semiconductor electronic devices eecs 321 spring 2002 cwruprof. dave smith crystal structures...
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![Page 1: Semiconductor Electronic Devices EECS 321 Spring 2002 CWRUProf. Dave Smith CRYSTAL STRUCTURES LECTURE 5 (18 slides)](https://reader035.vdocuments.us/reader035/viewer/2022062804/5697bf881a28abf838c8922e/html5/thumbnails/1.jpg)
Semiconductor Electronic Devices EECS 321 Spring 2002 CWRU Prof. Dave Smith
CRYSTALSTRUCTURES
LECTURE 5(18 slides)
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Semiconductor Electronic Devices EECS 321 Spring 2002 CWRU Prof. Dave Smith
x y
z up
Constructing an FCC crystal lattice
Note how the FCC is justifiably called cubic close-packed (CCP).
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Semiconductor Electronic Devices EECS 321 Spring 2002 CWRU Prof. Dave Smith
x
yz up
Homework 5: A base 2-D close-packed square lattice can be found in the both the SC and FCC lattices. The 3-D extension differs,Resulting in a close-packed cubic lattice for FCC but a much lessDense SC layout. BCC is also not close-packed. Can you find, in any plane of the BCC lattice, a 2D close-packed structure? Discuss the (111) plane in this regard. What is the plane that looks closest to the one below?
x
y
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Semiconductor Electronic Devices EECS 321 Spring 2002 CWRU Prof. Dave Smith
Building an FCC lattice in an obvious way
First layer Second layer Third layer
Note: certain planesclearly show HCPpatterns.
HOME: what plane is this?
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Semiconductor Electronic Devices EECS 321 Spring 2002 CWRU Prof. Dave Smith
Diamond and Zincblende Lattices
8-atom unit cellmade from FCC 4-atom unit cell by puttinganother atom ata/4+b/4+c/4 from each FCC atom
FCC
Zincblende lattice has different species in FCC sublattices: e.g. InP, GaAs
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Semiconductor Electronic Devices EECS 321 Spring 2002 CWRU Prof. Dave Smith
Analyzing the diamond lattice
FCC
BCC
Conclusion: the octantshown is an incompleteBCC lattice pattern. Use this in one of the HW’sRegarding packing fraction
Note: 4 bondshelps explain thatC forms a diamondlattice structure
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Semiconductor Electronic Devices EECS 321 Spring 2002 CWRU Prof. Dave Smith
Our favorite nine III-V binary semiconductors form zincblende lattices
As
Ga
Basic FCC lattice of Ga
FCC lattice for As
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Semiconductor Electronic Devices EECS 321 Spring 2002 CWRU Prof. Dave Smith
Again, thanks to some popsicle sticks, some Elmer’s glue anda bunch of Marbles from Michael’s Arts and Crafts Store, a digital camera and Photoshop software
HCP starting plane – builds up, but at each plane, one can choosedifferent sites for the triad – as shown above
Hexagonal Close Packing
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Semiconductor Electronic Devices EECS 321 Spring 2002 CWRU Prof. Dave Smith
HCP and FCC contain HCP-type planes
Hexagonal Close-Packed Cubic (FCC) Close-Packed
Top
vie
w
In fact, these lattice types have the same packing fraction.
Open (seen from above) all layers Closed within 3 layers
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Semiconductor Electronic Devices EECS 321 Spring 2002 CWRU Prof. Dave Smith
Crystalline Element Lattice Types
Reference: http://www.uis.edu/~trammel/sci/unit_cells/sld30.htm
III IV V VIII VII
BCC has 8 nearest neighbors
diamond lattices
HCP has 12 nearest neighbors
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Semiconductor Electronic Devices EECS 321 Spring 2002 CWRU Prof. Dave Smith
Streetman and Banerjee
6) 1.47) 1.78) 1.109) 1.14
Assigned Problems 5-8.
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Semiconductor Electronic Devices EECS 321 Spring 2002 CWRU Prof. Dave Smith
CRYSTALGROWTH
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Semiconductor Electronic Devices EECS 321 Spring 2002 CWRU Prof. Dave Smith
Czolchraski Crystal Growth Method
Ref: S&BFigs. 1.10,1.11
12” diameter by 1 meter Si bouleMade by pulling seed from Si melt
seed
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Semiconductor Electronic Devices EECS 321 Spring 2002 CWRU Prof. Dave Smith
Epitaxial Growth Methods
• LPE (Liquid Phase Epitaxy) – precipitation from liquid phase onto substrate, controlled by time and temperature
• VPE (Vapor Phase Epitaxy) – fast gas flow velocity over heated substrates; surface reaction of compounds releases desired atoms• MBE (Molecular Beam Epitaxy) – for monolayer-level control of stoichiometry – beams of elements to be deposited
Reference: Mandatory reading (hand out): E. D. Jungbluth, “Crystal Growth Methods Shape Communications Lasers,” Laser Focus World, vol. 29, pp. 61-72 (Feb., 1993).
Start with suitably oriented crystal substrate – grow layers of identical (homoepitaxy) or different material (heteroepitaxy) maintaining lattice type, orientation and lattice constant.
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Semiconductor Electronic Devices EECS 321 Spring 2002 CWRU Prof. Dave Smith
Epitaxial GrowthTechnologies
Reference: Mandatory reading (will hand out): E. D. Jungbluth, “Crystal Growth Methods Shape Communications Lasers,” Laser Focus World, vol. 29, pp. 61-72 (Feb., 1993).
LPE
VPE
MBE
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Semiconductor Electronic Devices EECS 321 Spring 2002 CWRU Prof. Dave Smith
Epitaxial Growth Methods
2” dia wafer cassette
InP-based laser substrate
Reference: E. D. Jungbluth, ibid.
Reference: G. P. Agrawal
2-D Lithography and etching at these stages
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Semiconductor Electronic Devices EECS 321 Spring 2002 CWRU Prof. Dave Smith
A superlattice of MBE-Grown Layers
Ref:S&BFig. 1.16
Alternating layersof GaAs (dark)and AlAs (light)with 4-monolayerperiodicity:
SUPERLATTICE
CBVB
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Semiconductor Electronic Devices EECS 321 Spring 2002 CWRU Prof. Dave Smith
Assignment 10.
Read. E. D. Jungbluth, “Crystal Growth Methods Shape Communications Lasers,” Laser Focus World, vol. 29, pp. 61-72 (Feb., 1993).
a) What is an acceptable substrate defect density?b) How would you hook up a DC battery to make Jungbluth’s Fig 1’s device lase? How would you convert it into a detector instead?c) Compare substrate heating techniques in the cases of LPE, VPE and MBE.d) Several different bandgap-engineered devices types are mentioned and they are more suitable for some techniques than others. Name one type suitable for each fab method and why is that method preferred? E.g.: use the figure right bottom.