Transcript Semiconductor Electronic Devices

CRYSTAL
STRUCTURES
LECTURE 5
(18 slides)
Semiconductor Electronic Devices EECS 321 Spring 2002 CWRU
Prof. Dave Smith
Constructing an FCC crystal lattice
z =up
x
y
Note how the FCC is justifiably called cubic close-packed (CCP).
Semiconductor Electronic Devices EECS 321 Spring 2002 CWRU
Prof. Dave Smith
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 less
Dense 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?
z =up
y
y
x
Semiconductor Electronic Devices EECS 321 Spring 2002 CWRU
x
Prof. Dave Smith
Building an FCC lattice in an obvious way
First layer
Second layer
Third layer
Note: certain planes
clearly show HCP
patterns.
HOME: what plane is this?
Semiconductor Electronic Devices EECS 321 Spring 2002 CWRU
Prof. Dave Smith
Diamond and Zincblende Lattices
8-atom unit cell
made from
FCC 4-atom unit
cell by putting
another atom at
a/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
Note: 4 bonds
helps explain that
C forms a diamond
lattice structure
BCC
Conclusion: the octant
shown is an incomplete
BCC lattice pattern. Use this
in one of the HW’s
Regarding packing fraction
Semiconductor Electronic Devices EECS 321 Spring 2002 CWRU
Prof. Dave Smith
Our favorite nine III-V binary
semiconductors form zincblende lattices
Basic FCC
lattice of Ga
As
FCC lattice
for As
Ga
Semiconductor Electronic Devices EECS 321 Spring 2002 CWRU
Prof. Dave Smith
Hexagonal Close Packing
Again, thanks to some popsicle sticks, some Elmer’s glue and
a 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 choose
different sites for the triad – as shown above
Semiconductor Electronic Devices EECS 321 Spring 2002 CWRU
Prof. Dave Smith
HCP and FCC contain HCP-type planes
Top view
Hexagonal Close-Packed Cubic (FCC) Close-Packed
Open (seen from above) all layers
Closed within 3 layers
In fact, these lattice types have the same packing fraction.
Semiconductor Electronic Devices EECS 321 Spring 2002 CWRU
Prof. Dave Smith
Crystalline Element Lattice Types
II
HCP has 12
nearest neighbors
III IV V VI VII
diamond
lattices
BCC has 8
nearest neighbors
Reference: http://www.uis.edu/~trammel/sci/unit_cells/sld30.htm
Semiconductor Electronic Devices EECS 321 Spring 2002 CWRU
Prof. Dave Smith
Assigned Problems 5-8.
Streetman and Banerjee
6)
1.4
7)
1.7
8)
1.10
9)
1.14
Semiconductor Electronic Devices EECS 321 Spring 2002 CWRU
Prof. Dave Smith
CRYSTAL
GROWTH
Semiconductor Electronic Devices EECS 321 Spring 2002 CWRU
Prof. Dave Smith
Czolchraski Crystal Growth Method
seed
12” diameter by 1 meter Si boule
Made by pulling seed from Si melt
Ref: S&B
Figs. 1.10,1.11
Semiconductor Electronic Devices EECS 321 Spring 2002 CWRU
Prof. Dave Smith
Epitaxial Growth Methods
Start with suitably oriented crystal substrate – grow layers of
identical (homoepitaxy) or different material (heteroepitaxy)
maintaining lattice type, orientation and lattice constant.
• 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).
Semiconductor Electronic Devices EECS 321 Spring 2002 CWRU
Prof. Dave Smith
Epitaxial Growth
Technologies
LPE
MBE
VPE
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).
Semiconductor Electronic Devices EECS 321 Spring 2002 CWRU
Prof. Dave Smith
Epitaxial Growth Methods
2” dia wafer cassette
InP-based laser substrate
2-D Lithography
and etching at
these stages
Reference: G. P. Agrawal
Reference: E. D. Jungbluth, ibid.
Semiconductor Electronic Devices EECS 321 Spring 2002 CWRU
Prof. Dave Smith
A superlattice of MBE-Grown Layers
Alternating layers
of GaAs (dark)
and AlAs (light)
with 4-monolayer
periodicity:
SUPERLATTICE
CB
VB
Ref:
S&B
Fig. 1.16
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.
Semiconductor Electronic Devices EECS 321 Spring 2002 CWRU
Prof. Dave Smith