I

Integration of InGaAs/GaAs Quantum well with Surface
Plasmon and Photonic Bandgap Structure and their effect
on its PL Emission




GAO HONGWEI

(M.Eng, DaLian University of Technology, China)



A THESIS SUBMITTED

FOR THE DEGREE OF DOCTOR OF PHILOSOPHY


DEPARTMENT OF ELECTRICAL AND COMPUTER
ENGINEERING



NATIONAL UNIVERSITY OF SINGAPORE


2014

I



DECLARATION





I hereby declare that the thesis is my original work and it has been written by me
in its entirety. I have duly acknowledged all the sources of information which
have been used in the thesis.



This thesis has also not been submitted for any degree in any university
previously.






Gao Hongwei

15 May 2014










II

Acknowledgements


First of all, I want to thank my supervisor, Professor Chua Soo Jin, for his
guidance. It is a great honor to be his PhD student. I learnt the importance of
attitude towards research and even towards life in general. His academic advice
both in doing experiment and in organizing research structure is highly
appreciated.
I would like to appreciate the help and support from Dr. Xia ng Ning, who offered
me the opportunity to work on exciting and interdisciplinary topics and provided
me the wonderful chance to finish my PhD degree. I appreciate all the advices,
time and ideas she contributed to help me finish my journey as a PhD student.
I gratefully acknowledge Dr. Teng Jinghua for offering me the opportunity to
learn and use the fabrication and characterization equipment in the Institute of
Materials Research and Engineering. I also thank Dr. Lu Jun and Mr. Tung Kar
Hoo Patrick for providing MBE grown samples.
I also want to express my appreciation to the support given by Mr. Tan Beng

Hwee and Ms. Musni our helpful laboratory officers.
Finally, I would like to thank my parents for their constant encouragement and
support during the course of this work.








III

Table of Contents
DECLARATION I
Acknowledgements II
Summary V
List of Figures VII
List of Tables XI
List of Publications XII
List of Abbreviations XIV
Chapter one: Introduction 1
1.1. General introduction of Plasmonics 1
1. 2. Introduction of photonic bandgap 13
1.3. Research motivation 17
1.4. Scope of thesis 19
Chapter 2: Theory 22
2.1. Principle of Surface Plasmon 22
2.11 Non-localized surface plasmon 29
2.12 Localized surface plasmon 30

2.2 Principle of Photonic bandgap structures 34
Chapter 3: Study on tuning SPs resonance wavelength by metallic nanohole structure and
metallic nanoparticle structure 45
3.1 Introduction 45
3.2 Tuning SPs resonance wavelength by Ag nanohole structure 45
3.2.1 Sample preparation 46
3.2.2 Results and discussion 47
3.2.3 Conclusions 52
3.3 Tuning SPs resonance wavelength by metallic nanoparticle structures 52
3.3.1 Introduction 52
3.3.2 Sample preparation 53
3.3.3 Results and discussion 56
3.3.4 Conclusions 67
3.4 Summary 67
Chapter 4: Coupling of SPR to InGaAs QW 69


IV

4.1 Introduction 69
4.2 Coupling of Surface Plasmon with InGaAs/GaAs Quantum Well Emission by Gold
Nanodisk Arrays 70
4.2.1 Introduction 70
4.2.2 Sample preparation 72
4.2.3 Results and discussion 75
4.2.4 Conclusions 81
4.3 Enhancement of GaAs/InGaAs Quantum Well Emission by disordered Gold
Nanoparticle Arrays 81
4.3.1 Introduction 81
4.3.2 Sample preparation 82

4.3.3 Results and Discussion 85
4.3.4 Conclusions 90
4.4 Summary 91
Chapter 5: Coupling of SPR and Photonic Bandgap to InGaAs QW Emission 93
5.1 Introduction 93
5.2 Sample preparation 94
5.3 Results and discussion 97
5.4 Conclusions 109
Chapter 6: Conclusion and future work 111
6.1 Conclusions 111
6.2 Suggestion of future work 113
References 115














V

Summary


Surface plasmon resonance (SPR) excited at the metal-dielectric interface has
been investigated for various applications in the Optoelectronics. Enhancing
photoluminescence intensity of InGaAs/GaAs quantum well (QW) system in the
near infrared (NIR) range by SPs is demonstrated for the first time.
In order to overcome the fabrication challenge of putting metal nanoparticles
close to the quantum well layer without affecting its quality, a 50 nm thin SiO
2
was introduced between the Au nanodisk arrays and GaAs surface. We fabricated
an ordered array of Au nanostructures with relatively large features to match the
InGaAs/GaAs QW emission wavelength. Without the SiO
2
layer and its lower
refractive index compared to GaAs, the Au nonodots would have to be much
smaller. By overlapping the SPs resonant wavelength with that of the QW
emission, a strong coupling was demonstrated, and more than 4-fold enhancement
of the PL intensity was achieved. To match the longer QW emission wavelength
and to further make the fabrication process easier, we studied the irregular array
of Au nanodisks on the InGaAs/GaAs QW system with the 50 nm SiO
2
layer. By
introducing the irregularity, the number of SPs modes was increased, which
induced a larger exit angle for coupling the light out. However, it also resulted in
poorer coupling of the field distribution with the Quantum Well, resulting in only
a 2-fold enhancement in the photoluminescence intensity obtained.
To achieve a stronger SP-QW coupling effect, a thin quantum well barrier is
desirable to allow the confined electromagnetic field caused by SP to couple more


VI


strongly with the QW. However, a thin quantum well barrier layer leads to a
poorer QW emission performance. To solve this problem, we report on a photonic
bandgap structure patterned on the thick quantum well barrier. The array of Au
nanodisk is placed into the holes of the photonic bandgap structure filled with a
15 nm SiO
2
layer. Thus the Au nanodisks are placed close to the InGaAs active
layer without sacrificing the thickness of the GaAs quantum well barrier layer,
which is very important for a practical device. With this design, a maximum 7.6-
fold enhancement in the photoluminescence intensity has been obtained.
All the experimental results were verified by numerical simulations.



VII

List of Figures

Figure 1.1Number of articles varying with year 4
Figure 1.2 Demonstration of generating SP with prism 5
Figure 1.3 Demonstration of generating SP with grating 5
Figure 1.4 (a) Sample structure of InGaN/GaN QW and excitation/emission of PL
measurement. (b) PL spectra of InGaN/GaN QWs coated with Ag, Al, and Au.
The PL peak intensity of uncoated InGaN/GaN QW at 470 nm was normalized to
1 9
Figure 1.5 (a) PL enhancement ratios at several wavelengths for the same sample
as in Figure 1.4(b). (Inset) Dispersion diagrams of surface plasmons generated on
Ag/GaN, Al/GaN, and Au/GaN surfaces. (b) Integrated PL enhancement ratios for
samples with Ag, Al, and Au are plotted against the thickness of GaN spacers.
The solid lines are the calculated values by the penetration depths 10

Figure 1.6 (a) Sample structure of dye doped polymer with both pump light and
emission light configurations. (b) PL spectra of Coumarin 460 on Ag, Au, and
quartz. The PL peak intensity of Coumarin 460 on quartz was normalized to
1 11
Figure 1.7 (a) Sample structure of CdSe nanocrystals on Au-coated quartz chips.
(b) PL spectra for CdSe nanocrystals on Au and quartz (Qz) 12
Figure 1.8 (a) Sample structure of Si nanoparticles dispersed in SiO
2
media and
excitation/emission configuration of PL measurement. (b) PL spectra of Si/SiO
2

with Au, Al, and no metal layer 13
Figure 2.1 Definition of a planar waveguide geometry. The waves propagate
along the x-direction in a cartesian coordinate system 24
Figure 2.2 Geometry for SPP propagation at a single interface between a metal
and a dielectric 27
Figure 2.3 Sketch of a homogeneous sphere placed into an electrostatic field 31
Figure 2.4 One-dimensional photonic crystal made of an infinite number of planar
layers of thickness d 35
Figure 2.5 Band diagram for one-dimensional photonic crystal. The shaded areas
are the allowed bands. The diagram represents both TE and TM modes. For a 1D
photonic crystal, there are no complete bandgaps, i.e. there are no frequencies for
which propagation is inhibited in all directions. Values used: 
1
=2.33 (SiO
2
),

2

=17.88 (InSb) 38


VIII

Figure 2.6 The photonic band structure for the lowest-frequency modes of a
square array of dielectric (=8.9) vein (thickness 0.165a) in air. The blue lines are
TM bands and the red lines are TE bands. The left inset shows the high-symmetry
points at the corners of the irreducible Brillouin zone (shaded light blue). The
right inset shows a cross-sectional view of the dielectric function 40
Figure 2.7 Displacement fields of X-point TM modes for a square array of
dielectric (=8.9) veins in air. The color indicates the amplitude of the
displacement field, which is oriented in the z direction (out of the page). The
dielectric band is on the left, and the air band is on the right 42
Figure 2.8 Magnetic fields of X-point TE modes for a square array of dielectric
(=8.9) veins in air. The green dashed lines indicate the veins, and the color
indicateds the amplitude of the magnetic field, which is oriented in the z direction.
The dielectric band is on the left, and the sir band is on the right 42
Figure 3.1(a) SEM image of monolayer nanosphere on substrate 48
Figure 3.1(b) SEM image of monolayer nanosphere on substrate after dry
etching 48
Figure 3.1(c) SEM image of Ag hole arrays after removing the nanosphere 48
Figure 3.2 Experimental reflectance spectra for three samples. Triangular-shaped
black curve is for Ag holes with diameter of 375 nm on Si substrate; Dot shaped
red curve is for Ag holes with diameter of 340 nm on Si; Cross-line blue curve is
for Ag hole with diameter of 310 nm on Si 49
Figure 3.3 Simulated reflectance spectra for three samples. Triangular shaped
black curve is for Ag holes with diameter of 375 nm based on Si substrate; Dot
shaped red curve is for Ag holes with diameter of 340 nm; Cross-line shaped blue
curve is for Ag holes with diameter of 310 nm 50

Figure 3.4 Simulated SPs resonance wavelength for various diameter of Ag hole
arrays. Periodicity is 600 nm 52
Figure 3.5 Schematic structure of Sample A, B, C, and D 56
Figure 3.6 SEM image of Ag nanoparticle arrays on GaAs substrate in low
amplitude. Inset: SEM image of Ag nanoparticle arrays in high amplitude.
Periodicity is 430 nm, particle diameter is around 260 nm 57
Figure 3.7 Measured (above) and simulated (below) reflectance spectrum of
Sample A. Periodicity is 430 nm, the diameter is around 260 nm 58
Figure 3.8 Measured (above) and simulated (below) reflectance spectrum of
Sample B. Periodicity is 430 nm, diameter is around 260 nm 60
Figure 3.9 Measured (above) and simulated (below) reflectance spectrum of
Sample C. Periodicity is 430 nm, diameter is around 260 nm 61


IX

Figure 3.10 Measured (above) and simulated (below) reflectance spectrum of
Sample D. Periodicity is 430 nm, diameter is around 260 nm 62
Figure 3.11 Dipole mode plasmonic resonance wavelength vs periodicity (radius
of circle-shape Au nanoparticle is 60 nm) 66
Figure 3.12 Dipole mode plasmonic resonance wavelength vs radius of circle-
shape Au nanoparticle arrays (periodicity if 430 nm) 67
Figure 4.1 Schematic illustration of ordered Au nanodisk arrays on InGaAs/GaAs
QW sample fabrication process 74
Figure 4.2 SEM image of Au nanodisk arrays formed on top of QW for Sample
A1 75
Figure 4.3 PL spectra of as-grown sample, Sample B1 (dished curve) and sample
with SiO
2
/Au nanodisk arrays, Sample A1 (solid curve) 76

Figure 4.4 Reflectance spectrum of Sample A1: Au nanodisk arrays on SiO
2
on
top of as-grown sample (PL ~945 nm) 78
Figure 4.5 Schematic illustration of simulated structure. Electric dipole source
(center at 945 nm, FWHM of 60 nm) is 20 nm below GaAs surface. SiO
2

thickness is 50 nm, Au nanodisk arrays period is 280 nm, radius is 70 nm, and
thickness is 10 nm 80
Figure 4.6 Spectrum of E intensity variations with wavelength for Sample
A1 80
Figure 4.7 SEM image of irregular Au nanodisk arrays for Sample B2 84
Figure 4.8 SEM image of ordered Au nanodisk arrays for Sample C2 84
Figure 4.9 PL spectra of Sample A2, as grown sample, (blue dotted curve),
Sample B2, irregular Au structure/SiO
2
film on the as grown sample (black
dashed curve), and Sample C2, ordered Au structure/SiO
2
film on the as grown
sample (red solid curve), all three curves normalized to the its substrate peak 85
Figure 4.10 Reflectance spectra of irregular Au nanostructure, Sample B2 (black
dashed curve) and of ordered Au nanodisk, Sample C2 (red solid curve) 88
Figure 4.11 Spectra of electric field intensity as a function of wavelengths in the
plane of irregular Au nanodisks (black dashed curve) and 100 nm above the
irregular Au nanodisks (red solid curve) for Sample B2. Inset shows the far field
projection for Sample B2 90
Figure 4.12 Spectra of electric field intensity as a function of wavelengths in the
plane of ordered Au structure (black dashed curve) and 100 nm above the ordered

Au structure (red solid curve) for Sample C2. Inset shows the far field patterns for
Sample C2 90


X

Figure 5.1 Schematic illustration of Samples A, B, and C fabrication
process 97
Figure 5.2 PL peak intensity varying with etch depths at around 940 nm from
Samples A, B, C, and D 99
Figure 5.3 PL spectra for Samples A, B, and C at etch depth of 80 nm compared
with Sample D 100
Figure 5.4a PL spectra varying with etching depth for Sample A compared with
Sample D, inset is the structure of Sample A 100
Figure 5.4b PL spectra varying with etching depth for Sample B compared with
Sample D, inset is the structure of Sample B 101
Figure 5.4c PL spectra varying with etching depth for Sample C compared with
Sample D, inset is the structure of Sample C 101
Figure 5.5 Reflectance spectrum of Sample A 105
Figure 5.6 Schematic illustration of simulated structure, Samples A, B, C, and D,
the etch depth d are 50 nm, 60 nm, 70nm, 80 nm, and 90 nm. SiO
2
thickness is 15
nm. Au thickness is 10 nm. Hole periodicity is 280 nm, radius is 70
nm 107
Figure 5.7a Simulated far field electrical intensity at 940 nm for Sample A with
different etch depth, the magnitude is represented by the color scale. The hole
etch depths in Sample A1, A2, A3, A4, and A5 are 90 nm, 80 nm, 70 nm, 60 nm
and 50 nm respectively. The schematic of structure is shown in Figure
5.6 107

Figure 5.7b Simulated far field electrical intensity at 940 nm for Sample B with
different etch depth, the magnitude is represented by the color scale. The hole
etch depths in Sample B1, B2, B3, B4, and B5 are 90 nm, 80 nm, 70 nm, 60 nm
and 50 nm respectively. The schematic of structure is shown in Figure
5.6 108
Figure 5.7c Simulated far field electrical intensity at 940 nm for Sample C with
different etch depth, the magnitude is represented by the color scale. The hole
etch depths in Sample C1, C2, C3, C4, and C5 are 90 nm, 80 nm, 70 nm, 60 nm
and 50 nm respectively. The schematic of structure is shown in Figure
5.6 108
Figure 5.7d Simulated far field electrical intensity at 940 nm for Sample D, the
magnitude is represented by the color scale. The schematic of structure is shown
in Figure 5.6 109
Figure 5.8 Simulated PL peak intensity varying with etch depth at around 940 nm
for Samples A, B, C and D 109


XI

List of Tables

Table 2.1 Concentration factors for the lowest two bands of the square lattice of
veins at the X point 41

Table 3.1 Comparison between experimental and simulation results of Ag holes
on Si with diameter of 375 nm, 340 nm, and 310 nm 50



XII


List of Publications

Journal Papers
1. Hongwei Gao, Jinghua Teng, SooJin Chua, Ning Xiang, "Enhancement of
GaAs/InGaAs Quantum Well Emission by disordered Gold Nanoparticle Arrays",
Applied physics A. In press.
2. Hongwei Gao, Kar Hoo Patrick Tung, Jinghua Teng, Soo Jin Chua, Ning
Xiang, "Coupling of surface plasmon with InGaAs/GaAs quantum well emission
by gold nanodisk arrays" Applied optics, Vol. 52, No. 16(1), June (2013).
3 .Hongwei Gao, Jinghua Teng, SooJin Chua, Ning Xiang, "Study on PL
enhancement of InGaAs/GaAs QW emission by gold nanoparticle arrays",
Journal of Molecular and Engineering Materials, submitted.
4. Hongwei Gao, Kar Hoo Patrick Tung, Jinghua Teng, SooJin Chua, Ning Xiang,
"Incorporation of SPR with Photonic Bandgap Structure to enhance
InGaAs/GaAs QW emission", to be submitted.
5. Wang Benzhong, Gao Hongwei, Lau Jun, Chua Soo Jin, "Investigation of
transmission of Au films with nanohole arrays created by nanosphere
lithography", Applied Physics A, Vol. 107 Issue 1, p139, Apr (2012).
6. K. H. P. Tung, H. W. Gao and N. Xiang, "Time evolution of self-assembled
GaAs quantum rings grown by droplet epitaxy" Journal of Crystal Growth 371
(0), 117-121 (2013).
Conference Presentations
7. Hongwei GAO, Ning XIANG, Benzhong WANG, Jinghua TENG, Soo Jin
CHUA, "Study on Light Transmission Through Silicon Covered by Ordered
Metal Particle Arrays" International Conference on Materials for Advanced
Technologies, 26
th
Jun


to 1
st
Jul 2011, Singapore.
8. Hongwei GAO, Jun Lu, Jing Hua Teng, Soo Jin Chua, Ning Xiang, "Coupling
of Surface Plasmon with Gaas/AlGaAs Quantum Well Emission by Gold
Nanoparticle Arrays", International Conference of Young Researchers on
Advanced Material, July 1
st
-6
th
, 2012, Singapore.
9. Hongwei GAO, Jinghua Teng, Soo Jin Chua, Ning Xiang, "Study on PL
enhancement of GaAs/InGaAs Quantum Well Emission by Gold Nanoparticle
Arrays",   
th
22
nd
, March,2013,SHARJAH
UNITED ARAB EMIRATES.


XIII

10. Hongwei GAO, Jinghua Teng, SooJin Chua, Ning Xiang, "Enhancement of
GaAs/InGaAs Quantum Well Emission by disordered Gold Nanoparticle Arrays",

th
 22
nd
March,2013,SHARJAHUNITED ARAB

EMIRATES.
11.Jian Huang, Hongwei GAO, Jun Lu,

Ning Xiang,

Aaron J. Danner,

Jinghua
Teng, "Photoemission Enhancement by Wavelength-Tunable Surface Plasmon
Excitation of Gold Caps on an AlGaAs Quantum Disk Array", International
Conference of Young Researchers on Advanced Material, July 1
st
-6
th
,2012,
Singapore.
12. Jian HUANG, Hongwei GAO, Kar Hoo Patrick TUNG, Aaron DANNER,
Jing Hua TENG, Ning XIANG, "Enhanced Photoluminescence by Surface
Plasmon Excitation in Gold Capped InGaAs Quantum Disk Array",7th
International Conference on Materials for Advanced Technologies, 30
th
June to 5
th

July 2013, Singapore.
13. K. H. Tung, J. Lu, H. W. GAO and N. Xiang, "Fabrication and
characterization of III-V nanostructures on ordered hexagonal through pore SiO
2

thin film", International Conference of Young Researchers on Advanced Material,

July 1
st
-6
th
, 2012, Singapore.
14. K. H. Tung, H. W. GAO, J. Lu and N. Xiang, ''Fabrication of ordered
hexagonal through pore SiO
2
thin film using porous alumina film", MRS-S, 2012.
15. Kar Hoo Patrick TUNG, Hongwei GAO, Ning XIANG,
"
Morphological and
Optical Emission Correleation of Gaas Quantum Rings Grown by Droplet
Epitaxy
"
,

7th International Conference on Materials for Advanced Technologies,
30
th
June to 5
th
July 2013, Singapore.



XIV

List of Abbreviations


EBL: Electron beam lithography

FDTD: Finite-difference time-domain

ICP: Inductively coupled plasma

LIL: Laser interference lithography

LSPR: Localized surface plasmon resonance

MBE: Molecule beam epitaxy

NSL: Nanosphere lithography

PCs: Photonic crystals

QW: Quantum well

QD: Quantum dot

SEM: Scanning electron microscopy

SPs: Surface plasmons





1


Chapter one: Introduction

1.1. General introduction of Plasmonics

Metal nanostructures had already been employed to generate beautiful colors
in glass artifacts and in windows of churches by artists before their unique optical
properties were studied. The most famous example is the Lycurgus cup which
appeared in 4th century AD. Then from the beginning of 20th century, some
scientific studies were carried out in which surface plasmons were observed.
Firstly, Robert W. Wood
1
reported unexplained features in optical reflection
measurements on metallic gratings in 1902. Later, employing the Drude theory of
metals and the electromagnetic properties of small spheres as derived by Lord
Rayleigh, Maxwell Garnett describes the bright colors observed in metal doped
glasses
2
in 1904. Later in 1908, the famous and widely used Mie theory was
developed by Gustav Mie, which described the light scattering by spherical
particles
3
. In 1956, David Pines attributed the energy losses while electrons travel
through metals to the collective oscillations of free electrons in the metal
4
, and
gave it the name  Robert Fano called the coupled oscillation of bound
electrons and light inside transparent media as 
5
in the same year. The
first theoretical description of surface plasmon was reported in 1957 with the

publication by Rufus Ritchie on electron energy losses in thin films. In this paper,
plasmon modes which can exist near the metal surface were demonstrated
6
. In
1968, the behavior of metal gratings
7
where surface plasmon resonances were
excited was described by Ritchie. In the same year, surface plasmon was optically


2

excited on metal film
8
by Andreas Otto and Erich Kretschmann, which can be
regarded as a major improvement in the study of surface plasmon. With these
methods, surface plasmons were easily generated by many researchers.
Till this time, although the properties of surface plasmon were well observed,
the relation between surface plasmon and the optical properties of metal
nanoparticles was not known yet. In 1970, the first study describing optical
properties of metallic particles
9
from the surface plasmon aspect was reported by
Uwe Kreibig and Peter Zacharias. In their report, the electronic response as well
as optical response of Au and Ag was compared. In 1974
10
, the term of surface
plasmon polariton (SPP) was introduced by Stephen Cunningham and his
colleagues. Meanwhile, strong Raman scattering from pyridine molecules which
are located close to a roughened Ag surface

11
was observed by Martin
Fleischmann and coworkers, and this opened the door for the research of Surface
Enhanced Raman Scattering (SERS).
The previous studies had built the fundamental understanding of surface
plasmon, however, there was no practical applications yet. With high density
electronics approaching the fundamental physical limits, researchers started to
seek solutions to overcome the challenge. Due to the fast-developing
nanofabrication techniques, small metallic nanostructure can be realized, which
resulted in a wide range applications
12
. Nanosized metallic structures with
promising optical properties can be integrated with electronic devices, which
significantly improve the performance of original electronic devices. According to
the records, various passive waveguides and biosensors were successfully


3

fabricated based on the unique properties of surface plasmon. Nanofabrication
techniques led to a storm of research in metal-based optics and nanophotonics,
which can be reflected in the number of scientific papers published each year.
These numbers are displayed in Figure 1.1. It is seen that the numbers almost
doubled every 5 years from 1990 onwards. This is because since 1990,
researchers could make use of commercial electromagnetic simulation codes to
design proper metallic structures; nanofabrication techniques are available to
make the desired structures, while physical analysis technique allows the analyses
of the optical properties of the metallic structures. Surface plasmon resonance
sensors were the majority among these researches, almost occupying 50% of all
publications. As time passed, besides applications in sensors, surface plasmons

were proposed to guide and manipulate light at nanometer scale, generate
extraordinary optical transmission through subwavelength metal apertures, and
perform as perfect lens
13-15
using a thin metallic film. All these applications are
reported in the articles
16,17
.


4


Figure 1.1 Number of articles varying with year
62
.

Theoretically, surface plasmons (SPs) are a kind of electromagnetic field
which exists at the interface between metal and dielectric. At this interface,
coherent electron oscillations happen when the real part of the dielectric function
changes sign across the interface. SPs can be excited by both electrons and
photons. Firing electrons into bulk metal, the electrons will be scattered. During
this process, energy can be transferred into the bulk plasma. As long as the
scattering vector has a component parallel to the surface, SPs are created.
Coupling of photons into SPs is not as straightforward. It cannot be achieved
unless a coupling medium, such as a prism or grating is used to match the wave
vector between photons from free space and wave vector of surface plasmon
propagating at the interface of metal-dielectric. There are two types of structures



5

making use of prisms to generate SPs. One is by putting a prism against a thin
metal film, which is considered as Kretschmann configuration (Figure 1.2a). The
other method is to locate the prism very close to a metal surface, as in Otto
configuration (Figure 1.2b). Besides using a prism, use of a grating is another
practical tool to compensate the incident wave vector parallel to the grating by an
amount related to its periodicity, as can be seen from Figure 1.3.

Figure 1.2 Demonstration of generating SP with prism.

Figure 1.3 Demonstration of generating SP with grating.

Besides using the prism and grating, surface plasmons can also be generated by
metallic nanoparticles with size comparable to or smaller than the incident light
wavelength. Unlike generated from a metal film, this kind of plasmon cannot
Incident
Beam
Incident
Beam
Prism
ɛ
0

Prism
ɛ
0

Metal 
1


Metal 
1

Incident
Beam




k
x

K
surface plasmon


6

propagate along the surface of metal, and is known as localized surface plasmon
(LSP). The LSP has two important effects. One is enhancing the electric field near
the particle's surface, which decreased quickly with distance from the surface. The
other is the maximum absorption of light at LSPs resonant frequency. For noble
metal nanoparticles, like silver and gold, this occurs mostly in uv-visible range.
The recent catalyst for the great interest in plasmonics

is the extraordinary
optical transmission (EOT)
18
, which was reported in 1998. Literally, EOT means

that the transmitted light is beyond the expected amount. Theoretically, it occurs
in periodic subwavelength holes milled in thin metallic films. Through this kind
of structures, the detected normalized transmission of light exceeds by orders of
magnitude more than the classical prediction made by Bethe
19
at certain
wavelength. Bethe's prediction that the transmission should depend on the
diameter of subwavelength hole d and the wavelength  with a scaling factor of

4
. To explain the origins of EOT, Ebbisen pointed out that the resonant
excitation of SPs near the surface of metal was the reason for the enhanced light
transmission. According to his explanation, the incident light first excited SPs of
periodic metallic hole structure and thus enhanced the electromagnetic field at the
metal aperture and consequently, enhanced the transmission. This point of view
has since been verified.
According to publications, both the periodicity and the size of holes have
important consequences on the plasmonic effect, which have been observed by
changing different incident angles of the excitation light for various reciprocal-
lattice directions
20,21
. The effect caused by periodicity is very obvious. As for the


7

size of holes, it was reported that both the intensity and the linewidth of
transmission peaks were increased with increase in the hole diameter
22,23
. Hole

size can also affect the location of transmission peaks. Besides the periodicity and
size of the circular holes, different shapes of hole were studied, for example the
periodic subwavelength diamond-shaped
24
hole arrays and triangles hole
arrays
25,26
. In addition, combining the shape, array symmetry and periodicity
provided a powerful tool to fabricate terahertz filters
27
. Double hole arrays with a
slight overlap between two holes generated an additional localized field
enhancement near the resulting cusps
28,29
, was reported to be used to enhance
nonlinear phenomena.
Besides EOT being caused by an array of metallic subwavelength-diameter
holes, LSP generated by metallic nanoparticles (NPs) is another interesting field.
It can confine largely enhanced electromagnetic field near the surface of NPs at
resonance wavelength, which is an important aspect of LSPs. The term
'localization' means that the high spatial resolution (subwavelength), is only
limited by the size of NPs. These promising properties make LSP popular for
various applications. For instance, strong EM fields can be employed in
enhancing spectral information for surface-enhanced Raman spectroscopy (SERS),
metal-enhanced fluorescence (MEF), plasmon resonance energy transfer
(PRET)
28,30
, and nanoplasmonic molecular rulers
31,32
. Importantly, the largely

enhanced electromagnetic field only exists around LSP resonance wavelength.
Thus, in order to utilize the strong electromagnetic field near the surface of NPs
effectively, tuning LSP resonance to the desired wavelength becomes crucial.


8

Researchers have devoted great effort to achieve this goal. It is reported that the
LSP resonance wavelength can be adjusted by varying the type of material and
surrounding medium, size or shape of metallic NPs, and the arrangement of
metallic nanostructures.
Among these wide research fields related to LSPs, we review only the
plasmonic effect on the photoluminescence (PL) from solid-state light emitting
materials, including InGaN/GaN quantum well, organic light emitting diodes,
CdSe quantum dots, and Si photonics.
By coating a metal layer on InGaN/GaN material, large photoluminescence
(PL) enhancement was reported by Koichi Okamoto
33
. They grew InGaN/GaN
single QW (3 nm) structures on sapphire substrates with metal organic chemical
vapor deposition (MOCVD) technique. After the growth of single QW, metal was
deposited on it. Three metals were used. They were silver, aluminum, and gold.
The thickness of each metal was chosen to be 50 nm. The sample structure is
shown in Figure 1.4a. The QWs were excited from the bottom, using a 406 nm
cw-InGaN diode laser. The PL signals were also collected from the substrate side.
PL emission spectrum of each sample is plotted in Figure 1.4b. Comparing PL
peak intensity from Ag-coated sample with that from an uncoated sample, a 14-
fold enhancement was observed around 470 nm. The enhancement factor is as
high as 17 fold for the integrated PL intensity. However, there was no
enhancement caused by Au coating. As for the Al-coated sample, the peak

intensity is enhanced by a factor of 8 while the integrated intensity is enhanced by
a factor of 6. The authors explained their experimental results using the coupling


9

effect between SPs and QW emission. The excited SPs intensified the
electromagnetic field near the QW located close to the metal film, which
increased the density of state as well as the spontaneous emission rate of QW.
This effect resulted in the enhancement of light emission. As the SPs resonance of
Au occurred at a longer wavelength than the QW emission wavelength (470 nm),
no PL enhancement was obtained from samples coated with Au.


Figure 1.4 (a) Sample structure of InGaN/GaN QW and excitation/emission of PL
measurement. (b) PL spectra of InGaN/GaN QWs coated with Ag,Al, and Au. The PL peak
intensity of uncoated InGaN/GaN QW at 470 nm was normalized to 1
33
.

The PL enhancement varying with wavelength with a spacer layer of 10 nm
between metal layer and QWs, is shown in Figure 1.5a. At shorter wavelengths,
the enhancement ratio from Ag sample was increased. As for Al samples, the
enhancement ratio was almost constant, independent of wavelength. PL intensities
varying with the distance between QWs and metal layers is shown as Figure 1.5b.
The spacer thickness of 10 nm, 40 nm and 150 nm was used between QW emitter
and metal coating. PL intensity from Al and Ag samples was found to decrease


10


exponentially with the increase in spacer thickness, but there is no such behavior
for Au-coated QWs as shown in Figure 1.5a.


Figure 1.5 (a) PL enhancement ratios at several wavelengths for the same sample as in
Figure 1.4(b). (Inset) Dispersion diagrams of surface plasmons generated on Ag/GaN,
Al/GaN, and Au/GaN surfaces. (b) Integrated PL enhancement ratios for samples with Ag,
Al, and Au are plotted against the thickness of GaN spacers. The solid lines are the
calculated values by the penetration depths
33
.

11-fold enhancement of light emission from organic thin films using SP-
OLED
34
coupling was reported by Neal. T. D Half of substrate was metalized
with either Ag or Au. Then the substrates were coated with a dye layer to a
thickness of ~ 200 nm. The dye used was Coumarin 460. With a half metalized
substrate and half bare substrate, a fast and direct comparison can be observed
between polymer emission on top of Au/Ag layer and the polymer emission on
the bare quartz substrate. The sample structure and PL spectra are shown in
Figures 1.6a and 1.6b respectively. It is seen that an 11-fold PL intensity
enhancement is obtained from the dye layer on Ag film, compared to that on a
bare quartz substrate. This is attributed to the coupling effect of SPs generated by
Ag with the dye emission. Since the SPs resonance wavelength from Ag film is