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

Periodic Table

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

Electron energy band diagram v.s. wave number

Energy bandgap v.s. lattice constant

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

Body-Centered Cubic (BCC) structure

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http://stokes.byu.edu/bcc.htm

e.g. iron, chromium, tungsten, niobium

Face-Centered Cubic (FCC) structure

•

http://stokes.byu.edu/fcc.htm

e.g.: aluminum, copper, gold, silver

Diamond Cubic (FCC) structure

• http://zh.wikipedia.org/zh-tw/File:Diamond_Cubic-F_lattice_animation.gif

Zincblende structure

• Diamond structure, Zincblende structure

e.g.: aluminum, GaAse.g.: Si, Ge

Atomic arrangement in different solids

Dislocation & strain

• Dislocation occurs 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

Strain semiconductor

• a) lattice match b) compressive strain c) tensile strain

• Strain offer flexibility for restriction of lattice mismatch

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)

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

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

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

Optical fiber

- lowest loss at 1.55 um- lowest dispersion” 1.3 um

Energy band theory