1. An Alternative Semiconductor Definition!

2. 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; ≤ ρ ≤ Ω-cm
Semiconductors & Semimetals:
10-8 ≤ σ ≤ 103 (Ω-cm)-1; ≤ ρ ≤ Ω-cm
NOTE THE HUGE RANGE!!
Insulators:
σ ≤ 10-8 (Ω-cm)-1; ρ ≥ Ω-cm
Actually, there are no rigid boundaries!

3. Polytetrafluoroethylene
Metals & Insulators: Measured resistivities range over more than 30 orders of magnitude!
Material
Resistivity (Ωm) (295K)
Resistivity (Ωm) (4K)
10-12
“Pure” Metals
Copper
10-5
Semiconductors
Ge (pure)
5  102
1012
Insulators
Diamond
1014
Polytetrafluoroethylene
(P.T.F.E)
1020
Potassium
2  10-6
10-10

4. Metals, Insulators & Semiconductors
At low temperatures,
all materials are
insulators or metals.
1020-
Diamond
1010-
Resistivity (Ωm)
Pure Metals:
Resistivity increases rapidly with increasing temperature.
Germanium
100 -
Copper
10-10-
100
200
300
Temperature (K)
Semiconductors:
Resistivity decreases rapidly with increasing temperature. Semiconductors have resistivities intermediate between metals and insulators at room temperature.

5. Semiconductors Conductivity/Resistivity Definition
 Metals 
 Semimetals 

6. Semiconductors Conductivity/Resistivity Definition
Note the wide
range of
conductivity!
 Metals 
 Semimetals 

7. Conductivity/Resistivity of Some Materials
Semiconductors!

8. Conductivity of Some Materials

9. One Way to Classify “Electronic Materials”

10. Typical Bandgaps Semiconductors: Band Gap Definition
Semiconductor ~ Small Band Gap 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!

11. 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):
σ depends strongly on impurity (doping) concentrations. “Doping” means to add impurities to change σ
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).

12. The Best Known Semiconductor is Silicon (Si)
But, there are HUNDREDS (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!” )

13. The Periodic Table: Group IV Materials + III-V & II-VI Compounds
Relevant Parts for Elemental & Binary Semiconductors
III IV V VI II
II
Group IV Materials + III-V & II-VI Compounds

14. Some Elements & Compounds which can be Semiconductors (Purple!)

15. Semiconductors (Main Constituents)

16. The Periodic Table Cloth!

17. Group IV Elements and III-V & II-VI Compounds

18. Group IV Elements III-V, II-VI, & IV-IV Compounds
Diamond
Lattice 
  Zincblende or Wurtzite Lattices  
Diamond
(α-Sn or gray tin)
    
Band gap (mostly) decreases &
near neighbor distance (mostly) increases within a row going from IV elements to III-V compounds to II-VI compounds.
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.

19. 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).

20. The Zincblende (ZnS) Lattice
Zincblende Lattice:
The Cubic Unit Cell.
If all atoms are the
same, itbecomes the
Diamond Lattice!
Zincblende Lattice:
A Tetrahedral
Bonding Configuration

21. Zincblende & Diamond Lattices
Zincblende Lattice
The Cubic Unit Cell
Diamond Lattice
The Cubic Unit Cell
Semiconductor Physicists & Engineers
need to know the geometry of these structures!

22. Semiconductor Physicists & Engineers need to know these structures!
Diamond Lattice
Diamond Lattice
The Cubic Unit C`ell.
Semiconductor Physicists & Engineers
need to know these structures!

23. Zincblende (ZnS) Lattice
Zincblende Lattice
The Cubic Unit Cell.

24. 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).

25. Semiconductor Physicists & Engineers need to know these structures!
Wurtzite Lattice
Semiconductor Physicists & Engineers
need to know these structures!

26. Room Temperature Properties of Some Semiconductor Materials

27. Room Temperature Properties of
Some Semiconductors

28. Lattice Constants of Some Semiconductors

29. Room Temperature Properties of Si, Ge, & GaAs