Transcript ECE692_1_1008

EE692
Advanced Semiconductor Devices
Gong Gu
Why Semiconductors?
Image, sound,
temperature,
pressure, …
Information
acquisition
(sensors)
Information
processing
(Amps, A/D,
processors,
tranceivers…)
Information transmission
(wires, busses, cables, optical fibers, or just air!)
Information
processing
(tranceivers,
processors, …)
• Brains and muscles of the
system are made of
semiconductors
Displays
• Metals & dielectrics are used as
transmission media
• Why?
What’s common for all the core components?
Light, sound,
temperature,
pressure, …
Voltage,
sensor current
Vin
Vin
A
Vout
Vout
output
Vout
input
Modulation of some physical quantity (output) by some others
Some kind of gain, conversion ratio, sensitivity, etc
Vin
Example: Field-Effect Transistors (FETs)
Semiconductor vs Metal
Vout
Vout
Vin
Vin
FET’s are building blocks.
G
S
D
Schematic illustration of a FET
For SiO2 dielectric, breakdown field Eb ~ 107 V/cm.
No matter how thick it is, the maximum induced
carrier area density is r0Eb/q = 2 × 1013 /cm2.
For a 1 m thick Si channel,
ni = 1.45 × 1010 /cm3,
the background carrier area density is
ni × 104 cm = 1.45 × 106 /cm2.
In principle, the area carrier density, and therefore
the channel conductance, can be modulated by 7
orders of mag!!!
For Al, n = 1.8 × 1023 /cm3. Even for 1 nm thin (monolayers!) Al, the background carrier
area density is 1.8 × 1016 /cm2. The conductance can only be modulated by 0.1%!!!
What are semiconductors, anyway???
A Digression: The Vast Field of Electrical Engineering
chemistry
Economics
Semiconductor
processing
Materials
science
Information theory
Solid- Semiconductor Device
state
physics physics
physics
circuits
Transistor
level
Higher
level
Control theory
Core knowledge body of the device engineer
• Different disciplines are different levels of extraction
• Device engineers are at the junction of many disciplines
• Follow your passion
A Digression: The Vast Field of Electrical Engineering
chemistry
Economics
Semiconductor
processing
Materials
science
Information theory
Solid- Semiconductor Device
state
physics physics
physics
circuits
Transistor
level
Higher
level
Control theory
Core knowledge body of the device engineer
• But, each small field can consume one’s entire life
• So, how can one be a good device engineer???
Chuang Tzu: My life is limited while knowledge is unlimited. Pursuing the unlimited
with the limited, it is just hopeless!
莊子： 吾生也有涯 而知也無涯 以有涯逐無涯 殆矣
A Digression: The Vast Field of Electrical Engineering
chemistry
Economics
Semiconductor
processing
Materials
science
Information theory
Solid- Semiconductor Device
state
physics physics
physics
circuits
Transistor
level
Higher
level
Control theory
Core knowledge body of the device engineer
How can one be a good device engineer???
The big picture!
This course is about the big picture.
It willed be tailored to suit your research interest; we have a small class
after all.
Let’s get to know each other!
• Name, year
• Previous exposure to quantum mechanics, solid-state physics, device
physics, processing, ckt design (courses + hands-on)
• Advisor
• Research field, particular topic
• Like it?
Syllabus
Course Objective:
To provide students with an understanding of device physics and advanced
semiconductor device concepts.
Topics
• Review of Semiconductor physics
- Crystal structure, band structures, band structure modification by alloys,
heterostructurs, and strain
- Carrier statistics
- Scattering, defects, phonons, mobility, transport in heterostructures
• Device concepts
- MOSFETs, MESFETs, MODFETs, TFTs
- Heterojunction bipolar transistors (HBT)
- Semiconductor processing
- Photodiodes, LEDs, semiconductor lasers
- (optional) resonant tunneling devices, quantum interference devices,
single electron transistors, quantum dot computing, ...
- Introduction to nanoelectronics
Syllabus (Cont’d)
Reference books
• Jasprit Singh, Physics of Semiconductors and Their Heterostructurs
Reads like somebody’s notes. May not be the most elegant or strict from a physics point of
view, but definitely serves semiconductor folks well. Intriguing and stimulating.
• Jasprit Singh, Semiconductor Devices:Basic Principles
Book by the same author on Devices but including semiconductor physics & processing.
• U. K. Mishra & J. Singh, Semiconductor Device Physics and Design
E-book available on line thru UT Lib.
• Karl Hess, Advanced Theory of Semiconductor Devices
Thin, but covers lots of stuff at advanced levels
• Ben Streetman, Solid State Electronic Devices
From basic physics to device concepts. Oldie goodie.
• S. M. Sze, Physics of Semiconductor Devices
The “Bible” of device enginees. Not for beginners. Keep it in mind or on your shelf; an
excellent reference book for your future career.
• R. S. Muller & T. I. Kamins, Device Electronics for Integrated Circuits
An undergrad textbook on Si microelectronics, but good to have. I go back to it quite often.
• J. D. Plummer, M. D. Deal, P. B. Griffin, Silicon VLSI technology: fundamentals,
practice and modeling
Best textbook on processing, by the people who developed many of the models.
Syllabus (Cont’d)
Journals
• IEEE Electron Device Letters
• IEEE Transactions on Electron Devices
• Applied Physics Letters
• Journal of Applied Physics
Websites
• Wikipedia (Are you kidding? No!)
• Ioffe Physico-Technical Institute
http://www.ioffe.ru/SVA/NSM/
http://www.ioffe.ru/SVA/NSM/Semicond/index.html
Physical properties of many semiconductors.
Syllabus (Cont’d: The Tough Part)
Evaluation
• Classroom participation, performance (15%)
• Homework / Mini projects – simple (20%)
• Term project: critical review of a selected paper, oral presentation on the topic of
the paper, oral exam (65%)
The topic may or may not be closely related to your research, but cannot be
your research topic per se. Need my okay on the topic before it’s too late.
• The good news: It’s not that tough
- …
- The population is too small. Any distribution does not have any statistical
meaning. Which means, you could all get A’s. On the other hand, you could
…
Back to Business
What are semiconductors, anyway???
Long way to go to answer this question.
Review of Semiconductor Physics
Quantum mechanics
• Shrödinger equation
The equation that scared Einstein
• Stationary states
• Special case: free space
• E-k dispersion: light wave vs de Broglie wave
• The concept of eigenstates
• Wave packets
• The uncertainty principle
Review of Semiconductor Physics
Quantum mechanics
A few things that we should cover but haven’t:
• Bound states
• Atoms; Coulomb potential
• Normalization of bound state wavefunctions
• Unbound states
• Difficulty of normalization of unbound states and the way around it
• i vs. j; physics vs. EE
• More quantum mechanics jargons you need to know
- Eigenstates
- Operators, eigenvalues
Solving Shrödinger Eq is to find the eigenvalues of the Hamiltonian operator.
- Spin
The electron has an intrinsic angular momentum, with a value ħ/2.
Along any direction, spin has two eigenvalues, ± ħ/2.
Review of Semiconductor Physics
Quantum mechanics
Homework
Solve the Shrödinger eq for the following special cases:
1. 1D Infinitely deep well
2. 1D Finite well
3. 1D Harmonic oscillator
4. 3D general well
5. Barrier tunneling
For 1., complete the math, visualize results, draw analogy with the electromagnetic
resonant cavity.
For 2., find and read thru the math in a book, visualize results, compare to dielectric
cavity or waveguide
For 3., find and read thru the math in a book, visualize results; compare to the
above and get some sense of how energy level spacing is related to the shape of
the potential.
For 4., generalize and visualize as much as you can.
For 5., visualize results and discuss physical meanings.
Review of Semiconductor Physics
Solid-state physics
The daunting task of solid state physics
• Quantum mechanics gives us the fundamental equation
• The equations are only analytically solvable for a handful of special cases
• One cannot solve the equations for more than two bodies!
• Solid-state physics is about many-body problems
There are 5 × 1022 atoms/cm3 in Si
Si atom: 1s22s22p63s23p2
Core: Nueclear + 1s22s22p6, Valence electrons: 3s23p2
We’ll come back to this later
Each particle is in the potential of all the other particles, which depends on
their positions, which must solved from the equation…
You have an equation with ~1023 unknows to solve. Mission impossible!
• Solid state physic is all about approximations.
Review of Semiconductor Physics
Crystal structures
If we assume the atomic cores have known and fixed positions, we only need to solve
the equations for the valence electrons. Life much easier!
Static lattice approximation
• Justification
• Related/similar approximation: Born-Oppenheimer
Crystal structures
If you shine X-ray on a piece of solid, very likely you’ll have a diffraction pattern.
Remember Bragg?
That means periodicity in the structure.
Review of Semiconductor Physics
Crystal structures
Bravais Lattices
A mathematical concept:
• No boundary or surface
• No real (physical) thing – just points, hence no defects
• No motion
Unit cells (or primitive unit cells)
The smallest unit that repeats itself.
Fig. 4.10
Fig. 4.2
Honeycomb