Preparation of InP-SiO2 3D photonic crystals

Article abstract of DOI:10.1016/j.physb.2005.01.399

Fabricated artificial opal templates and low pressure metal-organic chemical-vapor deposition have been used to infill the voids within opals and optimized the growth parameters. Scanning electron microscopy images, X-ray diffraction and reflection spectra results show that the InP is homogeneously distributed inside the opals, with high crystalline quality. The filling ratios of InP in the voids is about 12.8% and the photonic band gap is shifted to higher wavelength as a result of the high contrast of dielectric constants when InP is introduced which are in agreement with theoretical calculations.

Full text of DOI:10.1016/j.physb.2005.01.399

ARTICLE IN PRESS
Physica B 363 (2005) 1–6
www.elsevier.com/locate/physb
Preparation of InP–SiO2 3D photonic crystals
Ã
Tan Chunhua , Fan Guanghan, Zhou Tianming, Li Shuti, Sun Huiqing
Institute of Opto-electronic Materials and Technology, South China Normal University, Zhongshan Street, Guangzhou 510631,
People’s Republic of China
Received 11 July 2004; received in revised form 12 January 2005; accepted 13 January 2005
Abstract
Fabricated artificial opal templates and low pressure metal-organic chemical-vapor deposition have been used to infill
the voids within opals and optimized the growth parameters. Scanning electron microscopy images, X-ray diffraction
and reflection spectra results show that the InP is homogeneously distributed inside the opals, with high crystalline
quality. The filling ratios of InP in the voids is about 12.8% and the photonic band gap is shifted to higher wavelength
as a result of the high contrast of dielectric constants when InP is introduced which are in agreement with theoretical
calculations.
r 2005 Elsevier B.V. All rights reserved.
PACS: 81.15.Gh; 78.65.Jd; 77.90.+k
Keywords: Artificial opals; Photonic band gap; Photonic crystal; Metal-organic chemical-vapor deposition; Scanning electron
microscopy; Spectacular reflectivity
1. Introduction
light-emitting diodes, optical switches and tunable
filters. Since Yablonovich [1] suggested the idea of
photonic bands, there has been an increasing
interest in studying the photonic band gap (PBG)
structures in one-, two-, and three-dimensional
(1D, 2D, 3D) systems. Now, it has achieved great
success in fabricating 1D and 2D PCs. However,
the realization of photonic crystals for optical or
near infrared (IR) frequencies is still a major
technological challenge.
Photonic crystal (PC) is the name given to a
structure that possesses periodic dielectric constant
with a length scale of the same order as the
wavelength of the electromagnetic radiation.
Because photonic crystals can control the flow of
photons, it has many applications in low-loss wave
guides, optical cavities, zero threshold microlasers,
Synthetic opals made by means of sedimenta-
tion and ordering of SiO2 nanospheres have been
shown to be excellent candidates to build up 3D
Ã
Corresponding author. Tel.: 86 02085211435;
fax: 86 02085210809.
E-mail address: tch2000@163.com (T. Chunhua).
0921-4526/$ - see front matter r 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.physb.2005.01.399

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T. Chunhua et al. / Physica B 363 (2005) 1–6
PCs in the near-infrared-visible range [2–8]. Opals
have been proven to form a FCC lattice and
demonstrated a pronounced stop band in trans-
mission and reflectance spectrum [9]. However, the
resultant refractive index contrast between silica
and air (1.5:1) is weak, natural and artificial opal
do not exhibit a complete photonic gap, since its
stop bands for different in the Brillouin zone do
not overlap. Infilling the air voids within opals
with higher index semiconductor can suppress the
density of photonic states and improve the
photonic properties, even to produce a full PBG
material. Some work on semiconductor infilled
opals has been reported [10–14].
In this paper, we present an experimental
procedure designed to grow high-quality InP in
the opal voids, using metal-organic chemical-
vapor deposition (MOCVD). The homogeneous
distribution of the high ꢀ (ꢀ ¼ 12:7) guest material
in the low ꢀ host achieved by this method gives rise
to enhanced photonic crystal properties as has
been proved by enhanced photonic reflectance
measurements. The aim of this work is to provide
a foundation for fabricating 3D PCs devices.
samples present opalescence colors, which come
from the Bragg diffraction effects of the ordered
silica solid dielectric structure.
Before the opal photonic crystals are filled with
a precursor, it is desirable to sinter them. The
sintering process strengthens the opals and forms
the necks to connect every sphere with its
neighbors; the sintering process also permits to
control the opal void volume for subsequent
semiconductor infilling, and induces connected
network topology, allowing the removal of the
template by acid etching. The sintering took place
at 650 1C for 3 h in N2 ambient.
The InP was grown in the opal by the use of a
low pressure-MOCVD (LP-MOCVD) in a hor-
izontal reactor of the EMCORE (GS/3200) at a
pressure of 60 torr and a growth temperature of
550 1C. Palladium-purified hydrogen was used as
the carrier gas, trimethylindium (TMIn) was used
as the group III source, and phosphine was used as
the group V reactants.
Prior to growth, the samples were heated to
temperatures of up to 700 1C in the reactor under a
flow of H2 gas to remove moisture, grease and
besmirch, followed by a nucleating process that
the sources are decomposed to nucleate in a low
temperature (380 1C) and low flux of sources.
Because it is believed that deposition begins with
nucleation at defects on the surface of silica balls
before nucleus grows. The growth temperature is
lower than that normally employed in InP
MOCVD, which is due to the catalytic nature of
the silica surface exposed to TMIn, and this
surface-driven reactions often result in growth at
temperatures considerably lower than those
used in conventional MOCVD. Low-pressure is
necessary to drive sources diffusion into the
voids, and accordingly improve the infilling
ratio of the InP. During the growth process,
phosphine (450 ccm) was passed through the
reactor without interrupt, however TMIn
(180 ccm) was passed for 1 min then interrupted
for 3 min, and each cycle was for 4 min. With the
above cycle being repeated 20 times, higher
loading of InP can be achieved.
2. Experimental
The monodispersed (o5%) opal spheres were
fabricated following the Stober–Fink–Bohn pro-
cess. The hydrolysis of tetraethoxysilane (TEOS)
and later polymerization of Si–O chains in an
ethanol medium with ammonium hydroxide as a
catalyst is used, with sphere sizes varying from 200
to 600 nm by controlling the hydrolysis conditions.
There are a few methods to assemble order
colloidal crystal from monodispersed opal spheres,
such as natural sedimentation [15], electrophoresis
[16], centrifugation [7], solvent vaporization, etc.
For the need to infill InP by MOCVD, we
assembled the opal photonic crystal templates in
an FCC arrangement on GaAs substrate (151 off
the (1 0 0) plane towards the (0 1 1) direction) by
means of solvent vaporization. The steps involved
are: make opal spheres to be colloidal suspension
in ethanol, then dip the GaAs substrate into
suspension about 10 h, after ethanol is vaporized,
the suspensions are dried to form a film. The
After InP growth, the samples were heated to
690 1C in order to improve the semiconductor
crystallization and to allow diffusion of InP inside

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T. Chunhua et al. / Physica B 363 (2005) 1–6
3
the void structure. The experiments were carried
out to arrange different opal samples.
3. Characterization
Scanning electron microscopy (SEM) micro-
graphs were taken to study the morphology and
distribution of the InP grown inside the opals
using a Philips XL-30-ESEM-FEG instrument
operating at 15.0 or 20.0 kV. Fig. 1 corresponds
to an internal (1 1 1) family surfaces of opals
(sphere size d ¼ 250 nm) without infilling InP.
Figs. 2 and 3 show the details of the surface and
cleaved edge of a sample infilled with InP. In this
sample, InP crystals can be clearly seen on the
sphere surfaces, distinguished from the sphere
surfaces of the bare opal (Fig. 1). The SEM
images show that the InP is not only covering the
sphere surfaces but also infilling the interstitials
between the silica spheres. The phases in the
sample were detected by a D/max-3C X-ray
diffraction meter (XRD) with Ni-filtered Cu Ka
radiation (U ¼ 40 kV; I ¼ 100 mA) at a scanning
rate of 41/min. Fig. 4 is the XRD spectra of
Fig. 2. SEM image of a 0.5 mm  0.5 mm area of infiltrated opal
surface.
InP–SiO2 photonic crystals, which is in agreement
with the standard spectrum of InP, showing that
InP is of good quality and the distribution is very
homogeneous in the matrix. From the SEM
images, it can be seen that the InP surface is
smooth, indicating that the growth of the InP-
wetting layer is independent of the local character-
istics of the opal template. Maybe owing to the
fact that the procedure employed in this work is
more closely related to that employed under
atomic layer epitaxy conditions. As a consequence,
the 3D periodicity of the template is inherited by
the guest material, which is in good agreement
with the opal-InP composites optical feature.
The most direct way to measure the photonic
stop band behaviors is by optical reflectance.
Photonic crystal optical properties of bare and
InP infilled crystals were proved by means of
specular reflectance measurements in a UV-2550
UV–VIS–NIR spectrophotometer using plane
white light from a tungsten, holographic grating
as the spectroscope with a resolution of 0.2 nm, the
slit width is 2.0 nm and a photomultiplier tube as
the detector was used, the diameter of the
detecting spot is 2 mm. Fig. 5 shows specular
reflectance spectra from the (1 1 1) surface at 901
Fig. 1. SEM image of internal (1 1 1) facet of a bare opal. Inset
is the enlarged image of the same sample.

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T. Chunhua et al. / Physica B 363 (2005) 1–6
Fig. 3. SEM image of a cleaved edges of the sample infiltrated opal of magnifying 30 000 doubles. The inset is the same sample of
magnifying 10 000 doubles.
Indium Phosphide
refractive index materials provokes a shift of the
Bragg reflections towards higher wavelengths. The
result indicates that the InP is the homogeneous
distribution of the voids between opal spheres,
which is in agreement with the SEM images. For
Bragg reflections arise from the 3D order in the
samples and the shift of the (1 1 1) optical band is
only possible if a homogeneous distribution of the
InP infilled exists.
1500
1400
1300
1200
1100
1000
900
800
700
600
500
400
300
200
100
0
These optical characterization results can be
explained using Bragg law in the air:
20
30
40
50
60
15
2-Theta - Scale
File:XUJING031204-1(25).raw - Type: 2Th alone- Start:15.000˚ - End:66.000˚
-Step: 0.025˚ - Step time:0.5 s-Temp.: 25˚C(Room)- Time Started:
0 s - 2-Theta: 15.000˚ - Theta:5.000˚ - Display Operations: Import
2d
sin y ¼ l,
(1)
ð111Þ
32-0452 (*)- Indium Phosphide- InP- Y:87.45 % -dxby:1.0000 -WL: 1.54060
- Cubic - I/Ic PDF 1.0 -
but in the dielectric, the law should be modified
by [17]
Fig. 4. XRD spectra of InP–SiO2 photonic crystals.
1=2
lc ¼ 2dð111Þ ðꢀav À cos2 yÞ
,
(2)
where d(111) is the distance between crystallines
planes in the (1 1 1) direction. In this work, d
incidence angle (perpendicular to the surface) for
bare and InP infilled opals made up to 250 nm
spheres (10 layers). In Fig. 5, we observed the
Bragg reflection peaks coming from the coherent
scattering of light caused by the crystalline planes
of submicrometric opal spheres. One can notice
that the maximum peak of the bare opal is at
502 nm. However, the InP infilled opal is 540 nm.
Thus, we can conclude that the infilling with high
¼
ð111Þ
0:816a (a is the diameter of the opal spheres) for
the FCC structure, y is the angle between the
incident radiation and the sample (1 1 1) surface
(y ¼ 901), ꢀav is the average dielectric constant of
the composite, which can be approximated by the
expression:
ꢀav ¼ f ꢀ
þ f 0ꢀInP þ f 00ꢀair,
(3)
SiO2

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4. Conclusions
In this paper, a technique in which the opal was
infiltrated with InP by LP-MOCVD is introduced,
aiming at the fabrication of large-area high-
performance InP photonic crystal. The InP was
proved to be of high quality by SEM and
reflectance spectroscopy. The photonic crystal
properties of the samples is enhanced with the
InP infiltrated.
InP-opal
40.000
20.000
bare-opal
400.00
600.00
500.00
λ (nm)
Acknowledgements
Fig. 5. Specular reflectance for a bare opal (dashed line) and
the same opal infiltrated with InP.
This work was supported by the National
Advanced Materials Committee of China and the
National Nature Science Foundation of China.
where f, f 0; f 00 are the filling ratios of silica
(f ¼ 0:74), InP and air in the voids, respectively
(f 0 þ f 00 ¼ 0:26). It can be easily seen from
expression (2) that InP-infilled samples present
higher average dielectric constant. With ꢀav
increasing, lc shifts towards longer wavelengths.
So, it can be concluded that infilled samples
should present Bragg reflections at higher
wavelengths when compared with those coming
from bare ones. Experimental results shown
here are in good agreement with these con-
siderations.
According to Eqs. (1) and (2), the amount of
InP can be estimated. We have calculated that the
filling ratios of InP in the voids is about 12.8%.
In Fig. 5, we noticed that the intensity coming
from the opals-infiltrated InP is larger than that of
bare opals. The enhancement of the photonic
crystal properties in InP infilled samples is due to
the consideration that a low ꢀ matrix causes a large
increase in the scattering strength ꢀr of the periodic
composite. Since InP has a very high dielectric
constant (ꢀ ꢀ 12:7), even low InP loads yields a
substantial increase of ꢀav:
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