Transcript Slide 1

Why English is Important
• English ability would save life
http://www.youtube.com/watch?v=GT86iWiH2mI
• 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
What should you do to learn English in this class?
• 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
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
e.g.: aluminum, copper, gold, silver
•
http://stokes.byu.edu/fcc.htm
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,
e.g.: Si, Ge
Zincblende structure
e.g.: GaAs, and some many binary
compound semiconductors
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