Intrinsic Semiconductors and Extrinsic Semiconductors

• Semiconductors are materials that have electrical conductivity between insulators and conductors.
• Intrinsic semiconductors are pure semiconducting materials, such as silicon (Si) and germanium (Ge).
• Extrinsic semiconductors are doped semiconducting materials, where impurities are deliberately added to alter their electrical properties.

Doping in Semiconductors

Types of Impurities

• Donor impurities: atoms with extra valence electrons. Eg., phosphorus (P) in silicon creates n-type semiconductor.
• Acceptor impurities: atoms with fewer valence electrons. Eg., boron (B) in silicon creates p-type semiconductor.

Doping in Semiconductors

Formation of Extrinsic Semiconductors

• Doping involves adding impurities to semiconductor materials.
• Impurities substitute silicon atoms in silicon crystal lattice.
• Donor impurities create an excess of electrons in the material.
• Acceptor impurities create a deficiency of electrons in the material.

Doping in Semiconductors

n-Type Semiconductors

• In n-type semiconductors, donor impurities provide free electrons.
• Electrons contribute to conductivity by moving within the crystal lattice.
• Majority carriers: Electrons
• Minority carriers: Holes
• Electrons are more mobile than holes due to their negative charge.

Doping in Semiconductors

p-Type Semiconductors

• In p-type semiconductors, acceptor impurities create holes.
• Holes are positive charge carriers, created by the absence of electrons.
• Majority carriers: Holes
• Minority carriers: Electrons
• Holes are more mobile than electrons due to their positive charge.

Doping in Semiconductors

Charge Neutrality

• In a doped semiconductor, the total positive charge equals the total negative charge.
• The number of donor or acceptor impurities equals the number of free electrons or holes, ensuring charge neutrality.
• Charge neutrality is maintained even when electrons and holes combine in the material.

Doping in Semiconductors

Carrier Concentration

• Carrier concentration refers to the abundance of free electrons or holes in a doped semiconductor material.
• It is determined by the dopant concentration and the temperature.
• Higher dopant concentration leads to higher carrier concentration.
• At room temperature, an intrinsic semiconductor has equal concentrations of electrons and holes.

Doping in Semiconductors

Band Diagrams

• Band diagrams show the energy levels of electrons in a semiconductor material.
• The valence band is lower in energy and partially filled with electrons.
• The conduction band is higher in energy and empty in intrinsic semiconductors.
• Doping creates energy levels within the bandgap, called donor or acceptor levels.

Doping in Semiconductors

Energy Levels

• In n-type semiconductors, donor energy levels are closer to the conduction band.
• In p-type semiconductors, acceptor energy levels are closer to the valence band.
• Electrons can be excited from the donor level to the conduction band.
• Holes can be excited from the valence band to the acceptor level.

Doping in Semiconductors

Intrinsic Semiconductors and Extrinsic Semiconductors

• Semiconductors are materials that have electrical conductivity between insulators and conductors.
• Intrinsic semiconductors: pure semiconducting materials (e.g., silicon and germanium).
• Extrinsic semiconductors: doped semiconducting materials with impurities deliberately added.

Doping in Semiconductors

Types of Impurities

• Donor impurities: atoms with extra valence electrons (e.g., phosphorus in silicon creates n-type semiconductor).
• Acceptor impurities: atoms with fewer valence electrons (e.g., boron in silicon creates p-type semiconductor).
• Impurities substitute silicon atoms in the crystal lattice.

Doping in Semiconductors

Formation of Extrinsic Semiconductors

• Impurities are added to semiconductor materials through a process called doping.
• The impurities replace a small fraction of silicon atoms in the crystal lattice.
• Donor impurities create an excess of electrons in the material, leading to n-type semiconductors.
• Acceptor impurities create a deficiency of electrons in the material, leading to p-type semiconductors.

Doping in Semiconductors

n-Type Semiconductors

• In n-type semiconductors, donor impurities donate free electrons.
• Electrons become majority carriers in the material.
• Holes, created by the absence of electrons, are minority carriers.
• Electrons, being negatively charged, are more mobile than holes.

Doping in Semiconductors

p-Type Semiconductors

• In p-type semiconductors, acceptor impurities create holes as majority carriers.
• Electrons, as minority carriers, contribute to conductivity.
• Holes, being positively charged, are more mobile than electrons.

Doping in Semiconductors

Charge Neutrality

• In a doped semiconductor, the total positive charge equals the total negative charge.
• The number of donor or acceptor impurities equals the number of free electrons or holes.
• Charge neutrality is maintained even when free electrons and holes combine in the material.

Doping in Semiconductors

Carrier Concentration

• Carrier concentration refers to the abundance of free electrons or holes in the material.
• It is determined by the concentration of dopant impurities and the temperature.
• Higher dopant concentration leads to higher carrier concentration.
• At room temperature, an intrinsic semiconductor has equal concentrations of electrons and holes.

Doping in Semiconductors

Band Diagrams

• Band diagrams illustrate the energy levels of electrons in a semiconductor material.
• The valence band is lower in energy and partially filled with electrons.
• The conduction band is higher in energy and empty in intrinsic semiconductors.
• Doping introduces energy levels within the bandgap, known as donor or acceptor levels.

Doping in Semiconductors

Energy Levels

• Donor energy levels in n-type semiconductors are closer to the conduction band.
• Acceptor energy levels in p-type semiconductors are closer to the valence band.
• Electrons can be excited from the donor level to the conduction band, contributing to conductivity.
• Holes can be excited from the valence band to the acceptor level, also contributing to conductivity.

Doping in Semiconductors

Examples of Doping

• Example of n-type doping: Phosphorus (P) doping silicon (Si)
  • Phosphorus atom replaces silicon in the crystal lattice.
  • Phosphorus has an extra valence electron, becoming a donor impurity.
  • The extra electron is easily released, creating an excess of free electrons.
• Example of p-type doping: Boron (B) doping silicon (Si)
  • Boron atom replaces silicon in the crystal lattice.
  • Boron has fewer valence electrons, creating a hole as an acceptor impurity.
  • Electrons from adjacent atoms can move into the hole.

Doping in Semiconductors

Equation for Carrier Concentration

• The carrier concentration (n or p) in a doped semiconductor can be calculated using the equation: n = N_d * exp(-E_d / k_B * T)

  p = N_a * exp(-E_a / k_B * T)

  where:

  • N_d and N_a are the donor and acceptor concentrations
  • E_d and E_a are the donor and acceptor levels’ energies
  • k_B is the Boltzmann constant
  • T is the temperature in Kelvin.

Doping in Semiconductors

Applications of Doped Semiconductors

• Doped semiconductors are essential for the operation of many electronic devices, including:
  • Diodes: semiconductor devices that allow current to flow in only one direction.
  • Transistors: amplifying and switching devices used in electronic circuits.
  • Integrated circuits: combinations of transistors, diodes, and other components on a single chip.

Doping in Semiconductors

Summary

• Intrinsic semiconductors are undoped, pure semiconducting materials.
• Extrinsic semiconductors are doped to alter their electrical properties.
• Doping introduces impurities that create either excess free electrons (n-type) or holes (p-type).
• Doped semiconductors are used in various electronic devices, such as diodes and transistors.

Doping in Semiconductors - Intrinsic semiconductors and extrinsic semiconductors

• Semiconductors are materials that have electrical conductivity between insulators and conductors.
• Intrinsic semiconductors are pure semiconducting materials, such as silicon (Si) and germanium (Ge).
• Extrinsic semiconductors are doped semiconducting materials, where impurities are deliberately added to alter their electrical properties.

Types of Impurities

• Donor impurities: atoms with extra valence electrons. Eg., phosphorus (P) in silicon creates n-type semiconductor.
• Acceptor impurities: atoms with fewer valence electrons. Eg., boron (B) in silicon creates p-type semiconductor.
• Impurities substitute silicon atoms in silicon crystal lattice.

Formation of Extrinsic Semiconductors

• Doping involves adding impurities to semiconductor materials.
• Impurities substitute silicon atoms in the crystal lattice.
• Donor impurities create an excess of electrons in the material.
• Acceptor impurities create a deficiency of electrons in the material.

n-Type Semiconductors

• In n-type semiconductors, donor impurities provide free electrons.
• Electrons contribute to conductivity by moving within the crystal lattice.
• Majority carriers: Electrons
• Minority carriers: Holes
• Electrons are more mobile than holes due to their negative charge.

p-Type Semiconductors

• In p-type semiconductors, acceptor impurities create holes.
• Holes are positive charge carriers, created by the absence of electrons.
• Majority carriers: Holes
• Minority carriers: Electrons
• Holes are more mobile than electrons due to their positive charge.

Charge Neutrality

• In a doped semiconductor, the total positive charge equals the total negative charge.
• The number of donor or acceptor impurities equals the number of free electrons or holes, ensuring charge neutrality.
• Charge neutrality is maintained even when electrons and holes combine in the material.

Carrier Concentration

• Carrier concentration refers to the abundance of free electrons or holes in a doped semiconductor material.
• It is determined by the dopant concentration and the temperature.
• Higher dopant concentration leads to higher carrier concentration.
• At room temperature, an intrinsic semiconductor has equal concentrations of electrons and holes.

Band Diagrams

• Band diagrams show the energy levels of electrons in a semiconductor material.
• The valence band is lower in energy and partially filled with electrons.
• The conduction band is higher in energy and empty in intrinsic semiconductors.
• Doping creates energy levels within the bandgap, called donor or acceptor levels.

Energy Levels

• In n-type semiconductors, donor energy levels are closer to the conduction band.
• In p-type semiconductors, acceptor energy levels are closer to the valence band.
• Electrons can be excited from the donor level to the conduction band.
• Holes can be excited from the valence band to the acceptor level.

Examples of Doping

• Example of n-type doping: Phosphorus (P) doping silicon (Si)
  • Phosphorus atom replaces silicon in the crystal lattice.
  • Phosphorus has an extra valence electron, becoming a donor impurity.
  • The extra electron is easily released, creating an excess of free electrons.
• Example of p-type doping: Boron (B) doping silicon (Si)
  • Boron atom replaces silicon in the crystal lattice.
  • Boron has fewer valence electrons, creating a hole as an acceptor impurity.
  • Electrons from adjacent atoms can move into the hole.

Equation for Carrier Concentration

• The carrier concentration (n or p) in a doped semiconductor can be calculated using the equation: n = N_d * exp(-E_d / k_B * T)

  p = N_a * exp(-E_a / k_B * T)

  where:

  • N_d and N_a are the donor and acceptor concentrations
  • E_d and E_a are the donor and acceptor levels’ energies
  • k_B is the Boltzmann constant
  • T is the temperature in Kelvin.

Applications of Doped Semiconductors

• Doped semiconductors are essential for the operation of many electronic devices, including:
  • Diodes: semiconductor devices that allow current to flow in only one direction.
  • Transistors: amplifying and switching devices used in electronic circuits.
  • Integrated circuits: combinations of transistors, diodes, and other components on a single chip.

Summary

• Intrinsic semiconductors are undoped, pure semiconducting materials.
• Extrinsic semiconductors are doped to alter their electrical properties.
• Doping introduces impurities that create either excess free electrons (n-type) or holes (p-type).
• Doped semiconductors are used in various electronic devices, such as diodes and transistors.