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 I 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 Xiang 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 II 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 General introduction of Plasmonics 1 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 III 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 IV 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 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 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 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 V 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 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 7.6fold enhancement in the photoluminescence intensity has been obtained All the experimental results were verified by numerical simulations VI List of Figures Figure 1.1Number of articles varying with year Figure 1.2 Demonstration of generating SP with prism Figure 1.3 Demonstration of generating SP with grating 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 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 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 media and excitation/emission configuration of PL measurement (b) PL spectra of Si/SiO 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: ɛ1 =2.33 (SiO ), ɛ2 =17.88 (InSb) 38 VII Figure 2.6 The photonic band structure for the lowest- frequency modes of a square array of dielectric (ɛ=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 (ɛ=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 (ɛ=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 o f 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 VIII 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 circleshape 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 /Au nanodisk arrays, Sample A1 (solid curve) 76 Figure 4.4 Reflectance spectrum of Sample A1: Au nanodisk arrays on SiO 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 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 film on the as grown sample (black dashed curve), and Sample C2, ordered Au structure/SiO 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 IX To match a longer QW emission wavelength and simplify the fabrication process, some irregularity was introduced to the Au nanodisk arrays on top of thin SiO2 film which is attached on the InGaAs/GaAs QW system Because of the irregularity, the number of mixing SP modes was increased, and the exit angle of LSP bright modes was enlarged, which means that the light being coupled to the outside of the chip was increased By fabricating irregular Au nanodisk arrays/SiO on top of InGaAs/GaAs QW system, more than 2- fold enhancement of PL intensity has been obtained A thin barrier layer (