semi-conductor theory

11/24/2013

CLASSIFICATIONS of MATERIALS

Semiconductor
Theory

a. Conductor

b. Semiconductor

c. Insulator

• Number of valence electrons is
1-3 with very high conductivity

• Number of valence electrons is 4 with intermediate conductivity

• Number of valence electrons is
5-8 with very low conductivity

Semiconductor
Conductors
• Has more electrons that are free to move
• Supports charge carriers to flow
• Support flow of electricity
• Has very low resistance allowing easy flow of electron current
• Has less than 4 valence electrons
– Examples: metals, electrolytes and ionized gases

Insulators
• Material with more than four valence electrons
• Extremely opposite characteristic to that of conductors
– Examples: mica, glass, and hard rubber

Semiconductors
• Has exactly four valence electrons
• Have electrical properties in between conductors and insulators

Energy Gap

Semiconductors are materials with conductivity that can be controlled through methods such as doping or changing the temperature. Conductivity can be increased through doping, creating either ptype semiconductors or n-type semiconductors.
Elementary Semiconductors:
Silicon (Si)
Germanium (Ge)
Compound Semiconductors:
Gallium Arsenide (GaAs)
Aluminum Arsenide (AlAs)
Gallium Phosphide (GaP

Intrinsic Material

• The wider the energy gap (Eg), the

harder the material to produce free electrons.
• Semiconductor that is free from impurities, such pure Silicon (Si) or Germanium (Ge)

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EXTRINSIC MATERIAL

• The characteristic of semiconductor can be altered by adding impurity through doping process (extrinsic material)
• Two type:
– N-type
– P-type

P-TYPE

N-TYPE
• N-type is created by introducing impurity elements that have five valence electrons (pentavalent)
–
antimony, arsenic, phosphorus
• Note that four covalent bonds are still present, however there is additional fifth electron due to
impurity