An Alternative Semiconductor Definition!
What is a Semiconductor?
B - Ch 1, Y - Ch 1, S - Ch 1
Conductivity/Resistivity Definition
(σ = conductivity, ρ = resistivity)
Metals: Good Conductors!
103 ≤ σ ≤ 108 (Ω-cm)-1;
10-8 ≤ ρ ≤ 10-3 Ω-cm
Semiconductors and Semimetals:
10-8 ≤ σ ≤ 103 (Ω-cm)-1;
10-3 ≤ ρ ≤ 108 Ω-cm
NOTE THE HUGE RANGE!!
Insulators:
σ ≤ 10-8 (Ω-cm)-1;
ρ ≥ 108 Ω-cm
Actually, there are no rigid boundaries!
Semiconductors
Conductivity/Resistivity Definition
 Metals 
 Semimetals 
Semiconductors: Bandgap Definition
Semiconductor ~ A small bandgap insulator
(We’ll define bandgap Eg in detail later). Strictly speaking, it must
also be capable of being doped (we’ll define doping in detail later).
Typical Bandgaps
Semiconductors: 0 ~ ≤ Eg ≤ ~ 3 eV
Metals & Semimetals: Eg = 0 eV
Insulators: Eg ≥ 3 eV
Exception  Diamond, with Eg = ~ 6 eV, is usually an
insulator, but it can be doped & used as a semiconductor!
Also, sometimes there is confusing terminology like
GaAs: Eg = 1.5 eV is sometimes called semi-insulating!
Some Semiconductor Characteristics
• In pure materials (which are very rare):
The electrical conductivity σ  exp(cT)
T = Kelvin Temperature, c = constant
• In impure materials (most materials):
– The electrical conductivity σ depends strongly on
impurity concentrations.
• “Doping” means to add impurities to change σ
– The electrical conductivity σ can be changed by light or
electron radiation & by injection of electrons at contacts
– Transport of charge can occur by the motion of
electrons or holes (defined later).
The Best Known Semiconductor is
Silicon (Si)
• However, there are HUNDREDS (maybe THOUSANDS) of others!
•
•
•
•
•
•
Elemental: Si, Ge, C (diamond)
Binary compounds: GaAs, InP, .
Organic compounds: (CH)n (polyacetyline)
Magnetic semiconductors: CdxMn1-xTe, …
Ferroelectric semiconductors: SbI, …
Superconducting compounds (!!)
GeTe, SrTiO3, .. ( “High Tc materials!” )
The Periodic Table:
The Relevant Parts for Elemental & Binary Semiconductors
III IV V VI
II
II
Group IV Materials & III-V & II-VI Compounds
The Periodic Table Cloth!
Group IV Elements and
III-V and II-VI Compounds
Diamond
Lattice

Group IV Elements
III-V, II-VI, & IV-IV Compounds
  Zincblende or Wurtzite Lattices  
Diamond





Band gap (mostly) decreases & 
near neighbor distance (mostly)

increases within a row going

from IV elements to III-V
compounds to II-VI compounds. 

(α-Sn or gray tin)
Band gap (mostly) decreases &
near neighbor distance (mostly)
increases going from IV elements
to III-V to II-VI compounds.
Band gap (mostly) decreases &
nearest neighbor distance (mostly)
increases going down a column.
Many Materials of Interest in This Course:
Have crystal lattice structures 
Diamond or Zincblende
(These will be discussed in detail again later!)
• In these structures, each atom is
tetrahedrally coordinated with four (4)
nearest-neighbors.
• The bonding between neighbors is (mostly)
sp3 hybrid bonding (strongly covalent).
• There are 2 atoms/unit cell
(repeated to form an infinite solid).
The Zincblende (ZnS) Lattice
Zincblende Lattice:
The Cubic Unit Cell.
If all atoms are the same,
it becomes the
Diamond Lattice!
Zincblende Lattice:
A Tetrahedral
Bonding Configuration
Zincblende & Diamond Lattices
Diamond Lattice
Zincblende Lattice
The Cubic Unit Cell
The Cubic Unit Cell
Semiconductor Physicists & Engineers
need to know these structures!
Diamond Lattice
Diamond Lattice
The Cubic Unit Cell.
Semiconductor Physicists & Engineers
need to know these structures!
Zincblende (ZnS) Lattice
Zincblende Lattice
The Cubic Unit Cell.
Some Materials of Interest in This Course
have crystal lattice structures 
Wurtzite Structure
(This will be discussed in detail again later!)
• This is similar to the Zincblende structure, but it has
hexagonal symmetry instead of cubic.
• In these structures, each atom is tetrahedrally
coordinated with four (4) nearest-neighbors.
• The bonding between neighbors is (mostly)
sp3 hybrid bonding (strongly covalent).
• There are 2 atoms/unit cell
(repeated to form an infinite solid).
Wurtzite Lattice
Semiconductor Physicists & Engineers
need to know these structures!
Room Temperature Properties of Some
Important Semiconductor Materials