A hybrid silicon evanescent electroabsorption modulator
Yinghao Kuo, Huiwen Chen, and John E. Bowers
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Abstract: A new way to make high speed modulators using Si waveguides is demonstrated. The
hybrid silicon evanescent electroabsorption modulator with offset AlGaInAs quantum wells has an
extinction ratio over 10dB and modulation bandwidth over 16GHz.
©2007 Optical Society of America
OCIS codes: (250.4410) Modulators; (250.5300) Photonic integrated circuits; (250.7360) Waveguide modulators.
1. Introduction
Silicon3based modulators have attracted much attention with devices reported using the free carrier plasma
dispersion in Mach3Zehnder interferometric form [1,2] or with resonator structure [3,4] to increase the interaction of
light with the active material. Strained silicon also exhibits linear electro3optic refractive index modulation [5].
Recently electroabsorption modulator on silicon had been demonstrated based on the Franz3Keldysh effect in
strained SiGe [6]. Here we present our approach of integration of modulators into silicon using wafer bonded hybrid
silicon evanescent platform. The modulator described here can be integrated with lasers [7], amplifiers, and
photodetectors [8] using quantum well intermixing [9]. High performance integrated high speed transmitters should
be possible.
2. Device structure and fabrication
The silicon evanescent electroabsorption modulator (EAM) is a hybrid structure that consists of an offset multiple
quantum well (MQW) region bonded to a silicon waveguide fabricated on a silicon3on3insulator (SOI) wafer as
shown in Fig. 1. The III3V epitaxial structure is grown on an InP substrate. The structure is summarized in Table 1.
InGaAlAs is chosen as the MQW material because it has larger E
c
, which provides a stronger carrier confinement
and produce strong quantum confined stark effect (QCSE) with higher extinction ratio [10,11]. The MQW section
contains 10 wells and 11 barriers with photoluminance (PL) at 1478nm. The silicon waveguide was fabricated with
a height of 0.5Bm and slab thickness of 0.3Bm. The silicon waveguide has a width of 1.5Bm for passive segments,
and width of 0.8um under III3V mesa for higher optical confinement. The width of the III3V mesa for the absorber is
4Bm at the top InP cladding layer and 2Bm at the SCH and MQW layers to reduce the capacitance of the device
[11,12]. Figure 1b shows the transition between the passive silicon waveguide and the hybrid waveguide of the
EAM. The width of the III3V mesa is tapered from 0 to 2Bm over a length of 60Bm to increase the coupling
efficiency and to minimize reflection. The center of the absorption region is kept with width of 4Bm to avoid
laterally affect the optical mode and reduce the voltage drop at InP cladding. The contact electrode pads are
designed to be 100Bm apart from center to center to use a standard GSG RF probe for high speed testing. The hybrid
device has a total length around 400Bm with 100Bm absorber and two 60Bm long tapers.
0.1 *m n. i. d. In
0.520
Al
0.160
Ga
0.320
As, 0.06%, 1.30 *m SCH 5
Bonding layer
Super lattice
N Contact
MQW
(λ
PL
~1.48 *m)
SCH
Cladding
P Contact
Layer
10 nm N – 3e18 InP 8
0.11 *m N – 3e18 InP 6
1.5 *m P – 1e18 InP 2
N – 3e18
N – 3e18
n. i. d.
n. i. d.
P – 1e17
P – 1e19
Doping
7.5 nm InP (2x)
7
7.5 nm In
0.85
Ga
0.15
As
0.327
P
0.673
(2x)
7 nm In
0.470
Al
0.200
Ga
0.330
As, 0.40%, 1.19 *m (11x)
4
11 nm In
0.590
Al
0.080
Ga
0.330
As, +0.41%, 1.55 *m (10x)
0.15 *m In
0.520
Al
0.160
Ga
0.320
As, 0.06%, 1.30 *m 3
0.1 *m In
0.53
Ga
0.47
As 1
Thickness Material and Composition
0.1 *m n. i. d. In
0.520
Al
0.160
Ga
0.320
As, 0.06%, 1.30 *m SCH 5
Bonding layer
Super lattice
N Contact
MQW
(λ
PL
~1.48 *m)
SCH
Cladding
P Contact
Layer
10 nm N – 3e18 InP 8
0.11 *m N – 3e18 InP 6
1.5 *m P – 1e18 InP 2
N – 3e18
N – 3e18
n. i. d.
n. i. d.
P – 1e17
P – 1e19
Doping
7.5 nm InP (2x)
7
7.5 nm In
0.85
Ga
0.15
As
0.327
P
0.673
(2x)
7 nm In
0.470
Al
0.200
Ga
0.330
As, 0.40%, 1.19 *m (11x)
4
11 nm In
0.590
Al
0.080
Ga
0.330
As, +0.41%, 1.55 *m (10x)
0.15 *m In
0.520
Al
0.160
Ga
0.320
As, 0.06%, 1.30 *m 3
0.1 *m In
0.53
Ga
0.47
As 1
Thickness Material and Composition
Fig. 1. Schematic diagrams of (a) device cross section
and (b) hybrid waveguide and metal contacts.
Table 1. III3V epitaxial layer structure.
a1925_1.pdf
OThC1.pdf
OFC/NFOEC 2008