Transparent conductive oxides (TCOs) are gaining increasingly high research interest for integrated photonic devices due to the strong plasma dispersion effect and process compatibility with versatile optoelectronic platforms. In this perspective article, the authors gave a brief review of research efforts both on theoretical modeling and experimental demonstration of integrated photonic devices, especially on high-efficiency electro-optic modulators through the integration with plasmonics and silicon photonics. In addition, the authors discussed the challenge and opportunity associated with TCO photonic devices and the application in photonic integrated circuits (PICs) with emphasis on high mobility materials, high-speed E-O modulators, and large-scale integration. Finally, we conclude that collaboration with existing silicon photonics foundry is a necessary route to incorporate TCOs into existing PIC ecosystems.

1.
G. V.
Naik
,
V. M.
Shalaev
, and
A.
Boltasseva
, “
Alternative plasmonic materials: Beyond gold and silver
,”
Adv. Mater.
25
(
24
),
3264
3294
(
2013
).
2.
D. S.
Ginley
and
J. D.
Perkins
, in
Handbook of Transparent Conductors
edited by
D. S.
Ginley
(
Springer US
,
Boston, MA
,
2011
), pp.
1
25
.
3.
K.
Ellmer
, “
Past achievements and future challenges in the development of optically transparent electrodes
,”
Nat. Photonics
6
(
12
),
809
817
(
2012
).
4.
S.
Calnan
and
A. N.
Tiwari
, “
High mobility transparent conducting oxides for thin film solar cells
,”
Thin Solid Films
518
(
7
),
1839
1849
(
2010
).
5.
Business Research Insights
, see https://www.businessresearchinsights.com/market-reports/transparent-conducting-oxide-tco-glass-market-103811 for “
Transparent conducting oxide (TCO) glass market size, share, growth, and industry analysis by type (ITO coated glass, FTO coated glass, AZO coated glass) by application (flat panel display, solar battery & others) regional forecast from 2022 to 2028
” (
2023
).
6.
J.
Karlsson
and
A.
Roos
, “
Annual energy window performance vs. glazing thermal emittance—the relevance of very low emittance values
,”
Thin Solid Films
392
(
2
),
345
348
(
2001
).
7.
A.
Melikyan
,
T.
Vallaitis
,
N.
Lindenmann
,
T.
Schimmel
,
W.
Freude
, and
J.
Leuthold
, “A surface plasmon polariton absorption modulator,” in
Conference on Lasers and Electro-Optics 2010
(
Optica Publishing Group
,
2010
), p.
JThE77
.
8.
E.
Feigenbaum
,
K.
Diest
, and
H. A.
Atwater
, “
Unity-order index change in transparent conducting oxides at visible frequencies
,”
Nano Lett.
10
(
6
),
2111
2116
(
2010
).
9.
P.
Drude
, “
Zur Elektronentheorie der Metalle
,”
Ann. Phys.
306
(
3
),
566
613
(
1900
).
10.
M. Z.
Alam
,
I.
De Leon
, and
R. W.
Boyd
, “
Large optical nonlinearity of indium tin oxide in its epsilon-near-zero region
,”
Science
352
(
6287
),
795
797
(
2016
).
11.
E.
Li
and
A. X.
Wang
, “
Femto-Joule all-optical switching using epsilon-near-zero high-mobility conductive oxide
,”
IEEE J. Select. Top. Quantum Electron.
27
(
2
),
1
9
(
2021
).
12.
J.
Bohn
,
T. S.
Luk
,
C.
Tollerton
,
S. W.
Hutchings
,
I.
Brener
,
S.
Horsley
,
W. L.
Barnes
, and
E.
Hendry
, “
All-optical switching of an epsilon-near-zero plasmon resonance in indium tin oxide
,”
Nat. Commun.
12
(
1
),
1017
(
2021
).
13.
S.
Saha
,
B. T.
Diroll
,
J.
Shank
,
Z.
Kudyshev
,
A.
Dutta
,
S. N.
Chowdhury
,
T. S.
Luk
,
S.
Campione
,
R. D.
Schaller
,
V. M.
Shalaev
,
A.
Boltasseva
, and
M. G.
Wood
, “
Broadband, high-speed, and large-amplitude dynamic optical switching with yttrium-doped cadmium oxide
,”
Adv. Funct. Mater.
30
(
7
),
1908377
(
2020
).
14.
H. W.
Lee
,
G.
Papadakis
,
S. P.
Burgos
,
K.
Chander
,
A.
Kriesch
,
R.
Pala
,
U.
Peschel
, and
H. A.
Atwater
, “
Nanoscale conducting oxide PlasMOStor
,”
Nano Lett.
14
(
11
),
6463
6468
(
2014
).
15.
Q.
Gao
,
E.
Li
, and
A. X.
Wang
, “
Ultra-compact and broadband electro-absorption modulator using an epsilon-near-zero conductive oxide
,”
Photonics Res.
6
(
4
),
277
281
(
2018
).
16.
V. J.
Sorger
,
N. D.
Lanzillotti-Kimura
,
R.-M.
Ma
, and
X.
Zhang
, “
Ultra-compact silicon nanophotonic modulator with broadband response
,”
Nanophotonics
1
(
1
),
17
22
(
2012
).
17.
R.
Amin
,
R.
Maiti
,
Y.
Gui
,
C.
Suer
,
M.
Miscuglio
,
E.
Heidari
,
R. T.
Chen
,
H.
Dalir
, and
V. J.
Sorger
, “
Sub-wavelength GHz-fast broadband ITO Mach-Zehnder modulator on silicon photonics
,”
Optica
7
(
4
),
333
335
(
2020
).
18.
A.
Melikyan
,
N.
Lindenmann
,
S.
Walheim
,
P. M.
Leufke
,
S.
Ulrich
,
J.
Ye
,
P.
Vincze
,
H.
Hahn
,
T.
Schimmel
,
C.
Koos
,
W.
Freude
, and
J.
Leuthold
, “
Surface plasmon polariton absorption modulator
,”
Opt. Express
19
(
9
),
8855
8869
(
2011
).
19.
M. G.
Wood
,
S.
Campione
,
S.
Parameswaran
,
T. S.
Luk
,
J. R.
Wendt
,
D. K.
Serkland
, and
G. A.
Keeler
, “
Gigahertz speed operation of epsilon-near-zero silicon photonic modulators
,”
Optica
5
(
3
),
233
236
(
2018
).
20.
E.
Li
,
Q.
Gao
,
R. T.
Chen
, and
A. X.
Wang
, “
Ultracompact silicon-conductive oxide nanocavity modulator with 0.02 Lambda-cubic active volume
,”
Nano Lett.
18
(
2
),
1075
1081
(
2018
).
21.
E.
Li
,
B. A.
Nia
,
B.
Zhou
, and
A. X.
Wang
, “
Transparent conductive oxide-gated silicon microring with extreme resonance wavelength tunability
,”
Photonics Res.
7
(
4
),
473
477
(
2019
).
22.
P. R.
West
,
S.
Ishii
,
G. V.
Naik
,
N. K.
Emani
,
V. M.
Shalaev
, and
A.
Boltasseva
, “
Searching for better plasmonic materials
,”
Laser Photonics Rev.
4
(
6
),
795
808
(
2010
).
23.
A.
Boltasseva
and
H. A.
Atwater
, “
Low-loss plasmonic metamaterials
,”
Science
331
(
6015
),
290
291
(
2011
).
24.
Z.
Ma
,
Z.
Li
,
K.
Liu
,
C.
Ye
, and
V. J.
Sorger
, “
Indium-Tin-oxide for high-performance electro-optic modulation
,”
Nanophotonics
4
(
2
),
198
213
(
2015
).
25.
V. E.
Babicheva
,
A.
Boltasseva
, and
A. V.
Lavrinenko
, “
Transparent conducting oxides for electro-optical plasmonic modulators
,”
Nanophotonics
4
(
2
),
165
185
(
2015
).
26.
W.
Jaffray
,
S.
Saha
,
V. M.
Shalaev
,
A.
Boltasseva
, and
M.
Ferrera
, “
Transparent conducting oxides: from all-dielectric plasmonics to a new paradigm in integrated photonics
,”
Adv. Opt. Photonics
14
(
2
),
148
208
(
2022
).
27.
I.
Liberal
and
N.
Engheta
, “
Near-zero refractive index photonics
,”
Nat. Photonics
11
(
3
),
149
158
(
2017
).
28.
J.
Wu
,
Z. T.
Xie
,
Y.
Sha
,
H. Y.
Fu
, and
Q.
Li
, “
Epsilon-near-zero photonics: infinite potentials
,”
Photonics Res.
9
(
8
),
1616
1644
(
2021
).
29.
X.
Niu
,
X.
Hu
,
S.
Chu
, and
Q.
Gong
, “
Epsilon-near-zero photonics: A new platform for integrated devices
,”
Adv. Opt. Mater.
6
(
10
),
1701292
(
2018
).
30.
S.
Campione
,
M. G.
Wood
,
D. K.
Serkland
,
S.
Parameswaran
,
J.
Ihlefeld
,
T. S.
Luk
,
J. R.
Wendt
,
K. M.
Geib
, and
G. A.
Keeler
, “
Submicrometer epsilon-near-zero electroabsorption modulators enabled by high-mobility cadmium oxide
,”
IEEE Photonics J.
9
(
4
),
1
7
(
2017
).
31.
A. P.
Vasudev
,
J.-H.
Kang
,
J.
Park
,
X.
Liu
, and
M. L.
Brongersma
, “
Electro-optical modulation of a silicon waveguide with an “epsilon-near-zero” material
,”
Opt. Express
21
(
22
),
26387
26397
(
2013
).
32.
J.
Baek
,
J.-B.
You
, and
K.
Yu
, “
Free-carrier electro-refraction modulation based on a silicon slot waveguide with ITO
,”
Opt. Express
23
(
12
),
15863
15876
(
2015
).
33.
S.
Zhu
,
G. Q.
Lo
, and
D. L.
Kwong
, “
Design of an ultra-compact electro-absorption modulator comprised of a deposited TiN/HfO2/ITO/Cu stack for CMOS backend integration
,”
Opt. Express
22
(
15
),
17930
17947
(
2014
).
34.
Z.
Lu
,
W.
Zhao
, and
K.
Shi
, “
Ultracompact electroabsorption modulators based on tunable epsilon-near-zero-slot waveguides
,”
IEEE Photonics J.
4
(
3
),
735
740
(
2012
).
35.
A. O.
Zaki
,
K.
Kirah
, and
M. A.
Swillam
, “
Hybrid plasmonic electro-optical modulator
,”
Appl. Phys. A
122
(
4
),
473
(
2016
).
36.
C.
Huang
,
R. J.
Lamond
,
S. K.
Pickus
,
Z. R.
Li
, and
V. J.
Sorger
, “
A sub-λ-size modulator beyond the efficiency-loss limit
,”
IEEE Photonics J.
5
(
4
),
2202411
(
2013
).
37.
U.
Koch
,
C.
Hoessbacher
,
J.
Niegemann
,
C.
Hafner
, and
J.
Leuthold
, “
Digital plasmonic absorption modulator exploiting epsilon-near-zero in transparent conducting oxides
,”
IEEE Photonics J.
8
(
1
),
1
13
(
2016
).
38.
A. V.
Krasavin
and
A. V.
Zayats
, “
Photonic signal processing on electronic scales: Electro-optical field-effect nanoplasmonic modulator
,”
Phys. Rev. Lett.
109
(
5
),
053901
(
2012
).
39.
G.
Sinatkas
,
A.
Pitilakis
,
D. C.
Zografopoulos
,
R.
Beccherelli
, and
E. E.
Kriezis
, “
Transparent conducting oxide electro-optic modulators on silicon platforms: A comprehensive study based on the drift-diffusion semiconductor model
,”
J. Appl. Phys.
121
(
2
),
23109
(
2017
).
40.
Q.
Gao
,
E.
Li
, and
A. X.
Wang
, “
Comparative analysis of transparent conductive oxide electro-absorption modulators, [Invited]
,”
Opt. Mater. Express
8
(
9
),
2850
2862
(
2018
).
41.
W.-C.
Hsu
,
B.
Zhou
, and
A. X.
Wang
, “
MOS capacitor-driven silicon modulators: A mini review and comparative analysis of modulation efficiency and optical loss
,”
IEEE J. Select. Top. Quantum Electron.
28
(
3
),
1
11
(
2022
).
42.
N.
Kinsey
,
C.
DeVault
,
A.
Boltasseva
, and
V. M.
Shalaev
, “
Near-zero-index materials for photonics
,”
Nat. Rev. Mater.
4
(
12
),
742
760
(
2019
).
43.
I.
Liberal
and
N.
Engheta
, “
The rise of near-zero-index technologies
,”
Science
358
(
6370
),
1540
1541
(
2017
).
44.
O.
Reshef
,
I.
De Leon
,
M. Z.
Alam
, and
R. W.
Boyd
, “
Nonlinear optical effects in epsilon-near-zero media
,”
Nat. Rev. Mater.
4
(
8
),
535
551
(
2019
).
45.
G.
Briere
,
B.
Cluzel
, and
O.
Demichel
, “
Improving the transmittance of an epsilon-near-zero-based wavefront shaper
,”
Opt. Lett.
41
(
19
),
4542
4545
(
2016
).
46.
X.-T.
He
,
Z.-Z.
Huang
,
M.-L.
Chang
,
S.-Z.
Xu
,
F.-L.
Zhao
,
S.-Z.
Deng
,
J.-C.
She
, and
J.-W.
Dong
, “
Realization of zero-refractive-index lens with ultralow spherical aberration
,”
ACS Photonics
3
(
12
),
2262
2267
(
2016
).
47.
L.
Caspani
,
R. P. M.
Kaipurath
,
M.
Clerici
,
M.
Ferrera
,
T.
Roger
,
J.
Kim
,
N.
Kinsey
,
M.
Pietrzyk
,
A.
Di Falco
,
V. M.
Shalaev
,
A.
Boltasseva
, and
D.
Faccio
, “
Enhanced nonlinear refractive index in ε-near-zero materials
,”
Phys. Rev. Lett.
116
(
23
),
233901
(
2016
).
48.
A.
Capretti
,
Y.
Wang
,
N.
Engheta
, and
L. D.
Negro
, “
Enhanced third-harmonic generation in Si-compatible epsilon-near-zero indium tin oxide nanolayers
,”
Opt. Lett.
40
(
7
),
1500
1503
(
2015
).
49.
A.
Capretti
,
Y.
Wang
,
N.
Engheta
, and
L.
Dal Negro
, “
Comparative study of second-harmonic generation from epsilon-near-zero indium tin oxide and titanium nitride nanolayers excited in the near-infrared spectral range
,”
ACS Photonics
2
(
11
),
1584
1591
(
2015
).
50.
R.
Amin
,
R.
Maiti
,
C.
Carfano
,
Z.
Ma
,
M. H.
Tahersima
,
Y.
Lilach
,
D.
Ratnayake
,
H.
Dalir
, and
V. J.
Sorger
, “
0.52 V mm ITO-based Mach-Zehnder modulator in silicon photonics
,”
APL Photonics
3
(
12
),
126104
(
2018
).
51.
J.
Park
,
J.-H.
Kang
,
X.
Liu
, and
M. L.
Brongersma
, “
Electrically tunable epsilon-near-zero (ENZ) metafilm absorbers
,”
Sci. Rep.
5
(
1
),
15754
(
2015
).
52.
Y.
Yang
,
K.
Kelley
,
E.
Sachet
,
S.
Campione
,
T. S.
Luk
,
J.-P.
Maria
,
M. B.
Sinclair
, and
I.
Brener
, “
Femtosecond optical polarization switching using a cadmium oxide-based perfect absorber
,”
Nat. Photonics
11
(
6
),
390
395
(
2017
).
53.
E.
Li
,
Q.
Gao
,
S.
Liverman
, and
A. X.
Wang
, “
One-volt silicon photonic crystal nanocavity modulator with indium oxide gate
,”
Opt. Lett.
43
(
18
),
4429
4432
(
2018
).
54.
E.
Li
,
B.
Zhou
,
Y.
Bo
, and
A. X.
Wang
, “
High-speed Femto-Joule per bit silicon-conductive oxide nanocavity modulator
,”
J. Lightwave Technol.
39
(
1
),
178
185
(
2021
).
55.
W.-C.
Hsu
,
E.
Li
,
B.
Zhou
, and
A. X.
Wang
, “
Characterization of field-effect mobility at optical frequency by microring resonators
,”
Photonics Res.
9
(
4
),
615
621
(
2021
).
56.
W.-C.
Hsu
,
C.
Zhen
, and
A. X.
Wang
, “
Electrically tunable high-quality factor silicon microring resonator gated by high mobility conductive oxide
,”
ACS Photonics
8
(
7
),
1933
1936
(
2021
).
57.
W.-C.
Hsu
,
N.
Nujhat
,
B.
Kupp
,
J. F.
Conley
, and
A. X.
Wang
, “
On-chip wavelength division multiplexing filters using extremely efficient gate-driven silicon microring resonator array
,”
Sci. Rep.
13
(
1
),
5269
(
2023
).
58.
E.
Li
and
A. X.
Wang
, “
Theoretical analysis of energy efficiency and bandwidth limit of silicon photonic modulators
,”
J. Lightwave Technol.
37
(
23
),
5801
5813
(
2019
).
59.
Y.
Gui
,
M.
Miscuglio
,
Z.
Ma
,
M. H.
Tahersima
,
S.
Sun
,
R.
Amin
,
H.
Dalir
, and
V. J.
Sorger
, “
Towards integrated metatronics: Holistic approach on precise optical and electrical properties of Indium Tin Oxide
,”
Sci. Rep.
9
(
1
),
11279
(
2019
).
60.
F.
Fuchs
and
F.
Bechstedt
, “
Indium-oxide polymorphs from first principles: Quasiparticle electronic states
,”
Phys. Rev. B
77
(
15
),
155107
(
2008
).
61.
T.
Koida
,
Y.
Ueno
, and
H.
Shibata
, “
In2O3-based transparent conducting oxide films with high electron mobility fabricated at low process temperatures
,”
Phys. Status Solidi
215
(
7
),
1700506
(
2018
).
62.
A.
Chaoumead
,
H.-D.
Park
,
B.-H.
Joo
,
D.-J.
Kwak
,
M.-W.
Park
, and
Y.-M.
Sung
, “
Structural and electrical properties of titanium-doped indium oxide films deposited by RF sputtering
,”
Energy Procedia
34
,
572
581
(
2013
).
63.
E.
Sachet
,
C. T.
Shelton
,
J. S.
Harris
,
B. E.
Gaddy
,
D. L.
Irving
,
S.
Curtarolo
,
B. F.
Donovan
,
P. E.
Hopkins
,
P. A.
Sharma
,
A. L.
Sharma
,
J.
Ihlefeld
,
S.
Franzen
, and
J.-P.
Maria
, “
Dysprosium-doped cadmium oxide as a gateway material for mid-infrared plasmonics
,”
Nat. Mater.
14
(
4
),
414
420
(
2015
).
64.
B.
Zhou
,
E.
Li
,
Y.
Bo
, and
A. X.
Wang
, “
High-speed plasmonic-silicon modulator driven by epsilon-near-zero conductive oxide
,”
J. Lightwave Technol.
38
(
13
),
3338
3345
(
2020
).
65.
C.
Hoessbacher
,
Y.
Fedoryshyn
,
A.
Emboras
,
A.
Melikyan
,
M.
Kohl
,
D.
Hillerkuss
,
C.
Hafner
, and
J.
Leuthold
, “
The plasmonic memristor: A latching optical switch
,”
Optica
1
(
4
),
198
202
(
2014
).
66.
Y.
Huang
,
J.
Zheng
,
B.
Pan
,
L.
Song
,
K.-A.
Chen
,
Z.
Yu
,
H.
Ye
, and
D.
Dai
, “
High-bandwidth Si/In2O3 hybrid plasmonic waveguide modulator
,”
APL Photonics
7
(
5
),
51301
(
2022
).
67.
W.-C.
Hsu
,
N.
Nujhat
,
B.
Kupp
,
J. F.
Conley
,
H.
Rong
,
R.
Kumar
, and
A. X.
Wang
, “
Sub-volt high-speed silicon MOSCAP microring modulator driven by high mobility conductive oxide
,” arXiv:2308.16255 (
2023
).
68.
D. S.
Zemtsov
,
I. A.
Pshenichnyuk
,
S. S.
Kosolobov
,
A. K.
Zemtsova
,
D. M.
Zhigunov
,
A. S.
Smirnov
,
K. N.
Garbuzov
, and
V. P.
Drachev
, “
Plasmon-assisted Si-ITO integrated electro-optical rib-shape modulator
,”
J. Light. Technol.
41
,
6310
6314
(
2023
).
69.
M. G.
Wood
,
P. S.
Finnegan
,
K. M.
Musick
,
W. M.
Mook
,
C. D.
Nordquist
,
A. J.
Grine
, and
D. K.
Serkland
, “
Epsilon-near-zero modulators integrated on Si3N4 waveguides for operation shorter than 1μm
,” in
Frontiers in Optics 2023
(
2023
), No. JTu4A.79.
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