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@PHDTHESIS{Schneider:854625,
author = {Schneider, Daniel Stefan},
othercontributors = {Lemme, Max C. and Vescan, Andrei},
title = {{F}lexible two‑dimensional/three‑dimensional material
based photodetectors},
school = {Rheinisch-Westfälische Technische Hochschule Aachen},
type = {Dissertation},
address = {Aachen},
publisher = {RWTH Aachen University},
reportid = {RWTH-2022-09676},
pages = {1 Online-Ressource : Illustrationen, Diagramme},
year = {2021},
note = {Veröffentlicht auf dem Publikationsserver der RWTH Aachen
University 2022; Dissertation, Rheinisch-Westfälische
Technische Hochschule Aachen, 2021},
abstract = {1. Motivation, Goal and Task of the Dissertation
Multispectral sensors enable the precise identification of
unknown substances, undistorted by the human perception of
colors. This makes it possible to carry out contactless and
non‑destructive analyses for identification of hazardous
substances. Electrically tunable photodetectors based on
hydrogenated amorphous silicon (a‑Si:H)are alternatives to
image sensors that are based on photodiodes with integrated
color filters which are used for such analyses. A specific
vertical device structure allows sampling of a wide range of
spectral bands in a single photodetector without the need
for optical filters. The integration of two‑dimensional
(2D) materials with interesting electrical, mechanical, and
optical properties, such as graphene and (molybdenum
disulfide (MoS₂) into the multispectral sensors, opens the
opportunity to extend the wavelength responsivity of these
devices. This can overcome a significant limitation of
silicon technology which primarily detects the visible
region. As part of this PhD thesis, hybrid photodetectors
based on 2D/3D heterostructures were simulated, fabricated,
and characterized. Monolayer MoS₂ offers high absorptions
of up to $10\%$ in the visible part of the electromagnetic
spectrum. It is also suitable for the development of
high‑performance and highly flexible wearable electronics
(wearables) due to its good electrical properties. The
integration of MoS₂ in light sensors on flexible
substrates can enable the realization of ultra‑thin and
highly sensitive sensors which are also interesting for
Internet of Things. Standard substrates for semiconductors
can also be thinned out to achieve higher device
flexibilities, but the bearable strain for such
intrinsically rigid and brittle substrate is rather limited.
Here, metalsemiconductor‑metal photodetectors with MoS₂
absorbers of only a few atomic layers thick were fabricated
on foil substrates and characterized with respect to their
optoelectronic properties. 2. Major Scientific Contributions
In this PhD thesis, 2D materials were successfully
integrated into vertical multispectral sensors based on
a‑Si:H for the first time. These 2D/3D hybrid
photodetector structures with graphene electrodes as
transparent and conductive electrodes show an enhanced UV
responsivity compared to devices with conventional
transparent conductive oxide (TCO) layers. In addition,
electrical measurements under bending cycles have
demonstrated that graphene‑ optimized multispectral
sensors can be operated under repetitive tensile strain. In
contrast, reference TCO‑based devices failed after only a
few bending cycles. The maximum spectral responsivity of the
photodetectors can be tuned from 310 nm to 520 nm by varying
the applied bias. The quantum efficiency of the flexible
photodetectors could be further increased by using bilayer
graphene due to the reduction of sheet resistances. The
research results were presented at international conferences
(ESSDERC 2016 and DRC 2016)and published in a journal
(Nanoscale 2017). In a collaboration work with the
University of Siegen, MoS₂ layers were integrated into
vertical a‑Si:H photodetectors and led to a responsivity
up to the infrared range (~2 μm). The spectral
responsivities of about 50 mA/W were achieved at energies
below the bandgaps of the absorber layers which is
unexpected, but verified by several optical measurements.
This is likely attributed to absorption through defects in
the 2D material and at the interfaces. The extension of the
spectral sensitivity range can be activated by applying an
electric field. The results were published in the journal
ACS Photonics in 2019. Laterally arranged metal‑2D
semiconductor‑metal photodetectors with additional gate
contact were fabricated and characterized. The potentially
scalable fabrication of flexible light sensors on flexible
substrates with very high spectral responses in the blue
wavelength region has been demonstrated by using MoS₂
grown on sapphire wafer. An additional gate contact allows
the optimization of the photocurrent in contrast to standard
photoconductor structures. These light sensors can be used
especially for the detection of blue light hazard caused by
modern LED‑based light sources with a high blue light
content. Also, these photodetectors are resistant to
recurring tensile strain, thus their integration in future
wearables is achievable. The results on the 2D
photodetectors were published at the international
conferences (DRC 2019 and Graphene Week 2019) and in the
journal ACS Photonics in 2020.},
cin = {618710},
ddc = {621.3},
cid = {$I:(DE-82)618710_20170609$},
pnm = {QUEFORMAL - Quantum Engineering for Machine Learning
(829035) / GrapheneCore3 - Graphene Flagship Core Project 3
(881603) / Scalable MoS2 based flexible devices and circuits
for wireless communications / Skalierbare MoS2-basierte
flexible Bauelemente und Schaltkreise für drahtlose
Kommunikation (407080863) / BMBF-16ES1134 - Verbundprojekt:
Neuro-inspirierte Technologien der künstlichen Intelligenz
für die Elektronik der Zukunft - NEUROTEC - (BMBF-16ES1134)
/ DFG project 255449811 - SPP 1796: High Frequency Flexible
Bendable Electronics for Wireless Communication Systems
(FFLexCom) (255449811)},
pid = {G:(EU-Grant)829035 / G:(EU-Grant)881603 /
G:(GEPRIS)407080863 / G:(DE-82)BMBF-16ES1134 /
G:(GEPRIS)255449811},
typ = {PUB:(DE-HGF)11},
doi = {10.18154/RWTH-2022-09676},
url = {https://publications.rwth-aachen.de/record/854625},
}
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