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Intro
to THz detector technology
Terahertz (THz) frequency band
offers many unique opportunities, such as applications in security screening,
bio, medical, pharmaceutical industry. However, lack of affordable and
sensitive room temperature detectors for the THz band hinders the development
of the various technologies.
Related
previous research by Sherwin group
77 K UCSB Terahertz Antenna
Coupled Inter-subband Terahertz (TACIT) Detector
Previously, Sherwin group
had made a sensitive narrowband, tunable Terahertz detector based on
inter-subband transition of quantum wells. However, due to the nature of its
excitation mechanism, it required cooling with liquid Nitrogen.
Beginning
of the 300 K UCSB THz detector project
Using similar device structure
to the TACIT at 77K, but by introducing a non-saturable absorber instead of
inter-subband transitions of the quantum wells, we could make room
temperature THz detectors. One such example is bulk electron plasmon.
Absorb
THz with twin-slot dipolar antennas --> transfer the energy
into active area of the transistor --> excite 3D electrons -->
measure the change of Source-Drain resistance. The antenna was
designed to work for horizontally polarized THz radiation. A photoconductive
signal was expected.
Recent
experimental results
In experiments,
however, our detector responds to vertical polarization only (at
300 K), and generates photovoltaic signal. E&M simulation later showed
that we are indeed coupling to the vertical polarization via “surface plasmonic
mode” supported by metal-insulator-metal gaps in our unique detector
structure. The resulting responsivity from this unexpected detection mode is
better than commercial pyroelectric detectors, but not better than Schottky
diodes, the current state-of-the-art.
These results are published on Appl. Phys. Lett. 92, 253508
(2008). Here are the data (pdf), from
which we reason that the responsivity is due to excitation of 3D electron
plasmon.
Search
for detection mechanisms
Although our detector works,
the exact operating principle is not understood. Theoretical and experimental
exploration for possible detection mechanism is ongoing.
Next
generation devices
Design and fabrication of next
generation devices is ongoing.
(Figure) UCBS THz detector sees
the water absorption through 60 cm of air in the lab.
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