semiconductor electronic devices eecs 321 spring 2002 cwruprof. dave smith crystal structures...
Post on 17-Jan-2016
213 Views
Preview:
TRANSCRIPT
Semiconductor Electronic Devices EECS 321 Spring 2002 CWRU Prof. Dave Smith
CRYSTALSTRUCTURES
LECTURE 5(18 slides)
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).
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
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?
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
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
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
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
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
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
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.
Semiconductor Electronic Devices EECS 321 Spring 2002 CWRU Prof. Dave Smith
CRYSTALGROWTH
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
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.
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
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
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
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.
top related