Semiconductor Electronic Devices EECS 321 Spring 2002 CWRUProf. Dave Smith CRYSTAL STRUCTURES...

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.