• English ability would save life

• English ability gives you opportunities http://www.youtube.com/watch?v=tcseWVNmda8

e.g. Job opening in TSMC http://www.tsmc.com/chinese/careers/jobs.html

Why English is Important

http://www.youtube.com/watch?v=GT86iWiH2mI

• Read largely - preview textbook before class - review textbook and note after class

• Increase your vocabulary

• Invest your time to learn English regularly - Reading CNN, yahoo, newspaper

- Listening radio youtube watching TV

What should you do to learn English in this class?

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

Wavelength (Bandgap) Engineering

Reference article:http://www.tf.uni-kiel.de/matwis/amat/semi_en/kap_5/backbone/r5_1_4.html

Energy bandgap v.s. lattice constant

• Constrains for forming compound semiconductors: (1) requirement of lattice match, (2) availability of suitable substrates

• GaAs and InP are most common substrates used to grow up compound semiconductors (Note: InAs, InSb and GaSb substrates are availabe, but not as readily as GaAs and InP, moreover, all the ternary and quaternary alloys of interest are mis-matched to these substrates)• only InxGa1-xAs and InxAl1-xAs lattice-matched on InP substrate

• all AlxGa1-xAs can lattice-match on GaAs substrate

Bonding in solids

• Van der Waals bonding: attractions between atoms, molecules, and surfaces. e.g.: inert gas (like Ar), the ability of gecko to hang on a glass surface

• 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

•

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

Diamond structure v.s. Zincblende structure

• Diamond structure, Zincblende structure

e.g.: GaAs, and some many binary compound semiconductors

e.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 offers flexibility for restriction of lattice mismatch• Pseudomorphic: thin film take on morphology (lattice constant) of the substrate

Crystal Growth

• Bulk growth: - furnace growth - pulling technique e.g. Czochralski

• 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: epi and subtract are with different material

• Examples includes - 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 Compound 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 IV elements: impurity terms “donor” - p-type: V sub-lattice of III-V compound is substituted by IV elements: impurity terms “acceptor”

http://www.siliconfareast.com/sigegaas.htm

Optical fiber

- Silica optical fibers have a lowest loss at 1.55 um, and a lowest dispersion at 1.3 um

- In0.53Ga0.47As (Eg=0.47ev)/In0.52Al0.48As (Eg=1.45ev) heterojunction on InP can be used for optical fiber because Eg of InGaAs is close to 1.55 and 1.3 um

- Note: Why GaAs/AlGaAs can’t be used here?

Energy band theory