SEMICONDUCTOR

SEMICONDUCTOR

1. INTRINSIC SEMICONDUCTOR

   • An intrinsic semiconductor, also called an un doped semiconductor or i-type semiconductor, is a pure semiconductor without any significant dopant species present.
     • Pure form of semiconductors.

2. EXTRINSIC SEMICONDUCTOR

   • An extrinsic semiconductor is one that has been doped, that is, into which a doping agent has been introduced, giving it different electrical properties than the intrinsic (pure) semiconductor.
     • Impurities are added to improve conductivity.

3. ATOMIC STRUCTURE

   • BOHR'S ATOMIC THEORY
     • * According to Bohr's, atoms have a planetary structure that consists of a central nucleus, surrounded by orbiting electrons. * Nucleus contains protons and neutrons. * Electrons orbit the nucleus.
       • * The orbit paths of the electrons surrounding the nucleus are called shells. * Each shell has a defined number of electrons it will hold (2n2). * n=1,2,3,.......
         • * The outer shell is called the valence shell and electrons at this layer are called valence electrons. * Maximum number of valence electron is 8. * The material is more conductive if less electron valence orbiting the outer shell

4. MATERIAL CLASSIFICATION

   • CONDUCTOR
     • Low resistance which allows electrical current flow.
       • Charge flows freely
         • Copper, silver, gold, aluminum, nickel etc
   • SEMICONDUCTOR
     • Can allow or suppress electrical current flow.
     • Conductivity lies between conductor and insulator.
     • Carbon, silicon, germanium etc
   • INSULATOR
     • High resistance which suppresses electrical current flow.
     • Almost no charge flows.
     • Glass, ceramic, plastic, wood etc.

5. ENERGY BAND

   • SEMICONDUCTOR
     • Enables some electrons with enough energy to jump from the valence band to the conduction band easily.
       • Temperature Low - No free electron in the conduction band,
         • Temperature High - Electric conductivity high.
           • When potential difference is connected, the holes and electrons move in opposite directions.
             • Large number of electrons being excited into the conduction band, leaving a large number of holes in valence band.
   • INSULATOR
     • Valence Band - Filled with electrons
       • Conduction Band - Empty
         • Band Gap - Empty
           • Electrons are unable to gain enough energy to jump from the valence band to the conduction band
   • CONDUCTOR
     • Occupied by many conduction electron, causing metal to become good electric conductor.

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