A1GaN UV photodetectors : from micro to nano
Author
Bütün, Serkan
Advisor
Özbay, Ekmel
Date
2011Publisher
Bilkent University
Language
English
Type
ThesisItem Usage Stats
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Show full item recordAbstract
The absorption edge of AlGaN based alloys can be tuned from deep UV
to near UV by changing the composition. This enables the use of the material in
various technological applications such as military, environmental monitoring
and biological imaging. In this thesis, we proposed and demonstrated various
UV photodetectors for different purposes. The multi-band photodetectors have
the unique ability to sense the UV spectrum in different portions at the same
time. We demonstrated monolithically integrated dual and four-band
photodetectors with multi layer structures grown on sapphire. This was achieved
through epitaxial growth of multi AlGaN layers with decreasing Al content. We
suggested two different device architectures. First one has separate filter and
active layers, whereas the second one has all active layers which are used as
filter layers as well. The full width at half maximum (FWHM) values for the
dual band photodetector was 11 and 22 nm with more than three orders of
magnitude inter-band rejection ratio. The self-filtering four band photodetector
has FWHMs of 18, 17, 22 and 9 nm from longer to shorter bands. Whereas
photodetector with separate filter layers has FWHMs of 8, 12, 11 and 8 nm,
from longer to shorter bands. The overall inter-band rejection ration was
increased from about one to two of magnitude after incorporating the passive
filter layers. The plasmonic enhancement of photonic devices has attracted much
attention for the past decade. However, there is not much research that has been
conducted in UV region. In the second part of this thesis, we fabricated nanostructures
on GaN based photodetectors and improved the responsivity of the
device. We have fabricated Al nano-particles on sapphire with e-beam
lithography. We characterized their response via spectral extinction
measurements. We integrated these particles with GaN photodetectors and had
enhancement of %50 at the plasmonic resonance of the nano-particles.
Secondly, we have fabricated sub-wavelength photodetectors on GaN coupled
with linear gratings. We had 8 fold enhancement in the responsivity at the
plasmonic resonance frequency of the grating at normal incidence. Numerical
simulations revealed that both surface plasmons and the unbound leaky surface
waves played a role in the enhancement. We, finally, conducted basic research
on the current transport mechanisms in Schottky barriers of AlGaN based
materials. Experiments revealed that the tunneling current plays a major role in
current transport. In addition incorporation, of a thin insulator between metalsemiconductor
interface reduces the undesired surface states thereby improving
the device performance.
Keywords
AlGaNGaN
Photodetector
Multi-band
Dual-band
MSM
Schottky
Plasmonics
Surface Plasmon Polariton
Grating
Nano-particle
Localized Surface Plasmon Resonance