EE692

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EE692 Advanced Semiconductor Devices
Gong Gu
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Why Semiconductors?
Information processing (Amps, A/D, processors,
tranceivers)
Information acquisition (sensors)
Image, sound, temperature, pressure,
Image, sound, temperature, pressure,
Information transmission (wires, busses, cables,
optical fibers, or just air!)

• Brains and muscles of the system are made of
  semiconductors
• Metals dielectrics are used as transmission
  media
• Why?

Information processing (tranceivers, processors,
)
Displays
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Whats common for all the core components?
Light, sound, temperature, pressure,
Voltage, current
Vout
Vin
sensor
?A
Vout
Vin
Vin
Vout
output
input
Vin
Modulation of some physical quantity (output) by
some others Some kind of gain, conversion ratio,
sensitivity, etc
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Example Field-Effect Transistors
(FETs) Semiconductor vs Metal
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.
Vout
Vin
Vout
Vin
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!!!
FETs are building blocks.
G
D
S
Schematic illustration of a FET
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???
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A Digression The Vast Field of Electrical
Engineering

• Different disciplines are different levels of
  extraction
• Device engineers are at the junction of many
  disciplines
• Follow your passion

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A Digression The Vast Field of Electrical
Engineering

• But, each small field can consume ones 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! ?? ????? ?????
?????? ??
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A Digression The Vast Field of Electrical
Engineering
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.
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Lets 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?

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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

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Syllabus (Contd)

• Reference books
• Jasprit Singh, Physics of Semiconductors and
  Their Heterostructurs
• Reads like somebodys 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 DevicesBasic
  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.

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Syllabus (Contd)

• 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.

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Syllabus (Contd 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 its
  too late.
• The good news Its not that tough
• The population is too small. Any distribution
  does not have any statistical meaning. Which
  means, you could all get As. On the other hand,
  you could

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Back to Business
What are semiconductors, anyway???
Long way to go to answer this question.
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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

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Review of Semiconductor Physics
Quantum mechanics
A few things that we should cover but havent

• 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.

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• Spin
• The electron has an intrinsic angular momentum,
  with a value h/2.
• Along any direction, spin has two eigenvalues,
  h/2.

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Review of Semiconductor Physics
Quantum mechanics

• Homework
• Solve the Shrödinger eq for the following special
  cases
• 1D Infinitely deep well
• 1D Finite well
• 1D Harmonic oscillator
• 3D general well
• 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.
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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 Well 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.

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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 youll have a diffraction
pattern. Remember Bragg? That means periodicity
in the structure.
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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
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Fig. 4.2
Honeycomb