1. 1. Crystal Properties and Growth of Semiconductors
Electrical behavior of solids
Arrangement of atoms
1.1. Semiconductor Materials
Electrical conductivity intermediate between
metals and insulators

2. What distinguishes semiconductors? - resistance/resistivity
- crystalline structure
The resistance of a bar of material with dimensions L, W, t:
Resistivity  is:
metals:  < 10-3-cm
insulators:  >102-cm
semiconductors: 10-3-cm <  < 102-cm W t L

3. Figure 1: Electrical conductivities of some common materials.

4. *Conductivity of semiconductor material can be varied over orders of magnitude by changes in
-temperature
-optical excitation
-impurity content
Periodic table:
Column IV Si, Ge Elemental semiconductors
III-V Compound semiconductors example:GaAs
II-VI Compound semiconductors example:CdTe

5. The Portion of Periodic Table Where Semiconductors Occur

6. Binary compounds: GaAs, GaP, GaN, CdTe, InP etc.
Ternary compounds: AlGaAs, GaAsP, HgCdTe, etc.
Quaternary compounds: InGaAsP, AlGaInAs,etc.
Applications:
*transistors, integrated circuits (Si)
*light emitting diodes (LEDs) (GaAs,GaN, GaP)
*lasers (AlGaInAs, InGaAsP, GaAs, AlGaAs)
*light detectors(Si, InGaAsP, CdSe, InSb, HgCdTe)

7. Solids classified according to atomic arrangement: Crystalline
1.2. Crystal Lattices
Solids classified according to atomic arrangement:
Crystalline
Amorphous
Polycrystalline
 (a) Crystalline (b) Amorphous (c) Polycrystalline

8. The atoms making up the CRYSTAL
are arranged in a periodic fashion called LATTICE.
UNIT CELL is a representative of the entire lattice and is generally repeated throughout the structure.
PRIMITIVE CELL is the smallest unit cell that can be repeated to form the lattice.
Crystal lattice determines:
Density of solid (mechanical property)
Allowed energy bands of electrons (electrical property).

9. Cubic Lattices Simple (SC) Body-centered (BCC) Face-centered (FCC)
a – lattice constant

10. Diamond Lattice
Top view
Diamond lattice is an FCC plus placing atoms ¼ a, ¼ a, ¼ a (in x, y and z direction) from each atom in the FCC.
Construction of a diamond lattice from two interpenetrating FCC sublattices.

11. Diamond Lattice of Si from Different Angles of View

12. *Diamond (zincblende) lattice - typical of most of the commonly used semiconductors.
*Characteristic of Si, Ge, III-V compounds.
*Possible to vary the composition of alloy by choosing the fraction of numbers of the atoms, par example:
AlxGa1-xAs (x % of Al, (1-x)% of Ga)
InxGa1-xAsyP1-y

13. Conclusion
Atomic arrangement in certain planes in crystal is important to many of the mechanical, metallurgical, and chemical properties of the material.
Crystals cleaved along certain atomic planes, resulting in exeptionally planar surfaces
Chemical reactions-etching of a crytal often take place preferentially along certain directions