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?
Group IV Crystalline 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!!
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
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.
Group IV Materials
A Chemical Trend – Material Bandgap as a function of
Near-Neighbor Distance for Diamond Structure Solids
Decreasing Bandgap Eg correlates with
Increasing Nearest-Neighbor Bond Length d
Atom
Eg (eV)
C
6.0
Si
1.1
Ge
0.7
Sn (a semimetal) 0.0
Pb (a metal)
0.0
Not the diamond
structure!
d (Å)
2.07
2.35
2.44
2.80
1.63
Elemental Semiconductors
• Mainly, these are from the Column IV elements
C (diamond), Si,Ge, Sn (gray tin or α-Sn)
The atoms are tetrahedrally bonded in the
diamond crystal structure and each atom has 4
nearest-neighbors. Bonding: sp3 covalent bonds.
• Some Column V & Column VI elements are
semiconductors:
P - A 3-fold coordinated lattice.
S, Se, Te 5-fold coordinated lattices.
III-V Compounds
Periodic 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,….
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
increases going down the periodic table. There is
tetrahedral coordination of the atoms. Many III-V
compounds have the zincblende crystal structure.
Some (B compounds & N compounds) 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
Column II
Column VI
Zn
O
Cd
S
Hg
Se
Mn  sometimes
Te
not used 
Po
Some possible compounds which are
semiconductors or semimetals are:
ZnO, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS
HgSe, HgTe,… + some compounds with Mn….
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 increases
going down the periodic table. There is tetrahedral coordination of
the atoms. Except for the Hg compounds, which are semimetals with
zero gaps, the II-VI materials have large bandgaps compared 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
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 for SiC are 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
Column IV
Column VI
C
O
Si
S
Ge
Se
Sn
Te
Pb
Some possible compounds which are
semiconductors are: 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.
Some Applications of IV-VI Materials:
IR detectors, switches,…
PbS, PbTe have 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
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
the NaCl or CsCl crystal 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
• Most of these materials are
good insulators with 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” Tc superconductors are based on
La2CuO4 (Tc~ 135K)
Some Other Semiconductor Materials
• “Alloy” mixtures of elemental materials (binary alloys):
SixGe1-x ,... (0 ≤ x ≤ 1)
• “Alloy” mixtures of binary compounds (ternary alloys):
Ga1-xAlxAs, GaAs1-xPx,… (0 ≤ x ≤ 1)
• “Alloy” mixtures of 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
Layered Compounds: PbI2, MoS2, PbCl2, …
• These materials have strong Covalent Bonding within 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)n
and 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
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)2 compounds
AgGaS2, ZnSiP2, …., Tetrahedral bonding
V2-(VI)3 compounds
As2Se3….