Conductors, Semi-conductors and Insulators

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  • Conductors, Semiconductor and Insulators
    • Conductors
      • Mostly metals conduct electricity
      • In conductors, there is no space between the conduction and valence bands
        • This allows electrons to move freely through the conduction band allowing them to conduct the electricity
    • Insulators
      • Only non-metals are insulators
      • Insulators have large gaps between the conduction and valence bands
        • This means that the electrons cannot move between the valence and conduction bands, and so cannot conduct electricity
    • Semi-conductors
      • Semi-conductors have small gaps between the conduction and valence bands
        • This means that with a small amount of energy (intrinsic) or as a result of doping (extrinsic)
      • P-type semi-conductors have more holes in the valence band than electrons in the conduction band
        • These occur when a group 4 element is doped with a group three element which has less electrons
          • Then the electrons move between the conduction and valence bands to fill the extra hole and so can conduct electricity
        • P-type semi-conductors always retain an overall neutral charge
      • N-type semi-conductors have more electrons in the conduction band than holes in the valence band
        • These occur when a group four element is doped with a group five element with more electrons
          • This means that the excess electrons are free to move between the conduction and valence band and so can conduct electricity
        • N-type semi-conductors always retain an overall neutral charge

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