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LT-GaAs Based Photoconductive Antenna Arrays
For Pulsed And CW Operation
M.Awad, M.Nagel and H.Kurz
Institute of Semiconductor Electronics, RWTH Aachen, 52074 Aachen, Germany
awad@iht.rwth-aachen.de
Abstract—We present a novel epitaxial lift-off technique
for the fabrication of THz antenna array structures on low
temperature grown (LT) GaAs. The radiated electric field
of the array shows an increase compared to single element
element emitters, due to the constructive interference of
the individual array elements in the emitter far-field. We
have demonstrated this emitter in pulsed THz operation,
however simulations have shown that this type of structure
can also be used for continuous wave (cw) THz generation.
I. Introduction
THz radiation, whether pulsed or continuous wave, has
found widespread application in the recent years and has
proven itself as a valuable tool for material characteriza-
tion and spectroscopy. New emerging THz imaging appli-
cations [1] have made this technology further attractive to
industry and the medical field. Therefore there exists on-
going interest to develop optimized THz emitter and detec-
tor structures. A promising way to increase the efficiency
of photoconductive devices is to increase the active area
through multiple elements arranged as an array. This type
of array structure has previously been demonstrated using
semi-insulating (SI) GaAs as the substrate material and
shows an increase of the emitted THz radiation [2]. This
increase is attributed to the constructive interference of
the radiation emitted from the individual array elements
in the far-field. The THz antenna structure presented is
fabricated on low-temperature grown (LT) GaAs using an
epitaxial lift-off technique described below.
II. Fabrication
The THz antenna array structure, shown in figure 1,
is fabricated on a multilayer substrate consisting of a SI-
GaAs layer, followed by a 100 nm AlAs layer,a so called
sacrificial layer and finally 500 nm layer of epitaxially
grown LT-GaAs. The semiconductor material between
consecutive array elements is etched away to avoid radia-
tive contributions resulting from carriers accelerating in
the reverse electric field between elements, thus causing
destructive interference in the far-field and a zero net ra-
diation. This etch step prevents the need for an isolation
layer and additional metalization to shield this area be-
tween elements from optical excitation. The array itself
consists of eleven inter-digitated electrode pairs, with each
electrode pair constituting one array element. The met-
alized array structure is lifted off the SI-GaAs layer by
etching the AlAs, yielding the antenna structure on a LT-
GaAs substrate, which can be mounted onto various types
Fig. 1. THz antenna array structure, White spaces between antenna
elements show the etched off semiconductor areas.
of substrates via van-der-Waals bonding.
III. Measurements
Two types of measurements were performed to charac-
terize the THz antenna array. For both measurements,
the THz detector was a 5µm dipole antenna fabricated on
LT-GaAs with a silicon lens used to focus the incident THz
beam onto the detector. The first type of measurement was
carried out in a conventional THz-TDS setup and shows
the antenna’s characteristics at various bias voltages and
optical excitation powers. Second, we measured the an-
tenna radiation pattern and compared it to a single ele-
ment antenna. Furthermore, this type of array structure
can be used in cw THz generation [3]
IV. Conclusion
We present a THz antenna array fabricated using an
epitaxial lift-off technique. This antenna structure can be
used for both, pulsed and cw THz generation. Finally we
show the antenna characteristics and radiation pattern.
References
[1] M. M. Awad and R. A. Cheville, “Transmission terahertz
waveguide-based imaging below the diffraction limit,” Applied
Physics Letters, vol. 86, no. 22, p. 221107, 2005.
[2] A. Dreyhaupt, S. Winnerl, T. Dekorsy, and M. Helm, “High-
intensity terahertz radiation from a microstructured large-area
photoconductor,” Applied Physics Letters, vol. 86, no. 12, p.
121114, 2005.
[3] D. Saeedkia, A. H. Majedi, S. Safavi-Naeini, and R. R. Man-
sour, “Analysis and design of photoconductive interdigitated pho-
tomixer/antenna for thz applications,” IEEE Journal of Quan-
tum Electronics, vol. 41, pp. 234–241, 2005.
