Fabrication of electrically contacted plasmonic Schottky
nanoantennas on silicon
Mohammad Alavirad
1,2
, Anthony Olivieri
2
, Langis Roy
3
, and Pierre Berini
2,4,5,
*
1
Department of Electronics, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario K1S 5B6, Canada
2
Centre for Research in Photonics, University of Ottawa, 25 Templeton Street, Ottawa, Ontario K1N 6N5, Canada
3
Department of Electrical, Computer and Software Engineering, University of Ontario Institute of Technology,
2000 Simcoe Street North Oshawa, Ontario L1H 7K4, Canada
4
School of Electrical Engineering and Computer Science, University of Ottawa, 800 King Edward Avenue, Ottawa,
Ontario K 1N 6N5, Canada
5
Department of Physics, University of Ottawa, 150 Louis Pasteur, Ottawa, Ontario K1N 6N5, Canada
*Corresponding author: berini@eecs.uottawa.ca
Received December 24, 2017; accepted March 7, 2018; posted online April 28, 2018
We fabricate Schottky contact photodetectors based on electrically contacted Au nanoantennas on p-Si for
the plasmonic detection of sub-bandgap photons in the optical communications wavelength range. Based on
a physical model for the internal photoemission of hot carriers, photons coupled onto the Au nanoantennas
excite resonant plasmons, which decay into energetic “hot” holes emitted over the Schottky barrier at the
Au/p-Si interface, resulting in a photocurrent. In our device, the active Schottky area consists of Au/p-Si contact
and is very small, whereas the probing pad for external electrical interconnection is larger but consists of Au/Ti/
p-Si contact having a comparatively higher Schottky barrier, thus producing negligible photo and dark currents.
We describe fabrication that involves an electron-beam lithography step overlaid with photolithography. This
highly compact component is very promising for applications in high-density Si photonics.
OCIS codes: 240.6680, 250.5403.
doi: 10.3788/COL201816.050007.
Plasmonic nanoantennas have become important
photonic components for several applications involving
the conversion of light from free-space to small sub-
wavelength volumes. The behavior of metals at optical
frequencies is different from the microwave regime, and
this creates differences between optical antennas and
microwave antennas
[1,2
]. Well-designed metallic structures
having small dimensions, narrow gaps, and sharp corners
produce significant local optical field enhancement
and, consequently, strong enhancement of light–matter
interaction. Conversely, larger structures have better
scattering-to-extinction cross-section ratios and better re-
sponses in the far-field. Optical nanoantenna designs must
trade-off these properties
[3]
. Nanoscale monopoles, dipoles,
and bowties are three of the most popular types of optical
antennas. In most cases, Au and Ag are used as the metals
for the antennas, typicall y on a glass, indium tin oxide
(ITO), or Si substrate. The range of applications of these
types of antennas is very broad: biosensing
[4,5]
, photodetec-
tion
[6]
, spectroscopy and imaging
[7]
, and waveguiding
[8]
are
some examples.
The electric near-fields produced by optical antennas
can be of much greater intensity than the incident electric
fields
[9]
, so the photodetection volume can shrink, leading
to faster devices with compelling signal-to-noise character-
istics
[10]
. Mousavi et al. investigated a surface plasmon po-
lariton (SPP) photodetector based on the enhancement of
electric near-fields in low-defe ct, low-doped In
0.53
Ga
0.47
As
detection volumes located in the gaps of an array of metal
dipole antennas
[11]
; significant enhancement in responsiv-
ity was attributed to the dipoles. The 3 dB electrical
bandwidth of the device was estimated based on its resis-
tor-capacitor (RC) rise time and the hole transit time
through the detection volume for the cases of conventional
and ballistic transport and was found to range from ∼0.7
to 4 THz. Monopole arrays were also investigated for pho-
todetection based on internal photoemission (IPE)
[9]
. The
systems investigated consist of Au nanowires on Si
covered by H
2
O and a thin adlayer, representing a bio-
chemical coating aiming towards biosensing applications.
The resonance excited on such antennas by perpendicu-
larly incident light polarized along their axis is dipolar
and comprised of an SPP waveguide mode propagating
along the length of the nanowires and reflecting from
the ends to form standing waves along the antenna
[12]
.
The waveguide mode excited on the nanowires is a mode
of an asymmetric metal stripe
[13]
.
The IPE mechanism for holes is sketched in Fig.
1. IPE
is a three-step process consisting of the photoexcitation
of hot (energetic) carriers in the metal, transport with
scattering of hot carriers towards the metal–Si interface,
and the emission of hot carriers over the Schottky barrier
into the semiconductor, where they are collected as the
photocurrent. IPE requires that the energy of the incident
photons hν (h is Planck’s constant and ν is the optical fre-
quency) be greater than that of the Schottky barrier Φ
B
.
This mechanism is useful for detection at energies below
the semiconductor bandgap E
g
.
COL 16(5), 050007(2018) CHINESE OPTICS LETTERS May 10, 2018
1671-7694/2018/050007(6) 050007-1 © 2018 Chinese Optics Letters