SEMICONDUCTOR

SEMICONDUCTOR

1. STRUCTURE ATOM

   • Bohr's Atomic Theory
     • According to Bohr, atoms have a planetary structure that consists of a central nucleus, surrounded by orbiting electrons.
     • The orbit paths of the electrons surrounding the nucleus are called shells. • Each shell has a defined number of electrons it will hold (2n 2 ). • 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.

2. 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

3. 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
     • Types of Extrinstic Semiconductor
       • P- Type (Trivalant)
         • Dopping Process
       • N- Type ( Pentavalant)
         • Dopping Process

4. MATERIAL CLASSIFICATION

   • Types of material
     • 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

5. ENERGY BAND

   • Insulator
     • Conduction band – empty
     • Band gap – empty.
     • Electrons are unable to gain enough energy to jump from the valence band to the conduction band.
     • Valence band – filled with electrons.
   • Semiconductor
     • Temperature low – no free electron in the conduction band.
     • Enables some electrons with enough energy to jump from the valence band to the conduction band easily.
     • 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.
   • Conductor
     • Occupied by many conduction electrons, causing metal to become good electric conductor.

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