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Structural Characterization of Gallium Antimonide Semiconductor Used in Air Space Station

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Structural Characterization of Gallium Antimonide Semiconductor Used in Air Space Station Structural Characterization of Gallium Antimonide Semiconductor used in Air Space Station. By BAMBA MAHMAN RESEARCH DISSERTATION Submitted in fulfillment of the requirements for the degree of MASTER OF SCIENCE in PHYSICS in the FACULTY OF HEALTH SCIENCES (School of Pathology and Preclinical Sciences) at the SEFAKO MAKGATHO HEALTH SCIENCES UNIVERSITY Supervisor: Mrs M.R. Mhlongo Co-Supervisor: Dr M.E. Sithole 2015 i ACKNOWLEDGEMENTS I would like to thank the following people: My supervisor, Mrs MR Mhlongo for her support and supervision throughout the study. My co-supervisor Dr ME Sithole for his support and help throughout the study. Dr C Baker for assisting with the measurement of data required for my studies. My sincere thanks to some of the staff and students in Physics Department for their support. Finally I would like to thank my wife and children for being supportive to my studies. ii TABLE OF CONTENTS Pages Declaration i Acknowledgements ii Table of Contents iii List of Symbols and abbreviations vi Abstract 1 Chapter 1: Introduction 2 1.1 Background 2 1.2 Objectives 5 1.3 Outline of this book 5 1.4 References 5 Chapter 2: Literature Review 6 2.1 Introduction 6 2.2 Review 6 2.3 References 16 Chapter 3: Semiconductor Material 23 3.1 Introduction 23 3.2 Valence and conduction bands 23 3.3 Intrinsic semiconductor 26 3.4 Extrinsic semiconductor 26 3.5 Energy band structure 27 3.5.1 The Fermi level 28 3.5.2 Shallow and deep states 29 3.5.3 Impurities and defects 29 3.6 General properties of GaSb 30 3.7 Growth techniques 32 3.7.1 Bulk crystal growth technique 32 3.7.2 Epitaxial growth techniques 33 3.8 Application of GaSb 34 3.9 References 35 iii Chapter 4: Scanning Electron Microscopy System 37 4.1 Introduction 37 4.2 Major component 38 4.2.1 Electron gun 39 4.2.2 Electron beam 42 4.2.3 Electron probe 43 4.2.4 Detectors 44 4.3 Sample Holder 46 4.4 Topography 47 4.5 Physical Operation 49 4.6 References 49 Chapter 5: Methodology 51 5.1 Introduction 51 5.2 Sample 51 5.3 Experimental procedure 52 5.4 Cleaning Procedure 52 5.5 Etching Process 53 5.6 Annealing Process 54 5.7 Electron Irradiation Process 55 5.8 Oxygen Sputtering Process 56 5.9 Argon Sputtering Process 57 5.10 Image Requisition 58 5.10.1 Set up of the system. 58 5.10.2 Sample Preparation 59 5.10.3 Loading the Sample 59 5.10.4 Sample Scanning 60 5.11 References 60 iv Chapter 6: Results and Discussion 62 6.1 Introduction 62 6.2 Control sample 62 6.3 Experimental samples 63 6.3.1 Annealing 63 6.3.2 Chemical etching 65 6.3.3 Argon sputtering 68 6.3.4 Oxygen gas 70 6.3.5 Electron bombardment 71 6.4 References 73 Chapter 7: Conclusion 74 7.1 Introduction 74 7.2 Chemical etching 74 7.3 Annealing process 74 7.4 Argon sputtering 75 7.5 Oxygen gas 75 7.6 Electron bombardment 75 7.7 Conclusion 75 7.8 Recommendation 76 7.9 References 76 Appendices 77 Appendix A: List of tables 77 Appendix B: List of figures 77 v LIST OF SYMBOLS AND ABBREVIATIONS AFM Atomic Force Microscope CMOS Complementary Metal-Oxide Semiconductor CRT Cathode Ray Tube DLTS Deep level transient spectroscopy DOS Density of State EBSD Electron Backscattered Diffraction EDAX Energy Dispersive Analysis X-ray (Technique) EDS Energy Dispersive Spectroscopy E Eutectic E + M Etching system modified by adding 10% Magnesium oxide to increase its viscosity EL2 Energy level 2 EPD Epitaxial Density FEGSEM Field Emission Gun Scanning Electron Microscopy EF Fermi level FWHM Full Width at Half Maximum HB Horizontal Bridgman HCI Highly charged ions HDTV High Definition TV HEMT High-Electron-Mobility Transistors IC Integrated Circuit LEC Liquid Encapsulated Czochralski ISS International Space Station LEED Low Energy Electron Diffraction LPE Liquid Phase Epitaxy LVSEM Low Voltage SEM MBE Molecular Beam Epitaxy MCA Multichannel Analyser MESFET Metal-Semiconductor Field Effect Transistors MISSE Materials International Space Station Experiment MOCVD Metal Organic Chemical Vapour Deposition vi MOVPE Metal Organic Vapour Phase Epitaxy NASA National Aeronautic and Space Administration NIXSW Normal Incidence X-ray Standing Wave SEM Scanning Electron Microscope SEXAFS Surface Extended X-ray Absorption Fine Structure STEM Scanning Transmission Electron Microscope SOS Silicon On Sapphire STM Scanning Tunneling Microscope SWBXT Synchrotron White Beam X-ray Topography SXRD Surface X-ray Diffraction TEM Transmission Electron Microscope UHV Ultra-High Vacuum VPE Vapour-Phase Epitaxy WDS Wavelength Dispersive Spectroscopy XANES X-ray Absorption Near-Edge-Structure Spectroscopy XSW X-ray Standing Wave vii ABSTRACT This experimental study followed the following procedure; cutting of GaSb material into samples, cleaning of samples, exposing them to various treatment conditions and analysing their surface morphologies. The n-type GaSb wafer with orientation (100) was used. Some samples were exposed to a concentration of HCl for chemical etching for different time settings, annealed, exposed to oxygen and argon fluxes and irradiated with different electron fluxes. The scanning electron microscope (SEM) was used to determine the morphological information and orientation of the samples. The samples’ maps and images were plotted and reported for each treatment condition and compared. Bombarding the sample surface with different electrons fluxes, increased the atom mobility throughout the surface. The samples exposed to various temperatures exhibited rough surface with an increasing roughness as the temperature was increased. The etching treatment time has shown some effects on the morphology of GaSb semiconductor material. Bombarding GaSb semiconductor samples with both oxygen and argon gasses showed an increase in the size of the holes as the fluency increases. The study has shown that an increase in particle dose caused damage or introduced defects on the surface of GaSb semiconductor material. The study recommends that the semiconductor material be treated before been used under certain conditions to improve the favorable conditions for devices on the material. Keyword: Gallium Antomonide, Semiconductor material, Treatment Conditions, Scanning Electron Microscopy 1 CHAPTER 1 INTRODUCTION 1.1 BACKGROUND Semiconductors are materials used in a variety of technologies on which human beings depend. Such technologies include laser diodes used in TV transmission, high definition TV (HDTV) development, medical and military applications. They are also used in thermoelectric coolers based on the Peltier effect to maintain a constant temperature in satellite communication and in solar panels to convert light to electricity etc… However, the harsh conditions to which they are exposed negatively affect their morphology, microstructure, electrical and electronics properties. To solve those problems chips manufacturers have turned to radiation hardening techniques by manufacturing hardened chips on insulating substrates such as SiO2 and silicon on sapphire (SOS). However, air particles like N2, O2, H2O, CO2 etc can have negative impact on semiconductor structures in general and on SiO2 in particular. For example, it is reported by Winokur (2000), that one of the popular candidates for space applications is the complementary metal-oxide semiconductor (CMOS) technology due to its low power and voltage requirements. The most likely failure mechanism for CMOS resulting from total ionization dose is the loss of isolation caused by parasitic leakage paths between the source and the drain of the device (Adams 1982). However, total ionization hardness can be achieved by making changes in the isolation structure. One of the changes is to form a heavily doped region by ion implantation that effectively shuts off radiation-induced parasitic leakage paths. In addition to that, products based on semiconductor technology are still 2 expensive, for example solar panels that are very important source of clean energy, are not affordable. Gallium antimonide (GaSb) semiconductor material has received increasing attention because its wavelength covers a wide range of applications which go from 1.24 µm to 4.3 µm. It has turned out to be a promising material for the application in long wavelength lasers and photodectors for fibre optical communication system. http://www.hindawi.com/journals/amse/2010/923409/ The semiconductor materials used in air space stations are regularly exposed to radiation particles. Cosmic rays that come from all directions are believed to be consisting of approximately 85% of protons, 14% of alpha particles, and 1% of heavy ions together with x- rays and gamma-rays radiation with energies between 108 and 1010 eV (https://en.wikipedia.org/wiki/Radiation_hardening). This is a concern for spacecraft and high altitude aircraft. These particles cause lattice displacement by changing the arrangement of the atoms in the crystal lattice, creating lasting damage, and increasing the number of recombination centers and worsening the analog properties of the affected semiconductor junction. The charged particles also cause ionization effects which are usually transient, creating glitches and soft errors that can lead to destruction of the device if they trigger other damage mechanism such as photocurrent caused by ultraviolet and x-ray radiation. Materials International Space Station Experiment (MISSE) has attached seven different experiments outside the International Space Station (ISS) to evaluate the effects of atomic oxygen, vacuum, solar radiation, micrometeorites, direct sunlight and extreme heat and cold. The results of these experiments were expected to provide a better understanding of the 3 durability of various materials when exposed to such an extreme environment. It is believed that many of the materials may have applications in the design of future spacecraft. (https://www.google.co.za/?gfe_rd=cr&ei=32SqVs-bD-yo8we8- Y2ACg&gws_rd=ssl#q=material+international+space+station+experiment+(misse)) Therefore more research needs to be done to improve the performance, the quality and the duration of those products and also to reduce their costs The purpose of this study was to analyse the surface morphology of GaSb semiconductor material after being exposed to various treatment conditions.
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