ECE 874: Physical Electronics

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ECE 874Physical Electronics

• Prof. Virginia Ayres
• Electrical Computer Engineering
• Michigan State University
• ayresv_at_msu.edu

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Lecture 04, 11 Sep 12
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Example problem the surface of a Si wafer is a
(001) plane. Which, if any lt110gt directions are
perpendicular to the Si wafer (001) plane
direction?
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110
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110
Battery -
Principles of Electronic Devices, Streetman and
Bannerjee
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Convenient to know two directions
Crystalline direction lying within the surface plane (transport directions) Primary flat gives a lt110gt direction
Surface orientation 111 or 001 also gives n or p type Secondary flat
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Primary flat is a reference direction to help you
find any in-plane transport direction that you
want
Note that the directions are different for (1110
and (100) type orientations
110
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Example problem
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Example problem
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Example problem
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(a) 8 lt111gt type directions to the 8 facets
however Angles to top facets are all the same
values. Angles to bottom facets are all the same
values.
001
111
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(b) 4 pieces 4 top cleavage planes split open at
the pressure point
001
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(c) Now locate facet w.r.t in plane direction
001
111
110
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More about non-Si crystal structureswurtzite
and rock salt
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Motivation to study what crystal structures can
do
From The Economist 01-07 Sep 12 Technology
Quarterly Very recent recognition chalcogenides
have well-controlled crystalline versus amorphous
crystal structures as a function of pulsed
thermal energy. Very local 10 nm 1/0 states and
very low energy needed to switch between them.
It looks like chalcogenides are going to be the
next hot thing for flash drives with a lot of
capacity. From Wikipedia chalcogneides can
be Cadmium telluride Indium sulfide Zinc
telluride Sodium selenide Other
mixes Crystalline phase zinc blende, (Id check
wurtzite too)
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Recall the diamond crystal structure is formed
from two interpenetrating fcc lattices displaced
(¼, ¼, ¼)
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with only 4 of the atoms from the
interpenetrating fcc inside a single cubic Unit
cell.
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Wurtzite is formed from two interpenetrating
hexagonal close packed hcp lattices of different
atoms
3 S
7 Cd
7 S
3 Cd
3 S
7 Cd
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Wurtzite is formed from two interpenetrating
hexagonal close packed hcp lattices of different
atoms, inside a hexagonal Unit cell
hcp lattice 01
Note tetrahedral bonding inside
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Wurtzite is formed from two interpenetrating
hexagonal close packed hcp lattices of different
atoms, inside a hexagonal Unit cell
hcp lattice 02
Note tetrahedral bonding inside
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As per in-class demonstration with balls, hcp is
a very stable arrangement of atoms. Also
tetrahedral bonds fit well inside the hexagonal
Unit cell providing even more stability/balance
in very direction.
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Example problem what is the Number of equivalent
atoms inside the hexagonal Unit cell of height c
?
6 from dark contrast atoms (Pr. 1.3)
Also have a contribution from the
interpenetrating light contrast atoms
7 S
3 S
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How much of each light contrast atom is inside
all.
Total equivalent atoms from triangular
arrangement of light contrast atoms in hexagonal
Unit cell 3 x 1 3
(do the easy one first)
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Also have one inside atom in the middle of the
hexagonal layer 1
(do the next easiest one second)
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From the vertex atoms
Hexagonal In plane 1/3 inside
Hexagonal Interior plane Top to bottom all
inside 1
Therefore 1 vertex atom 1/3 X 1 1/3
inside 6 atoms x 1/3 each 2
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Total number of light and dark contrast atoms
inside hexagonal Unit cell 3 (1 (6x1/3
2) 6