Semiconductors and Physical Operation of Diodes-2nm

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    ECE G201:

    Introductory Material Goal: to give you a quick, intuitive concept of

    how semiconductors, diodes, BJTs and

    MOSFETs work as a review of electronics and an overview of this

    course

    This discussion will be qualitative

    no equations for now, these will be added later

    Note that the concepts are often over-

    simplified!

    From Prof. J. Hopwood

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    Semiconductors and

    Physical Operation of Diodes Semiconductors

    Doping

    n-type material p-type material

    pn-Junctions

    forward, reverse, breakdown solar cells, LEDs, capacitance

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    Periodic Table of ElementsRelevant Columns: III IV V

    http://www.uky.edu/Projects/Chemcomics/html/hydrogen.htmlhttp://www.uky.edu/Projects/Chemcomics/html/helium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/lithium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/beryllium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/boron.htmlhttp://www.uky.edu/Projects/Chemcomics/html/carbon.htmlhttp://www.uky.edu/Projects/Chemcomics/html/nitrogen.htmlhttp://www.uky.edu/Projects/Chemcomics/html/oxygen.htmlhttp://www.uky.edu/Projects/Chemcomics/html/fluorine.htmlhttp://www.uky.edu/Projects/Chemcomics/html/neon.htmlhttp://www.uky.edu/Projects/Chemcomics/html/sodium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/magnesium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/aluminum.htmlhttp://www.uky.edu/Projects/Chemcomics/html/silicon.htmlhttp://www.uky.edu/Projects/Chemcomics/html/phosphorus.htmlhttp://www.uky.edu/Projects/Chemcomics/html/sulfur.htmlhttp://www.uky.edu/Projects/Chemcomics/html/argon.htmlhttp://www.uky.edu/Projects/Chemcomics/html/potassium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/calcium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/scandium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/titanium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/v.htmlhttp://www.uky.edu/Projects/Chemcomics/html/chromium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/manganese.htmlhttp://www.uky.edu/Projects/Chemcomics/html/iron.htmlhttp://www.uky.edu/Projects/Chemcomics/html/cobalt.htmlhttp://www.uky.edu/Projects/Chemcomics/html/nickel.htmlhttp://www.uky.edu/Projects/Chemcomics/html/copper.htmlhttp://www.uky.edu/Projects/Chemcomics/html/zinc.htmlhttp://www.uky.edu/Projects/Chemcomics/html/gallium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/germanium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/arsenic.htmlhttp://www.uky.edu/Projects/Chemcomics/html/selenium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/bromine.htmlhttp://www.uky.edu/Projects/Chemcomics/html/krypton.htmlhttp://www.uky.edu/Projects/Chemcomics/html/rubidium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/strontium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/yttrium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/zirconium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/niobium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/molybdenum.htmlhttp://www.uky.edu/Projects/Chemcomics/html/technetium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/ruthenium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/rhodium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/palladium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/silver.htmlhttp://www.uky.edu/Projects/Chemcomics/html/cadmium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/indium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/tin.htmlhttp://www.uky.edu/Projects/Chemcomics/html/antimony.htmlhttp://www.uky.edu/Projects/Chemcomics/html/tellurium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/iodine.htmlhttp://www.uky.edu/Projects/Chemcomics/html/xe.htmlhttp://www.uky.edu/Projects/Chemcomics/html/cesium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/barium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/hafnium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/tantalum.htmlhttp://www.uky.edu/Projects/Chemcomics/html/tungsten.htmlhttp://www.uky.edu/Projects/Chemcomics/html/rhenium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/osmium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/iridium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/platinum.htmlhttp://www.uky.edu/Projects/Chemcomics/html/gold.htmlhttp://www.uky.edu/Projects/Chemcomics/html/mercury.htmlhttp://www.uky.edu/Projects/Chemcomics/html/thallium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/lead.htmlhttp://www.uky.edu/Projects/Chemcomics/html/bismuth.htmlhttp://www.uky.edu/Projects/Chemcomics/html/polonium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/astatine.htmlhttp://www.uky.edu/Projects/Chemcomics/html/radon.htmlhttp://www.uky.edu/Projects/Chemcomics/html/francium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/radium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/rutherfordium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/dubnium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/seaborgium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/bohrium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/hassium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/meitnerium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/lanthanum.htmlhttp://www.uky.edu/Projects/Chemcomics/html/cerium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/praseodymium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/neodymium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/promethium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/samarium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/europium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/gadolinium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/terbium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/dysprosium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/holmium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/erbium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/thulium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/ytterbium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/lutetium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/actinium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/thorium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/protactinium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/uranium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/neptunium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/plutonium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/americium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/curium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/berkelium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/californium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/einsteinium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/fermium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/mendelevium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/nobelium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/lawrencium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/chlorine.html
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    The Silicon Atom

    Nucleus:14 protons14 neutrons

    10 core electrons:1s22s22p6

    -

    -

    -

    -

    4 valenceelectrons

    The 4 valence electrons are responsiblefor forming covalent bonds

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    Silicon CrystalEach Si atom has four nearest neighborsone for

    each valence electron

    0.5 nm

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    Two-dimensional Picture of Si

    note:each line () represents a valence electron

    covalent bond

    At T=0 Kelvin, all ofthe valence electrons

    are participating incovalent bonds

    There are no freeelectrons, therefore nocurrent can flow in thesilicon INSULATOR

    Si

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    Silicon at Room Temperature

    For T>0 K, the silicon atomsvibrate in the lattice. This is

    what we humans sense asheat.

    Occasionally, the vibrationscause a covalent bond to breakand a valence electron is freeto move about the silicon.

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    Silicon at Room Temperature

    -

    -

    For T>0 K, the silicon atomsvibrate in the lattice. This is

    what we humans sense asheat.

    Occasionally, the vibrationscause a covalent bond to breakand a valence electron is freeto move about the silicon.

    = free electron

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    Silicon at Room Temperature

    The broken covalent bond siteis now missing an electron.

    This is called a hole

    The hole is a missing negative

    charge and has a charge of +1.

    = a hole

    -

    +

    hole

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    Current Flow in Silicon

    *

    + -

    +-

    a bar of silicon

    I

    V

    Bond breakingdue to:-heat (phonons)-light (photons)

    Conductanceisproportional tothe number of

    electrons andholes:Si resistancedepends on temp.and light

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    Some important facts The number of electrons = the number of

    holes that is, n = p in pure silicon

    this is called intrinsic material High temp more electrons/holeslower

    resistance

    Very few electrons/holes at room

    temperature n=1.5x1010per cm3, but nSi= 5x10

    22per cm3

    n/nSi = 3x10-13(less than 1 in a trillion Si bonds

    are broken

    This is a SEMICONDUCTOR

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    Important Facts (cont.)

    Band Gap: energy required to break acovalent bond and free an electron E

    g

    = 0.66 eV (germanium)

    Eg= 1.12 eV (silicon)

    Eg= 3.36 eV (gallium nitride)

    Metals have Eg= 0

    very large number of free electrons

    highconductance

    Insulators have Eg> 5 eV almost NO free electrons zero conductance

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    Doping

    Intentionally adding impurities to asemiconductor to create more free electrons

    OR more holes (extrinsic material) n-type material

    more electrons than holes (n>p)

    p-type material

    more holes than electrons (p>n)

    HOW???

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    Periodic Table of ElementsRelevant Columns: III IVV

    http://www.uky.edu/Projects/Chemcomics/html/hydrogen.htmlhttp://www.uky.edu/Projects/Chemcomics/html/helium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/lithium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/beryllium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/boron.htmlhttp://www.uky.edu/Projects/Chemcomics/html/carbon.htmlhttp://www.uky.edu/Projects/Chemcomics/html/nitrogen.htmlhttp://www.uky.edu/Projects/Chemcomics/html/oxygen.htmlhttp://www.uky.edu/Projects/Chemcomics/html/fluorine.htmlhttp://www.uky.edu/Projects/Chemcomics/html/neon.htmlhttp://www.uky.edu/Projects/Chemcomics/html/sodium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/magnesium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/aluminum.htmlhttp://www.uky.edu/Projects/Chemcomics/html/silicon.htmlhttp://www.uky.edu/Projects/Chemcomics/html/phosphorus.htmlhttp://www.uky.edu/Projects/Chemcomics/html/sulfur.htmlhttp://www.uky.edu/Projects/Chemcomics/html/argon.htmlhttp://www.uky.edu/Projects/Chemcomics/html/potassium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/calcium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/scandium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/titanium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/v.htmlhttp://www.uky.edu/Projects/Chemcomics/html/chromium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/manganese.htmlhttp://www.uky.edu/Projects/Chemcomics/html/iron.htmlhttp://www.uky.edu/Projects/Chemcomics/html/cobalt.htmlhttp://www.uky.edu/Projects/Chemcomics/html/nickel.htmlhttp://www.uky.edu/Projects/Chemcomics/html/copper.htmlhttp://www.uky.edu/Projects/Chemcomics/html/zinc.htmlhttp://www.uky.edu/Projects/Chemcomics/html/gallium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/germanium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/arsenic.htmlhttp://www.uky.edu/Projects/Chemcomics/html/selenium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/bromine.htmlhttp://www.uky.edu/Projects/Chemcomics/html/krypton.htmlhttp://www.uky.edu/Projects/Chemcomics/html/rubidium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/strontium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/yttrium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/zirconium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/niobium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/molybdenum.htmlhttp://www.uky.edu/Projects/Chemcomics/html/technetium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/ruthenium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/rhodium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/palladium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/silver.htmlhttp://www.uky.edu/Projects/Chemcomics/html/cadmium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/indium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/tin.htmlhttp://www.uky.edu/Projects/Chemcomics/html/antimony.htmlhttp://www.uky.edu/Projects/Chemcomics/html/tellurium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/iodine.htmlhttp://www.uky.edu/Projects/Chemcomics/html/xe.htmlhttp://www.uky.edu/Projects/Chemcomics/html/cesium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/barium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/hafnium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/tantalum.htmlhttp://www.uky.edu/Projects/Chemcomics/html/tungsten.htmlhttp://www.uky.edu/Projects/Chemcomics/html/rhenium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/osmium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/iridium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/platinum.htmlhttp://www.uky.edu/Projects/Chemcomics/html/gold.htmlhttp://www.uky.edu/Projects/Chemcomics/html/mercury.htmlhttp://www.uky.edu/Projects/Chemcomics/html/thallium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/lead.htmlhttp://www.uky.edu/Projects/Chemcomics/html/bismuth.htmlhttp://www.uky.edu/Projects/Chemcomics/html/polonium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/astatine.htmlhttp://www.uky.edu/Projects/Chemcomics/html/radon.htmlhttp://www.uky.edu/Projects/Chemcomics/html/francium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/radium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/rutherfordium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/dubnium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/seaborgium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/bohrium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/hassium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/meitnerium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/lanthanum.htmlhttp://www.uky.edu/Projects/Chemcomics/html/cerium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/praseodymium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/neodymium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/promethium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/samarium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/europium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/gadolinium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/terbium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/dysprosium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/holmium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/erbium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/thulium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/ytterbium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/lutetium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/actinium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/thorium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/protactinium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/uranium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/neptunium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/plutonium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/americium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/curium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/berkelium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/californium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/einsteinium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/fermium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/mendelevium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/nobelium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/lawrencium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/chlorine.html
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    n-type siliconadd atoms from column Vof the periodic table

    Si

    P

    -

    Column V elements have 5valence electrons

    Four of the electrons form

    covalent bonds with Si, butthe 5thelectron is unpaired.

    Because the 5thelectron isweakly bound, it almost

    always breaks away from theP atom

    This is now a free electron.

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    VERY IMPORTANT POINT

    Si

    P+

    -

    The phosphorus atom hasdonatedan electron to thesemiconductor (Column Vatoms are called donors)

    The phosphorus is missing oneof its electrons, so it has apositive charge (+1)

    The phosphorus ion is bound

    to the silicon, so this +1charge cant move!

    The number of electrons is equal tothe number of phos. atoms: n = N

    d

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    Periodic Table of ElementsRelevant Columns: IIIIV V

    http://www.uky.edu/Projects/Chemcomics/html/hydrogen.htmlhttp://www.uky.edu/Projects/Chemcomics/html/helium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/lithium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/beryllium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/boron.htmlhttp://www.uky.edu/Projects/Chemcomics/html/carbon.htmlhttp://www.uky.edu/Projects/Chemcomics/html/nitrogen.htmlhttp://www.uky.edu/Projects/Chemcomics/html/oxygen.htmlhttp://www.uky.edu/Projects/Chemcomics/html/fluorine.htmlhttp://www.uky.edu/Projects/Chemcomics/html/neon.htmlhttp://www.uky.edu/Projects/Chemcomics/html/sodium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/magnesium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/aluminum.htmlhttp://www.uky.edu/Projects/Chemcomics/html/silicon.htmlhttp://www.uky.edu/Projects/Chemcomics/html/phosphorus.htmlhttp://www.uky.edu/Projects/Chemcomics/html/sulfur.htmlhttp://www.uky.edu/Projects/Chemcomics/html/argon.htmlhttp://www.uky.edu/Projects/Chemcomics/html/potassium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/calcium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/scandium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/titanium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/v.htmlhttp://www.uky.edu/Projects/Chemcomics/html/chromium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/manganese.htmlhttp://www.uky.edu/Projects/Chemcomics/html/iron.htmlhttp://www.uky.edu/Projects/Chemcomics/html/cobalt.htmlhttp://www.uky.edu/Projects/Chemcomics/html/nickel.htmlhttp://www.uky.edu/Projects/Chemcomics/html/copper.htmlhttp://www.uky.edu/Projects/Chemcomics/html/zinc.htmlhttp://www.uky.edu/Projects/Chemcomics/html/gallium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/germanium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/arsenic.htmlhttp://www.uky.edu/Projects/Chemcomics/html/selenium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/bromine.htmlhttp://www.uky.edu/Projects/Chemcomics/html/krypton.htmlhttp://www.uky.edu/Projects/Chemcomics/html/rubidium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/strontium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/yttrium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/zirconium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/niobium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/molybdenum.htmlhttp://www.uky.edu/Projects/Chemcomics/html/technetium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/ruthenium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/rhodium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/palladium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/silver.htmlhttp://www.uky.edu/Projects/Chemcomics/html/cadmium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/indium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/tin.htmlhttp://www.uky.edu/Projects/Chemcomics/html/antimony.htmlhttp://www.uky.edu/Projects/Chemcomics/html/tellurium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/iodine.htmlhttp://www.uky.edu/Projects/Chemcomics/html/xe.htmlhttp://www.uky.edu/Projects/Chemcomics/html/cesium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/barium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/hafnium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/tantalum.htmlhttp://www.uky.edu/Projects/Chemcomics/html/tungsten.htmlhttp://www.uky.edu/Projects/Chemcomics/html/rhenium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/osmium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/iridium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/platinum.htmlhttp://www.uky.edu/Projects/Chemcomics/html/gold.htmlhttp://www.uky.edu/Projects/Chemcomics/html/mercury.htmlhttp://www.uky.edu/Projects/Chemcomics/html/thallium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/lead.htmlhttp://www.uky.edu/Projects/Chemcomics/html/bismuth.htmlhttp://www.uky.edu/Projects/Chemcomics/html/polonium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/astatine.htmlhttp://www.uky.edu/Projects/Chemcomics/html/radon.htmlhttp://www.uky.edu/Projects/Chemcomics/html/francium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/radium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/rutherfordium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/dubnium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/seaborgium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/bohrium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/hassium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/meitnerium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/lanthanum.htmlhttp://www.uky.edu/Projects/Chemcomics/html/cerium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/praseodymium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/neodymium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/promethium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/samarium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/europium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/gadolinium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/terbium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/dysprosium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/holmium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/erbium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/thulium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/ytterbium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/lutetium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/actinium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/thorium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/protactinium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/uranium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/neptunium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/plutonium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/americium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/curium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/berkelium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/californium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/einsteinium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/fermium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/mendelevium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/nobelium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/lawrencium.htmlhttp://www.uky.edu/Projects/Chemcomics/html/chlorine.html
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    p-type siliconadd atoms from column IIIof the periodic table

    Si

    B

    Column III elementshave 3 valence electronsthat form covalent bondswith Si, but the 4thelectron is needed.

    This 4thelectron is takenfrom the nearby Si=Sibond

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    p-type siliconadd atoms from column IIIof the periodic table

    Si

    B

    Column III elementshave 3 valence electronsthat form covalent bondswith Si, but the 4thelectron is needed.

    This 4thelectron is takenfrom the nearby Si=Sibond

    This stolen electroncreates a free hole.

    hole

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    VERY IMPORTANT POINT

    Si

    B-

    +

    The boron atom has acceptedan electron from thesemiconductor (Column IIIatoms are called acceptors)

    The boron has one extraelectron, so it has a negativecharge (-1)

    The boron ion is bound to the

    silicon, so this -1 charge cantmove!

    The number of holes is equal tothe number of boron atoms: p = N

    a

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    The pn Junction

    p-type n-type

    anode cathode

    integrated circuit diode

    metalsilicon oxide

    doped siliconwafer (chip)

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    Dopant distribution inside a

    pn junction

    p>>n n>>p

    excess electrons diffuse

    to the p-type region

    excess holes diffuseto the n-type region

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    n~0, and donor ions

    are exposed

    Dopant distribution inside a

    pn junction

    excess electrons diffuse

    to the p-type region

    excess holes diffuseto the n-type region

    DEPLETION REGION:

    +

    p~0, and acceptor

    ions are exposed

    p>>n n>>p

    +

    ++-

    -

    -

    -

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    Voltage in a pn junction

    p>>n n>>p++

    +-

    --

    -x

    charge, r(x)

    x

    x

    electric field,E(x)

    voltage,V(x)

    +

    ~0.7 volts(for Si)

    x

    dxxxE

    0

    )(1

    )( r

    x

    dxxExV

    0

    )()(

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    Zero Bias

    p>>n n>>p++

    +-

    --

    xvoltage,V(x)

    ~0.7 volts(for Si)

    At zero bias (vD=0), very few electronsor holes can overcome this built-involtage barrierof ~ 0.7 volts (andexactly balanced by diffusion)

    iD= 0

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    Reverse Bias

    p>>n n>>p++

    +-

    --

    xvoltage,V(x)

    -5 volts

    As the bias (vD) becomes negative,the barrier becomes larger. Onlyelectrons and holes due to brokenbonds contribute to the diode current.

    iD= -Is

    vD

    0.0 volts

    1/2Is

    1/2Is

    Is

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    Breakdown

    p>>n n>>p++

    +-

    --

    xvoltage,V(x)

    -50 volts

    As the bias (vD) becomes very negative, thebarrier becomes larger. Free electrons and holesdue to broken bonds are accelerated to highenergy (>Eg) and break other covalent bondsgenerating more electrons and holes (avalanche).

    vD

    0.0 volts

    |I| >> Is

    large reverse current

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    Solar Cell (Photovoltaic)

    p>>n n>>p++

    +-

    --

    xvoltage,V(x)

    ~0.7 volts(for Si)

    Light hitting the depletion region causes acovalent bond to break. The free electron andhole are pushed out of the depletion region bythe built-in potential (0.7v).

    Rload

    light

    Iph

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    Light Emitting Diode (LED)

    p>>n n>>p++

    +-

    --

    xvoltage,V(x)

    2.0 volts

    In forward bias, an electron and holecollide and self-annihilate in thedepletion region. A photon with the gapenergy is emitted. Only occurs in some

    materials (not silicon).

    vD

    1.5 volts

    0.0 volts

    photon

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    Junction Capacitance

    p>>n n>>p

    +

    +

    +-

    -

    -

    Wn=p~0

    =11.9

    semiconductor-insulator-semiconductor

    The parasitic (unwanted) junction capacitance is

    Cj= eA/W, where W depends on the bias voltage

    A

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    Junction Capacitance (Cj) The junction capacitance must be charged

    and discharged every time the diode is turnedon and off

    Transistors are made of pn junctions. Thecapacitance due to these junctions limits thehigh frequencyperformance of transistors remember, Zc= 1/jwC becomes a short circuit at

    high frequencies (Zc0)

    this means that a pn junction looks like a short at

    high f This is a fundamental principle that limits the

    performance of all electronic devices