1. 5335 Homepage: http://www.phys.ttu.edu/~cmyles/Phys5335/5335.html.
Introduction to Semiconductors Information from Kittel’s book (Ch. 8) + many outside sources.
Most lectures on semiconductors will be based on those prepared for
Physics 5335
Semiconductor Physics.
That course was taught last in the Fall
of It is scheduled to be taught
next in the Fall of 2012!! As
discussed at the start of the semester,
Phys clearly has overlap with
this Solid State course, but the 2
courses are complementary & are
NOT the same. I encourage you to
take Phys. 5335! More information
(last update, Dec., 2010!!) about
Phys is on the course webpage:
5335 Homepage:
5335 Lecture Page:

2. An Alternate Semiconductor Definition!

3. What is a Semiconductor? Kittel Ch. 8 & many other sources
Classification of Solids by their Conductivity/Resistivity (σ = conductivity, ρ = resistivity)
Metals: Good Conductors!
103 ≤ σ ≤ 108 (Ω-cm)-1 & ≤ ρ ≤ Ω-cm
Insulators: Poor Conductors!
σ ≤ 10-8 (Ω-cm)-1; ρ ≥ Ω-cm
Semiconductors/Semimetals:
10-8 ≤ σ ≤ 103 (Ω-cm)-1; ≤ ρ ≤ Ω-cm
Note the HUGE range!!
Note also that there are no rigid boundaries!

4. Semiconductors - Conductivity/Resistivity Definition
 Metals 
 Semimetals 

5. Semiconductors - Bandgap Definition
Semiconductors are ~ Small Bandgap Insulators
(we defined bandgap Eg earlier). Strictly speaking, a semicondcutor must also be capable of being doped (we’ll define doping later).
Typical Bandgaps Semiconductors: 0 ~ ≤ Eg ≤ ~ 3 eV Metals & Semimetals: Eg = 0 eV Insulators: Eg ≥ 3 eV
An Exception is Diamond: Eg = ~ 6 eV. Diamond 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!

6. More Semiconductor Characteristics
In pure materials (very rare):
The electrical conductivity σ  exp(cT)
T = Kelvin Temperature, c = constant
Impure materials (most):
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).

7. 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”)

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

9. The Periodic Table Cloth!

10. Group IV Elements & III-V & II-VI Compounds

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

12. Many Materials of Interest:
Have crystal lattice structures =
Diamond or Zincblende
(discussed in detail earlier!):
Each atom is tetrahedrally coordinated with four (4) nearest-neighbors.
The bonding is (mostly) sp3 hybrid bonding (strongly covalent).
Two atoms/unit cell (repeated to form an infinite solid).

13. 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

14. Zincblende/Diamond Lattices
The Cubic Unit Cell
Zincblende Lattice
The Cubic Unit Cell
Semiconductor Physicists & Engineers
need to know these structures!

15. Semiconductor Physicists & Engineers need to know these structures!
Diamond Lattice
Diamond Lattice
The Cubic Unit Cell
Semiconductor Physicists & Engineers
need to know these structures!

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

17. Some Materials of Interest:
Have crystal lattice structures =
Wurtzite Structure
(discussed in detail earlier!):
Similar to Zincblende, but has hexagonal symmetry instead of a cubic.
Each atom is tetrahedrally coordinated with four (4) nearest-neighbors.
The bonding is (mostly) sp3 hybrid bonding (strongly covalent).
Two atoms/unit cell (repeated to form an infinite solid).

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