Semiconductor

• Materials that can function as a conductor or insulator depending on the flow of current are called semiconductors

  
• Semiconductors, like Silicon (Si), are made up of individual atoms bonded together in a regular, periodic structure where each atom is surrounded by 8 electrons
• Characteristics of conductors, semiconductors, and insulators:

  • Conductors allow the flow of charge when applied with a voltage
  • Semiconductors have conductivity between conductors and insulators
  • Insulators do not allow the flow of current
• Temperature dependence:

  • Resistance of a conductor increases with temperature
  • Resistance of a semiconductor decreases with temperature, acting as an insulator at absolute zero
  • Insulators have very high resistance that decreases with temperature
• Conductivity:

  • Conductors have very high conductivity
  • Semiconductors have intermediate conductivity, acting as insulator & conductor at different conditions
  • Insulators have very low conductivity
• Conduction:

  • Conduction in conductors is due to free electrons in metal bonding
  • Conduction in semiconductors is due to the movement of electrons & holes
  • Insulators have no free electrons or holes, thus no conduction
• Band gap:

  • Conductors have no or low energy gap between the conduction & valence band
  • Semiconductors have a band gap greater than conductors but smaller than insulators
  • Insulators have a huge band gap, needing an enormous amount of energy for conduction
• Resistivity:

  • Conductors have low resistivity
  • Semiconductors have normal resistivity
  • Insulators have very high resistivity
• Absolute zero:

  • Some special conductors turn into superconductors when supercooled to absolute zero
  • Semiconductors turn into insulators at absolute zero
  • Insulators' resistance increases at absolute zero
• Valence electrons in outer shell:

  • Conductors have 1 valence electron
  • Semiconductors have 4 valence electrons
  • Insulators have 8 valence electrons
• Applications:

  • Conductors like iron & copper are made into wires for carrying electric current
  • Semiconductors are used in electronic devices like cellphones & computers
  • Insulators are used for protection against high voltages & preventing electrical shorts