9.2 Doping and charge carriers

Semiconductors are the backbone of modern electronics. Doping, a process of adding impurities, transforms these materials into powerful conductors. By introducing donor or acceptor atoms, we create n-type and p-type semiconductors with unique electrical properties.

Understanding charge carriers is crucial in semiconductor physics. Electrons and holes, the negative and positive charge carriers, determine how current flows through these materials. The balance of majority and minority carriers shapes the behavior of semiconductor devices.

Doping and Semiconductor Types

Doping Process and Effects

Top images from around the web for Doping Process and Effects

• 

  Doping: Connectivity of Semiconductors | Introduction to Chemistry View original

  Is this image relevant?

• 

  Doping: Connectivity of Semiconductors | Introduction to Chemistry View original

  Is this image relevant?

• 

  Doping: Connectivity of Semiconductors | Introduction to Chemistry View original

  Is this image relevant?

• 

  Doping: Connectivity of Semiconductors | Introduction to Chemistry View original

  Is this image relevant?

• 

  Doping: Connectivity of Semiconductors | Introduction to Chemistry View original

  Is this image relevant?

1 of 3

Top images from around the web for Doping Process and Effects

• 

  Doping: Connectivity of Semiconductors | Introduction to Chemistry View original

  Is this image relevant?

• 

  Doping: Connectivity of Semiconductors | Introduction to Chemistry View original

  Is this image relevant?

• 

  Doping: Connectivity of Semiconductors | Introduction to Chemistry View original

  Is this image relevant?

• 

  Doping: Connectivity of Semiconductors | Introduction to Chemistry View original

  Is this image relevant?

• 

  Doping: Connectivity of Semiconductors | Introduction to Chemistry View original

  Is this image relevant?

1 of 3

• Doping introduces impurities into intrinsic semiconductors to alter their electrical properties
• Involves adding small amounts of dopant atoms with different numbers of valence electrons compared to the host semiconductor material
• Dopant atoms replace some of the host atoms in the crystal lattice
• Doping creates additional energy levels within the bandgap near the conduction band (for n-type) or valence band (for p-type)
• Doping increases the conductivity of the semiconductor by several orders of magnitude

N-type Semiconductors and Donors

• N-type semiconductors are created by doping with donor impurities (pentavalent atoms like phosphorus or arsenic)
• Donor atoms have five valence electrons, one more than the host semiconductor atoms (typically silicon or germanium)
• Four valence electrons form covalent bonds with neighboring semiconductor atoms, while the fifth electron is loosely bound
• The loosely bound electron can be easily excited into the conduction band, becoming a free electron
• Donor energy level is created just below the conduction band, facilitating electron excitation
• Examples of n-type semiconductors include phosphorus-doped silicon and arsenic-doped germanium

P-type Semiconductors and Acceptors

• P-type semiconductors are created by doping with acceptor impurities (trivalent atoms like boron or gallium)
• Acceptor atoms have three valence electrons, one fewer than the host semiconductor atoms
• The missing electron creates a hole in the valence band, which can accept an electron from a neighboring atom
• Holes act as positive charge carriers and can move through the crystal lattice
• Acceptor energy level is created just above the valence band, facilitating hole formation
• Examples of p-type semiconductors include boron-doped silicon and gallium-doped germanium

Charge Carriers

Electrons and Holes

• Electrons are negative charge carriers in semiconductors
• In intrinsic semiconductors, electrons are excited from the valence band to the conduction band by thermal energy or light
• In n-type semiconductors, electrons are the majority charge carriers due to the presence of donor atoms
• Holes are positive charge carriers in semiconductors
• Holes are created when electrons leave their positions in the valence band
• In p-type semiconductors, holes are the majority charge carriers due to the presence of acceptor atoms

Majority and Minority Carriers

• Majority carriers are the type of charge carriers that are most abundant in a semiconductor
• In n-type semiconductors, electrons are the majority carriers, while holes are the minority carriers
• In p-type semiconductors, holes are the majority carriers, while electrons are the minority carriers
• The concentration of majority carriers is much higher than that of minority carriers
• The type and concentration of majority carriers determine the electrical properties of the semiconductor
• Examples: In phosphorus-doped silicon (n-type), electrons are the majority carriers, and in boron-doped silicon (p-type), holes are the majority carriers

Energy Levels

Fermi Level and its Significance

• The Fermi level is a hypothetical energy level representing the highest occupied energy state at absolute zero temperature
• In intrinsic semiconductors, the Fermi level lies approximately in the middle of the bandgap
• Doping shifts the Fermi level towards the conduction band (for n-type) or valence band (for p-type)
• The position of the Fermi level relative to the conduction and valence bands determines the concentration of electrons and holes
• The Fermi level is important for understanding the behavior of semiconductors in electronic devices
• The difference in Fermi levels between two differently doped semiconductors creates a built-in potential when they are brought into contact (e.g., in a p-n junction)
• The Fermi level is a key concept in semiconductor physics and device engineering