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Ch.1 Introduction

Ch.1 Introduction. Optoelectronic devices : - devices deal with interaction of electronic and optical processes Solid-state physics : - study of solids, through methods such as quantum mechanics, crystallography, electromagnetism and metallurgy Elemental semiconductors :

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Ch.1 Introduction

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  1. Ch.1 Introduction • Optoelectronic devices: • - devices deal with interaction of electronic and optical processes • Solid-state physics: • - study of solids, through methods such as quantum mechanics, crystallography, electromagnetism and metallurgy • Elemental semiconductors: • - Si, Ge, ..etc. • - indirect bandgap, low electric-optics conversion efficiency • Compound semiconductors • -III-V (e.g. GaN, GaAs), II-VI • -direct bandgap, high electric-optics conversion efficiency • GaAs, InP • - higher mobility than Si, Ge, • - energy band gap, Eg: 1.43 (GaAs), 1.35 (InP) • - most common substrate, used to grow up compound semiconductors

  2. Periodic Table

  3. Band structure • Band structure: • - results of crystal potential that originates from equilibrium arrangement of atoms • in lattice - directed from potential model and electron wave equation (Schrodinger equation) time-dependent Schrodinger equation E: electron energy, φ:wave equation, m: electron mass, ħ: Plank constant

  4. Electron energy band diagram v.s. wave number

  5. Energy bandgap v.s. lattice constant

  6. Bonding in solids • Van der Waals bonding: formation of dipoles between atoms and their electrons e.g.: inert gas, like Ar • Ionic bonding: electron exchange between atoms produces positive and negative ions which attract each other by Coulomb-type interactions e.g. NaCl, KCl • covalent bonding sharing of electrons between neighboring atoms e.g.: elemental and compound semiconductors • Metallic bonding: valence electrons are shared by many atoms (bonding not directional, electron free or nearly free contributed to conductivity) e.g.: Zn

  7. Body-Centered Cubic (BCC) structure http://stokes.byu.edu/bcc.htm e.g. iron, chromium, tungsten, niobium

  8. Face-Centered Cubic (FCC) structure e.g.: aluminum, copper, gold, silver http://stokes.byu.edu/fcc.htm

  9. Diamond Cubic (FCC) structure http://zh.wikipedia.org/zh-tw/File:Diamond_Cubic-F_lattice_animation.gif

  10. Zincblende structure • Diamond structure, Zincblende structure e.g.: Si, Ge e.g.: aluminum, GaAs

  11. Atomic arrangement in different solids

  12. Dislocation & strain • Dislocationoccurs if - epitaxial layer thickness > hc (critical thickness), or - epitaxial layer thickness < hc, but with large mismatch • Strain occurs if - epitaxial layer thickness < hc, and with small mismatch

  13. Strain semiconductor • a) lattice match b) compressive strain c) tensile strain • Strain offer flexibility for restriction of lattice mismatch

  14. Crystal Growth • Bulk growth: - furnace growth - pulling technique • Epitaxial growth: - Liquid Phase Epitaxy (LPE) - Vapor Phase Epitaxy (VPE), or termed Chemical Vapor Deposition (CVD) - Molecular Beam Epitaxy (MBE)

  15. Epitaxy • epi means “above” taxis means “in order manner” epitaxy can be translated to “to arrange upon” • with controlled thickness and doping • subtract acts as a seed crystal, deposited film takes on a lattice structure and orientation identical to the subtract • different from thin film deposition that deposit polycrystalline or amorphous film • - homoepitaxy: epi and subtract are with the same material • epi layer more pure than subtract and have different doping level - hetroepitaxy: • used for - Si-based process for BJT and CMOS, or - compound semiconductors, such as GaAs

  16. Epitaxy Material Growth Methods • Liquid Phase Epitaxy • Vapor Phase Epitaxy (VPE), or termed Chemical Vapor Deposition (CVD) - formation of condensed phase from gas of different chemical composition - distinct from physical vapor deposition (PVD) such as sputtering, e-beam deposition, MBE (condensation occurs without chemical change) - gas stream through a reactor and interact on a heated subtract to grow epi layer • Molecular Beam Epitaxy

  17. Doping of Semiconductors • Intrinsic materials:undoped • - Undoped materials by epitaxy technology have more carriers than in intrinsic • material. e.g. GaAs: 1013 /cm3 (instrinsic carrier concentration: 1.8x106 /cm3) • - impurity comes from source materials, carrier gases, process equipment, or • subtract handle • Extrinsic materials: • - n-type: III sub-lattice of III-V compound is substituted by V elements: impurity terms “donor” • - p-type: V sub-lattice of III-V compound is substituted by III elements: impurity terms “acceptor” http://www.siliconfareast.com/sigegaas.htm

  18. Optical fiber - lowest loss at 1.55 um - lowest dispersion” 1.3 um

  19. Energy band theory

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