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The Ancient “Periodic Table”. A Quick Survey of the Periodic Table Consider the possible compounds formed by combining atoms from different columns of the periodic table. Ask the question : Which of these compounds are semiconductors ?.

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A Quick Survey of thePeriodic TableConsider the possible compounds formed by combining atoms from different columns of the periodic table.Ask the question: Which of these compounds are semiconductors?

group iv crystalline materials elemental semiconductors formed from atoms in column iv
Group IVCrystalline Materials Elemental Semiconductors formed from atoms in Column IV

C (carbon):Different Crystalline Phases

Diamond Structure:Diamond!

An insulator or semiconductor.

Graphite:Metallic!

The most common carbon solid.

Fullerenes: Based on Buckminsterfullerene:

“Bucky Balls”, Nanotubes, Insulators, Semiconductors,

or Metals depending on preparation.

Clathrates:Possible new forms of C solids?

Semiconductors or Semimetals, Compounds, Recent Research!!

slide4
Si (silicon): Different Crystalline Phases

Diamond Structure:A Semiconductor.

The most common Si solid.

Clathrates:“New” forms of Si solids.

Semiconductors, Semimetals, Compounds, Recent Research

Ge (germanium): Different Crystalline Phases

Diamond Structure:A Semiconductor.

The most common Ge solid.

Clathrates:“New” forms of Ge solids.

Semiconductors, Semimetals, Compounds, Recent Research

slide5
Sn (tin): Different Crystal Phases

Diamond Structure: Gray tin or α-Sn.

A Semimetal!

Body Centered Tetragonal Structure:

White tin or β-Sn. A Metal.

The most common Sn solid.

Clathrates:“New” forms of Sn solids.

Semiconductors, Semimetals, Compounds, Recent Research

Pb (lead):

Face Centered Cubic Structure:

A Metal.

slide6
Group IVMaterialsA Chemical Trend– Material Bandgap as a function of Near-Neighbor Distance for Diamond Structure Solids

Decreasing BandgapEgcorrelates with

Increasing Nearest-Neighbor Bond Lengthd

Atom Eg (eV) d (Å)

C 6.0 2.07

Si 1.1 2.35

Ge 0.7 2.44

Sn (a semimetal) 0.0 2.80

Pb(a metal) 0.0 1.63

Not the diamond

structure!

elemental semiconductors
Elemental Semiconductors
  • Mainly, these are from the Column IVelements

C (diamond), Si,Ge, Sn(gray tin or α-Sn)

The atoms are tetrahedrally bonded in the diamond crystal structureand each atom has 4 nearest-neighbors. Bonding:sp3covalent bonds.

  • Some Column V & Column VI elements are semiconductors:

P - A 3-fold coordinated lattice.

S, Se, Te5-fold coordinated lattices.

iii v compounds periodic table columns iii v
III-V CompoundsPeriodic Table Columns III & V

Column III Column V

B N

Al P

Ga As

In Sb

Tl not used Bi

Some possible compounds which

are semiconductors are:

BN, BP, BAs, AlN, AlP, AlAs, AlSb, GaN

GaP, GaAs, GaSb, InP, InAs, InSb,….

slide9
Some Applications of III-V Materials

IR detectors, LED’s, solid state lasers, switches, ….

BN, BP, BAs, AlN, AlP, AlAs, AlSb, GaN

GaP, GaAs, GaSb; InP, InAs, InSb,….

A Chemical Trend

The bandgap decreases& the interatomic distance increasesgoing down the periodic table. There is tetrahedral coordinationof the atoms. Many III-V compounds have the zincblende crystal structure. Some (B compounds & Ncompounds) have the wurtzite crystal structure. Interatomic Bonding:The bonds are not purely covalent! The charge separation due to the valence differences leads to Partially Ionic bonds.

ii vi compounds periodic table columns ii vi
II-VI CompoundsPeriodic Table Columns II & VI

Column II Column VI

Zn O

Cd S

Hg Se

Mn  sometimes Te

not used Po

Some possible compounds which are

semiconductors or semimetalsare:

ZnO, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS

HgSe, HgTe,… + some compounds with Mn….

slide11
Some Applications of II-VI Materials

IR detectors, LED’s, switches

ZnO, ZnS, ZnSe, ZnTe; CdS, CdSe, CdTe, HgS

HgSe, HgTe(semimetals) + some compounds with Mn

A Chemical Trend

The bandgap decreases& the interatomic distance increasesgoing down the periodic table. There is tetrahedral coordinationof the atoms. Except for the Hg compounds, which are semimetals with zero gaps, the II-VI materials have large bandgapscompared to the Column IV and the III-V materials. Some of these materials have a zincblende crystal stucture & some have wurtzite crystal structures. Interatomic Bonding:The charge separation due to the valence difference is large.

 The bonds are more ionic than covalent!

iv iv compounds periodic table column iv
IV- IV CompoundsPeriodic Table Column IV

Column IV

Binary combinations of

C, Si, Ge, Sn  SiC

Other compounds: GeC, SnC, SiGe, SiSn, GeSn,..

Cannot be made or cannot be made without species segregation or are not semiconductors. Two common crystalline phases forSiCare zincblende (a semiconductor), & hexagonal close packed (a large gap insulator).

There are also MANY other crystal

structures for SiC!

iv vi compounds periodic table columns iv vi
IV- VI CompoundsPeriodic Table Columns IV & VI

Column IV Column VI

C O

Si S

Ge Se

Sn Te

Pb

Some possible compounds which are

semiconductorsare: PbS, PbTe, PbSe, SnS .

Other compounds:SnTe, GeSe, .. can’t be made, can’t be made without segregation, or aren’t binary compounds, or aren’t semiconductors.

slide14
Some Applications of IV-VI Materials:

IR detectors, switches,…

PbS, PbTehave the zincblende crystal structure

Most others have 6-fold coordinated lattices.

The bonding is ~ 100% ionic

These materials have very small bandgaps, which makes them very useful as IR detectors

slide15

I-VII Compounds

Periodic Table Columns I & VII

  • These materials are mostly Ionic Insulators:

NaCl, KCl, CsCl, …

  • Their lattices do not have tetrahedral coordination. Most of them are 6- or 8-fold coordinated and have theNaClorCsClcrystal structures (discussed in any elementary Solid State Physics book).

The bonding is ~ 100% ionic

Their bandgaps are large

(which is why they are insulators!)

oxide compounds these are a category all their own
Oxide CompoundsThese are a category all their own
  • Most of these materials are

good insulatorswith large bandgaps.

  • A few are

Semiconductors: CuO, Cu2O, ZnO

  • Many of their properties are not very well understood.

Partially as a result of this there are relatively few applications.

An exception to this is ZnO, which has

wide use in ultrasonic transducers.

  • At low T, some oxides are superconductors

Many “high”Tcsuperconductors are based on

La2CuO4 (Tc~ 135K)

some other semiconductor materials
Some OtherSemiconductor Materials
  • “Alloy” mixturesof elemental materials(binary alloys):

SixGe1-x ,... (0 ≤ x ≤ 1)

  • “Alloy” mixtures of binary compounds (ternary alloys):

Ga1-xAlxAs, GaAs1-xPx,… (0 ≤ x ≤ 1)

  • “Alloy” mixturesof binary compounds with mixtures on both sublattices (quaternary alloys):

Ga1-xAlxAs1-yPy, .., (0 ≤ x ≤ 1, 0 ≤ y ≤ 1)

  • In the growth process, x & y can be varied, which varies the material bandgap & other properties.

“BANDGAP ENGINEERING!”

exotic semiconductors
“Exotic” Semiconductors

Layered Compounds:PbI2, MoS2, PbCl2, …

  • These materials have strong Covalent Bondingwithin each layer & weak Van Der Waals bonding between layers.
  • This means that they are effectively

“2 dimensional solids”

  • That is, their electronic & vibrational properties have a

~ 2 dimensional character.

Organic Semiconductors:Polyacetyline(CH2)nand other polymers

  • “These materials show great promise for future applications”

(I’ve heard this for  35 years!)

Many of these materials are not well understood

slide19

Other Semiconductors

Magnetic Semiconductors

  • Compounds with Mn and/or Eu(& other magnetic ions)
  • These are simultaneously semiconducting & magnetic

EuS, CdxMn1-xTe, Optical modulators,…

Others (see YC, p 4)

I-II-(VI)2 & II-IV-(V)2compounds

AgGaS2, ZnSiP2,…., Tetrahedral bonding

V2-(VI)3compounds

As2Se3….