Date post: | 02-Jun-2018 |
Category: |
Documents |
Upload: | prazara2637 |
View: | 222 times |
Download: | 0 times |
of 32
8/10/2019 Semiconductors and Physical Operation of Diodes-2nm
1/32
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
8/10/2019 Semiconductors and Physical Operation of Diodes-2nm
2/32
Semiconductors and
Physical Operation of Diodes Semiconductors
Doping
n-type material p-type material
pn-Junctions
forward, reverse, breakdown solar cells, LEDs, capacitance
8/10/2019 Semiconductors and Physical Operation of Diodes-2nm
3/32
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.html8/10/2019 Semiconductors and Physical Operation of Diodes-2nm
4/32
The Silicon Atom
Nucleus:14 protons14 neutrons
10 core electrons:1s22s22p6
-
-
-
-
4 valenceelectrons
The 4 valence electrons are responsiblefor forming covalent bonds
8/10/2019 Semiconductors and Physical Operation of Diodes-2nm
5/32
Silicon CrystalEach Si atom has four nearest neighborsone for
each valence electron
0.5 nm
8/10/2019 Semiconductors and Physical Operation of Diodes-2nm
6/32
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
8/10/2019 Semiconductors and Physical Operation of Diodes-2nm
7/32
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.
8/10/2019 Semiconductors and Physical Operation of Diodes-2nm
8/32
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
8/10/2019 Semiconductors and Physical Operation of Diodes-2nm
9/32
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
8/10/2019 Semiconductors and Physical Operation of Diodes-2nm
10/32
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
8/10/2019 Semiconductors and Physical Operation of Diodes-2nm
11/32
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
8/10/2019 Semiconductors and Physical Operation of Diodes-2nm
12/32
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
8/10/2019 Semiconductors and Physical Operation of Diodes-2nm
13/32
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???
8/10/2019 Semiconductors and Physical Operation of Diodes-2nm
14/32
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.html8/10/2019 Semiconductors and Physical Operation of Diodes-2nm
15/32
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.
8/10/2019 Semiconductors and Physical Operation of Diodes-2nm
16/32
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
8/10/2019 Semiconductors and Physical Operation of Diodes-2nm
17/32
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.html8/10/2019 Semiconductors and Physical Operation of Diodes-2nm
18/32
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
8/10/2019 Semiconductors and Physical Operation of Diodes-2nm
19/32
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
8/10/2019 Semiconductors and Physical Operation of Diodes-2nm
20/32
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
8/10/2019 Semiconductors and Physical Operation of Diodes-2nm
21/32
The pn Junction
p-type n-type
anode cathode
integrated circuit diode
metalsilicon oxide
doped siliconwafer (chip)
8/10/2019 Semiconductors and Physical Operation of Diodes-2nm
22/32
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
8/10/2019 Semiconductors and Physical Operation of Diodes-2nm
23/32
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
+
++-
-
-
-
8/10/2019 Semiconductors and Physical Operation of Diodes-2nm
24/32
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
)()(
8/10/2019 Semiconductors and Physical Operation of Diodes-2nm
25/32
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
8/10/2019 Semiconductors and Physical Operation of Diodes-2nm
26/32
8/10/2019 Semiconductors and Physical Operation of Diodes-2nm
27/32
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
8/10/2019 Semiconductors and Physical Operation of Diodes-2nm
28/32
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
8/10/2019 Semiconductors and Physical Operation of Diodes-2nm
29/32
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
8/10/2019 Semiconductors and Physical Operation of Diodes-2nm
30/32
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
8/10/2019 Semiconductors and Physical Operation of Diodes-2nm
31/32
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
8/10/2019 Semiconductors and Physical Operation of Diodes-2nm
32/32
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