.format.extent||xvii, 94 leaves : illustrations, charts (some color) ; 29 cm||en_US
|dc.subject||Broadband perfect absorption||en_US
|dc.title||Metal-insulator multistacks for absorption and photodetection||en_US
|dc.title.alternative||Emilim ve foto algılama için metal-yarı iletken çoklu istifleri||en_US
|dc.department||Department of Electrical and Electronics Engineering||en_US