GaN-on-Si(100) NANOSTRUCTURES FOR OPTOELECTRONICS APPLICATIONS ANSAH-ANTWI KWADWO KONADU NATIONAL UNIVERSITY OF SINGAPORE 2015 GaN-on-Si(100) NANOSTRUCTURES FOR OPTOELECTRONICS APPLICATIONS ANSAH-ANTWI KWADWO KONADU (B.Eng.(1st Hons.), University of Ghana) A THESIS SUBMITTED FOR THE DEGREE OF DOCTORATE IN PHILOSOPY DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE 2015 ! ii! DECLARATION I hereby declare that the thesis is my original work and it has been written in its entity 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 Ansah-Antwi Kwadwo Konadu 20 January 2015 ! iii! Acknowledgements ! May I take this opportunity to express my appreciation to my Heavenly Father who has kept me alive and made every provision possible for me throughout all these years I am indeed grateful to the Agency of A*STAR Graduate Academy (A*GA) for the PhD fellowship To all the staff of the A*GA secretariat I wish to extend a warm and hearty appreciation for your support in various capacities To the best supervisor in the world in the person of Prof Chua Soo Jin of the Department of Electrical and Computer Engineering, NUS, I wish to say a big thank you for all the years of nurturing and mentoring To me you were more than an advisor or mentor, your experience with handling students of different cultures cannot go unnoticed Sometimes in life, we meet people who are simply nothing more than God-sent, and this is what you have been to me To Dr Soh Chew Beng of Singapore Institute of Technology, you continued to be of immense support even after seized being my official co-supervisor My heart goes out to you for always stepping out and going the extra miles to see to it that I was comfortable and making progress with my research work To Dr Liu Hongfei, my diligent co-supervisor, you were indeed the most inspirational person that I might have encountered in the field of research I have benefited immeasurably from your keen sense of analytical reasoning To all my colleagues in the Centre for Optoelectronics laboratory especially Ian Seetoh, Jian Wei, Zhang Li, Tang Jie, Liu Yi and Chengguo, your companionship and cooperation meant a lot to me and I will always remember the good lunch and Chinese New Year celebrations we had at Prof Chua’s residence My sincere appreciation also goes to Dr Yang Ping and Dr Sascha Heussler of Singapore Synchrotron Light Source (SSLS) And lastly to the staff of the Institute of Materials Research and Engineering who made my stay worthwhile both professionally and socially, especially Eric Xiaosong, Vincent Lim, Neo Kiam, David Paramella, Jarrett Dummond and Hannah Lim, I salute all of you Most of all, I will like to thank my beloved family and loves who have been with me through both the happy and sad moments I appreciate all your prayers and encouragement ! iv! Table of Contents Acknowledgements iv Summary ix List of Figures xi List of Tables xxviii CHAPTER ONE: Introduction 1 Summary 1.1 Properties of AlN, InN and GaN materials 1.1.1 Crystal structure of III nitride semiconductors 1.1.2 Electronic and Optical properties of III-nitrides 1.2 Si as a semiconducting material 1.2.1 Physical properties of Si 1.2.2 Pitfalls of Si as a material for optoelectronics 1.3 The battle for the optoelectronic space 11 1.3.1 Integration of GaN and silicon 11 1.4 Objectives 13 1.5 Motivation 14 1.6 Scope of thesis 15 CHAPTER TWO: Overview of research work on GaN-on-Si(100) 17 2.1 Introduction 17 2.1.1 Bulk GaN substrate developments 19 2.1.2 Ga-melt based bulk GaN 19 2.1.3 Na flux method 20 2.1.4 Hydride Vapor Phase Epitaxy (HVPE) 22 2.1.5 Ammonothermal method 23 ! v! 2.2 Heteroepitaxy of GaN-on-Si 25 2.3 Challenges with the heteroepitaxy of GaN-on-Si 27 2.3.1 Lattice mismatch and surface atomic symmetry 27 2.3.2 Coefficient of thermal expansion mismatch 31 2.3.3 Lack of semi-insulating Si substrates 33 2.3.4 Diffusion of Si into GaN thin film 34 2.3.5 Absorption of light emitted from the InGaN/GaN active layer by the Si substrate 36 2.4 Approaches to solve the challenges of the growth of GaN on Si 36 2.4.1 Buffer layer technology 37 2.4.2 Use of Miscut substrate for the growth of high quality GaN epilayer 39 2.4.3 Transfer of GaN based devices unto a pseudo/virtual-substrate 43 2.4.4 Growth of GaN epilayer on patterned foreign substrates 44 2.4.5 Growth of GaN on {111} sidewall of Si(100) substrate 46 2.5 Non-polar and Semi-polar GaN 52 CHAPTER THREE: Equipment and Materials 54 Introduction 54 3.1 UV Mask aligner 54 3.2 Reactive Ion Etching System (RIE) 55 3.3 Plasma enhanced chemical vapor deposition (PECVD) 57 3.4 Metalorganic chemical vapor deposition (MOCVD) 58 3.5 X-ray diffraction (XRD) 65 3.6 Scanning electron micrograph 67 3.7 Transmission electron microscope 68 3.8 Atomic force microscope (AFM) 69 3.9 Raman scattering and Photoluminescence spectroscopy 70 ! vi! CHAPTER FOUR: Effect of substrate patterning/modification on the quality of GaN epilayer grown on Si(100) substrate by MOCVD 72 4.1 Summary 72 4.1.1 Introduction 72 4.1.2 Surface patterning of Si(100) substrate by UV lithography 74 4.1.3 Anisotropic etching of Si(100) substrate in an aqueous potassium hydroxide (KOH) solution 76 4.2 MOCVD heteroepitaxial growth process of III-nitride films 80 4.2.1 Surface morphology of the as-grown GaN layer 83 4.2.2 Crystal structure characterization of as-grown GaN epilayer grown on {111} facets exposed on Si(100) substrate 90 4.2.3 Optical characterization of as-grown GaN epilayer grown on the {111} facets exposed on Si(100) substrate 96 4.3 Surface passivation of the Si(100) substrate with dielectric films 114 4.4 Increased GaN growth selectivity with Titanium nitride (TiN) film as passivation layer 115 4.4 Conclusions 118 CHAPTER FIVE: Crystallographically Tilted and Partially Strain Relaxed GaN Grown on Inclined {111} Facets etched on Si(100) Substrate 121 5.1 Summary 121 5.1.1 Introduction 122 5.1.2 Template preparation and patterning fabrication 122 5.1.3 Surface analysis of the Si{111} facet exposed on the Si(100) substrate 125 5.1.4 MOCVD Growth of III-nitride films on patterned Si(100) and conventional Si(111) substrates 127 ! vii! 5.2 Evidence of the crystallographic tilt by reciprocal space mapping (RSM) and HRXRD study of as-grown GaN film 132 5.3 Optical property evaluation by µ-PL and µ-Raman spectroscopy 137 5.4 Dislocation bending away from the GaN(10-11) plane 143 5.5 Conclusions 146 CHAPTER SIX: Surface step assisted threading dislocation density reduction in GaN epilayer grown on V-grooved on-axis Si(100) substrate 148 Summary 148 6.1 Introduction 149 6.1.1 Template fabrication and materials’ growth 151 6.1.2 Surface morphology of etched Si(100) surface 155 6.1.3 HRXRD study of the crystal quality and extended defect density of GaN epilayer 158 6.1.4 Evaluation of optical quality of as-grown GaN epilayer by PL spectroscopy and Raman scattering 162 6.2 Determination of relationship epitaxial tilt and substrate offset 166 6.2.1 Vicinal surface assisted dislocation reduction mechanism in GaN epilayer 168 6.3 Facet controlled III-nitride epilayer grown on an inclined Si{111} plane 173 6.4 Conclusions 182 CHAPTER SEVEN: Conclusions and Future Perspective 184 7.0 Conclusions 184 7.1 Future Perspective 189 Bibliography 191 Publications 209 Conference Presentations 211 Awards for thesis work 213 ! viii! Summary In this thesis, approaches to grow high quality GaN-based nanostructures on Si(100) substrate were developed Due to the large coefficient of thermal expansion (CTE) mismatch of 56% between the Si substrate and the GaN layer, the use of surface-patterned/modified Si substrates help to reduce the cracking of the as-grown GaN epilayer The III-nitride [Ga(Al, In)N) films were deposited on the Si(111) sidewalls that were exposed on the Si(100) substrate after potassium hydroxide (KOH) anisotropic etching Triangle/hexagon array of the anisotropically exposed Si(111) facets sidewalled holes was found to be critical to obtain coalescence of the GaN epilayer after it had overgrown above the etched holes In another experiment, the quality of the GaN epilayer grown on the exposed Si(111) facets of the V-shaped trenches on the Si(100) substrate was contrasted with the GaN epilayer grown on the planar Si(111) substrate Higher surface quality of the exposed Si(111) facets were obtained for cases where the trenches were aligned either perpendicularly or parallely to the Si[011] crystallographic direction Vicinal surface induced steps on the exposed Si(111) facets resulted in crystallographic tilt between the (0002) plane of the III-nitride epilayers and the Si(111) plane This crystallographic tilt was found to be related to the improvement of the crystal quality and the enhancement of about times higher internal quantum efficiency (IQE) of the GaN epilayer grown on the exposed Si(111) sidewalls of the V-groove trenches compared to the GaN epilayer grown on the planar Si(111) substrate ! ix! To further study the effects of surface steps on the properties of the as-grown GaN epilayer, the height of the steps was engineered by misaligning the µm wide trenches at predetermined angles α, (i.e 2, and 6o) away from the Si[011] crystallographic direction The misaligned trenches exhibited steps with different heights on the exposed Si(111) facets after anisotropic etching in KOH solution 50 nm thick AlN buffer layer was deposited on the slanted Si(111) facet with AlGaN as an interlayer The growth structure was terminated with 500 nm – µm thick GaN epilayer It was found that GaN epilayer grown on the V-grooves aligned at 6° away from the Si[011] direction had the lowest threading dislocations (TDs) density of about 2.1 x 108 cm-2 which was about two order of magnitude lower than the TDD in other GaN samples with different misalignment angles The reduction in the TDs was achieved through the bending of the dislocations away from the GaN epilayer by the 3D islands of the AlN buffer layer From the above observation, GaN/InGaN(10-11) rod with a triangular cross section was grown lying on a single Si(111) sidewall of the etched V-groove The other Si(111) sidewall was completely isolated from the GaN deposition The deposition of the GaN/InGaN triangular rod on the single sidewall of the V-grooves was achieved by aligning the trench’s longitudinal axis perpendicularly to the flow direction of the precursor gas within the boundary layer over the substrate This method promises to be cheaper and a reproducible route to prepare GaN epilayer on the single facet of the V-groove trench [for a turbo disk MOCVD system] with crystal quality compared to the conventional method via surface passivation ! 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Publications "Crystallographically tilted and partially strain relaxed GaN grown on inclined {111} facets etched on Si(100) substrate", K K Ansah Antwi, et al., J Appl Phys 114 243512 (2013) “Growth optimization and characterization of GaN epilayer grown on multifaceted {111} surface exposed on Si(100) substrate”, K K Ansah-Antwi, Hongfei Liu, Chew Beng Soh and Chua Soo Jin, under revision, Journal of Vacuum Science and Technology A “Surface-steps-assisted threading dislocation density reduction in GaN epilayer grown on on-axis V-grooved Si(100) substrate”, K K Ansah-Antwi, et al., in review., Crytal research and Technology “Spatial control of (10-11)GaN rod lying on a single {111} sidewall of V-grooved Si(100) substrate”, K K Ansah-Antwi, Hongfei Liu, Shiju Li and Chua Soo Jin, to be submitted “Aqueous Chloride Ion detection with nano and micro-ridged InN gated InGaN/GaN transistor”, Soh Chew, K K Ansah-Antwi et al, in review, Journal of Applied Physics D “Electron-beam-induced carbon deposition on high-indium-content AlInN thin films grown on Si substrates at elevated temperature”, H F Liu, C G Li, K K Ansah Antwi, et al., Materials Lett 128, 344-348 "Multi-scale Ommatidial Arrays with Broadband and Omnidirectional Anti-reflection and Anti-fogging Properties by Sacrificial Layer Mediated Nanoimprinting”, Hemant Kumar Raut, Saman Safari Dinachali, Loke Yee Chong, K K Ansah-Antwi et al., ACS Nano, 2015, (2), pp 1305–1314 ! 209! Atomic layer deposition of crystalline Bi2O3 thin films and their conversion into Bi2S3 by thermal vapor sulfurization, Hongfei Liu, K K Ansah-Antwi et al., RSC Advances, 2014, DOI: 10.1039/C4RA09896J “Towards large-area and continuous MoS2 atomic layers grown via vapor-phase growth: thermal vapor sulfurization”, Hongfei Liu, K K Ansah-Antwi, et al., Nanotechnology, 25 405702 (2014) 10 "Epitaxial synthesis, band offset, and photoelectrochemical properties of cubic Ga2S3 thin films on GaAs (111) substrates" Hongfei Liu, K K Ansah-Antwi, Chin Sheng Chua, Jian Huang, Soojin Chua, and Dong Zhi Chi, ECS Solid State let 2014 3(11): P131-P135; doi:10.11492/2.0021411 ssl 11 “Synthesis and Phase Evolutions in Layered Structure of Ga2S3 Semiconductor Thin Films on Epiready GaAs (111) Substrates” Liu, Hongfei, K K Ansah-Antwi et al., ACS Appl Mater Interfaces, Article ASAP, DOI: 10.1021/am4056535 12 “Nanopore morphology in porous GaN template and its effect on the LEDs emission”, C B Soh, C B Tay, Rayson J N Tan, A P Vajpeyi, I P Seetoh, K K Ansah-Antwi and S J Chua, J Phys D: Appl Phys (2013) 46 365102 13 “Vapor-phase growth and characterization of Mo1−xWxS2 (0 ≤ x ≤ 1) atomic layers on 2-inch sapphire substrates”, Hongfei Liu, K K Ansah-Antwi et al., Nanoscale (2013) 6, 624-629: Top 10 most read article, Q1-2014 ! 210! 14 “Fabrication of highly uniform and porous MgF2 anti-reflective coatings by polymer-based sol–gel processing on large-area glass substrates”, Hemant Kumar Raut, Saman Safari Dinachali, K K Ansah-Antwi, et al., Nanotechnology (2013), 24 505201 15 “Large Area, Facile Oxide Nanofabrication via Step-and-Flash Imprint Lithography of Metal–Organic Hybrid Resins”, Saman Safari Dinachali, Jarrett Dumond, Mohammad S M Saifullah, K K AnsahAntwi et al., ACS Appl Mater Interfaces, (2013) (24) 13113-13123 Conference Presentations “A facile method for reducing threading dislocation density in GaN epilayers via vicinal surfaces”, K K Ansah-Antwi et al., 2014 MRS Fall Meeting & Exhibit, Boston, USA, November 30-Dec 2014 “MOCVD of GaN-on-Si(100): Template Design and its Effects on GaN growth/properties”, K K Ansah-Antwi et al., 4th M3 Conference, Biopolis, Singapore, January 14-16, 2014 “Strain relaxation Mechanism of GaN epilayer grown on spatially exposed Si(111) surface on Si(100) substrate”, K K Ansah-Antwi et al.,6th Asia Pacific Workshop on Widegap Semiconductors, TamsuiNew Taipei City, Taiwan, May 2013 “Nitrogen implanted micropatterned sapphire for growth of partially strain- relaxed GaN with lower edge dislocation density” C B Soh, L H Chua, Q X Wee, H R Tan, Rayson J N Tan, K K Ansah- ! 211! Antwi and S J Chua, 6th Asia Pacific Workshop on Widegap Semiconductors, Tamsui-New Taipei City, Taiwan, May 2013 ”Effect of KOH solution temperature on the quality of GaN grown on patterned Si(100) substrate”, K K Ansah-Antwi et al., International Conference on Nitrides (IWN 2012), Sapporo, Japan, October 2012 “Green-Photonics LEDs with novel III-Nitride quantum dots for red emission”, C B Soh, K K Ansah-Antwi et al., International Conference on Nitrides (IWN 2012), Sapporo, Japan, October 2012 “Site controlled microporous Si substrate for growth of high quality strain relaxed GaN/InGaN MQWs”, K K Ansah-Antwi, et al., International Conference of Young Researchers on Advance Materials (ICYRAM), Singapore, July 2012 ! 212! Awards for thesis work Best Poster Award, IMRE Scientific Research Forum (ISRF), 2nd and 3rd October 2014, Singapore Best Poster Award (Co-author), 4th Trilateral Conference on Advances in Nano Science: Energy, Water and Healthcare, 5-7 December 2013, Singapore Best Poster Award (2nd Place), IMRE Postgraduate Poster Competition, 2013, Singapore Best Poster Presentation (1st Place), 3rd NUS ECE Graduate Student Symposium 2013, Singapore Best Paper Presentation (3rd Place), 3rd NUS ECE Graduate Student Symposium, 2013, Singapore Best Poster Award (3rd place), IMRE Postgraduate Poster Competition, 2011, Singapore ! 213! .. .GaN- on- Si(100) NANOSTRUCTURES FOR OPTOELECTRONICS APPLICATIONS ANSAH-ANTWI KWADWO KONADU (B.Eng.(1st Hons.), University of Ghana) A THESIS SUBMITTED FOR THE DEGREE OF DOCTORATE... characterization of as-grown GaN epilayer grown on {111} facets exposed on Si(100) substrate 90 4.2.3 Optical characterization of as-grown GaN epilayer grown on the {111} facets exposed on Si(100). .. electrons of Al to the nucleus, a strong attraction force between the protons of the nucleus and the valence electrons is responsible for the small lattice constant and the large bandgap With GaN