SEMICONDUCTOR

SEMICONDUCTOR

1. Bohr’s Atomic Theory

   • •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, …..
         • Example: Copper: 2.8.18.1 Electron valence: 1
   • 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.

2. Periodic Table

3. Material Classification

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

4. Semiconductor

   • Extrinsic
     • Impuruties are added to improved semiconduvtivity
       • Dopping Process
         • N-type (Pentavalant)
         • P-type (Trivalant)
   • Intrinsic
     • Pure form of semiconductir

5. Energy Band

   • Conductor
     • 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.
   • 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 the valence band.
   • Insulator
     • Occupied by many conduction electrons, causing metal to become good electric conductor.

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