Charge carrier

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In

In conductors

In conducting media, particles serve to carry charge:

• In many
  conduction electrons, and the cloud of free electrons is called a Fermi gas.^[5][6] Many metals have electron and hole bands. In some, the majority carriers are holes.^{[citation needed}
  ]
• In
  ionic solids (see e.g. the Hall–Héroult process for an example of electrolysis of a melted ionic solid). Proton conductors are electrolytic conductors employing positive hydrogen ions as carriers.^[8]
• In a plasma, an electrically charged gas which is found in electric arcs through air, neon signs, and the sun and stars, the electrons and cations of ionized gas act as charge carriers.^[9]
• In a
  cathode ray tube display widely used in televisions and computer monitors until the 2000s.^[11]
• In
  valence-band electron
  population of the semiconductor and are treated as charge carriers because they are mobile, moving from atom site to atom site. In n-type semiconductors, electrons in the conduction band move through the crystal, resulting in an electric current.

When an electron meets with a hole, they recombine and these free carriers effectively vanish.^[13] The energy released can be either thermal, heating up the semiconductor (thermal recombination, one of the sources of waste heat in semiconductors), or released as photons (optical recombination, used in LEDs and semiconductor lasers).^[14] The recombination means an electron which has been excited from the valence band to the conduction band falls back to the empty state in the valence band, known as the holes. The holes are the empty states created in the valence band when an electron gets excited after getting some energy to pass the energy gap.

Majority and minority carriers

The more abundant charge carriers are called majority carriers, which are primarily responsible for

In an intrinsic semiconductor, which does not contain any impurity, the concentrations of both types of carriers are ideally equal. If an intrinsic semiconductor is doped with a donor impurity then the majority carriers are electrons. If the semiconductor is doped with an acceptor impurity then the majority carriers are holes.^[16]

Minority carriers play an important role in

Free carrier concentration is the

• Carrier lifetime
• Free charge
• Molecular diffusion

References