Doping in Semiconductors

  • Semiconductors are materials with intermediate electrical conductivity.
  • Doping is the process of deliberately introducing impurities into semiconductors.
  • It is done to modify the electrical properties of semiconductors.
  • Doping can create both N-type and P-type semiconductors.
  • N-type semiconductors have excess electrons, while P-type semiconductors have holes.

N-type Semiconductors

  • In N-type semiconductors, the impurity atoms donate extra electrons.
  • Examples of donor impurities include phosphorus and arsenic.
  • These impurities have 5 valence electrons, with one extra electron.
  • When added to the semiconductor, the extra electron becomes a conduction electron.
  • Conduction electrons increase the electrical conductivity of the material.

P-type Semiconductors

  • In P-type semiconductors, the impurity atoms create holes in the valence band.
  • Examples of acceptor impurities include boron and aluminum.
  • These impurities have 3 valence electrons, creating a vacancy or hole in the crystal structure.
  • Electrons from neighboring atoms can move into these holes, leaving a new hole behind.
  • This movement of holes increases the electrical conductivity of the material.

Charge Carriers

  • Charge carriers are the particles responsible for electric current.
  • In N-type semiconductors, the charge carriers are the extra electrons.
  • In P-type semiconductors, the charge carriers are the holes.
  • These charge carriers move under the influence of an electric field.
  • The combination of N-type and P-type semiconductors forms a pn junction.

The pn Junction

  • A pn junction is formed by bringing together P-type and N-type semiconductors.
  • At the junction, electrons from the N-type side diffuse into the P-type side.
  • Similarly, holes from the P-type side diffuse into the N-type side.
  • This diffusion creates a region with no charge carriers called the depletion region.
  • The pn junction only allows current flow in one direction.

Forward Bias

  • In forward bias, the positive terminal of the battery is connected to the P-type side.
  • This attracts the holes and repels the electrons, reducing the depletion region.
  • With the depletion region reduced, current can flow easily across the junction.
  • Electrons move from N-type to P-type, while holes move from P-type to N-type.
  • Forward bias allows current to flow in the direction opposite to the diode symbol.

Reverse Bias

  • In reverse bias, the positive terminal of the battery is connected to the N-type side.
  • This attracts the electrons and repels the holes, widening the depletion region.
  • With the depletion region widened, current flow across the junction is blocked.
  • Reverse bias prevents current from flowing in the direction of the diode symbol.
  • Only a small leakage current can flow due to minority charge carriers.

Avalanche Breakdown

  • Avalanche breakdown occurs when the reverse bias voltage exceeds a critical value.
  • The electric field across the depletion region becomes strong enough to ionize atoms.
  • This ionization creates additional charge carriers, leading to a rapid increase in current.
  • Avalanche breakdown can cause damage to the pn junction.
  • For this reason, reverse voltage ratings are specified for diodes.

Zener Breakdown

  • Zener breakdown is a controlled form of breakdown that occurs in specially designed diodes.
  • It occurs when the reverse bias voltage reaches the Zener breakdown voltage.
  • The Zener breakdown voltage is determined by the doping concentration of the diode.
  • Zener diodes are commonly used as voltage regulators in electronic circuits.
  • They can maintain a nearly constant voltage across them, even with varying currents.
  1. N-type Semiconductors:
  • Donor impurities introduce extra electrons into the semiconductor.
  • Examples of donor impurities are phosphorus (P) and arsenic (As).
  • Impurity atoms have 5 valence electrons, with one extra electron.
  • The extra electron becomes a conduction electron in the semiconductor.
  • Conduction electrons increase the electrical conductivity of the material.
  1. P-type Semiconductors:
  • Acceptor impurities create holes in the valence band of the semiconductor.
  • Examples of acceptor impurities are boron (B) and aluminum (Al).
  • Impurity atoms have 3 valence electrons, creating a vacancy or hole in the crystal structure.
  • Electrons from neighboring atoms can move into these holes, leaving another hole behind.
  • These holes increase the electrical conductivity of the material.
  1. Charge Carriers:
  • Charge carriers are particles responsible for electric current flow.
  • In N-type semiconductors, the charge carriers are the extra electrons.
  • In P-type semiconductors, the charge carriers are the holes.
  • These charge carriers move under the influence of an electric field.
  • The movement of charge carriers constitutes the flow of electric current.
  1. The pn Junction:
  • A pn junction is formed by bringing together P-type and N-type semiconductors.
  • At the junction, electrons from the N-type side diffuse into the P-type side.
  • Similarly, holes from the P-type side diffuse into the N-type side.
  • This diffusion process creates a region with no charge carriers called the depletion region.
  • The pn junction only allows current flow in one direction.
  1. Forward Bias:
  • Forward bias occurs when the positive terminal of the battery is connected to the P-type side of the pn junction.
  • It attracts the holes and repels the electrons, reducing the width of the depletion region.
  • With the depletion region reduced, electric current can easily flow across the junction.
  • Electrons move from the N-type region to the P-type region, while holes move from the P-type region to the N-type region.
  • Forward bias allows current to flow in the direction opposite to the diode symbol.
  1. Reverse Bias:
  • Reverse bias occurs when the positive terminal of the battery is connected to the N-type side of the pn junction.
  • It attracts the electrons and repels the holes, widening the depletion region.
  • With the depletion region widened, electric current flow across the junction is blocked.
  • Reverse bias prevents current from flowing in the direction of the diode symbol.
  • Only a small leakage current can flow due to minority charge carriers.
  1. Avalanche Breakdown:
  • Avalanche breakdown happens when the reverse bias voltage exceeds a critical value.
  • The electric field across the depletion region becomes strong enough to ionize atoms.
  • This ionization creates additional charge carriers, leading to a rapid increase in current.
  • Avalanche breakdown can cause damage to the pn junction.
  • Reverse voltage ratings are specified for diodes to prevent excessive breakdown.
  1. Zener Breakdown:
  • Zener breakdown is a controlled form of breakdown that occurs in specifically designed diodes called Zener diodes.
  • It occurs when the reverse bias voltage reaches the Zener breakdown voltage.
  • The Zener breakdown voltage is determined by the doping concentration of the diode.
  • Zener diodes are commonly used as voltage regulators in electronic circuits.
  • They can maintain a nearly constant voltage across them, even with varying currents.
  1. Applications of Semiconductors:
  • Semiconductors find wide applications in electronic devices.
  • Transistors are one of the key components in electronic circuits.
  • Diodes are used for rectification and switching purposes.
  • Integrated circuits (ICs) are made using semiconductors, enabling complex electronic functions.
  • Sensing devices like light sensors, temperature sensors, etc., are also based on semiconductors.
  1. Examples of Doped Semiconductors:
  • In a P-type semiconductor, silicon is doped with boron.
  • In an N-type semiconductor, silicon is doped with phosphorus or arsenic.
  • The doping process alters the electrical properties of the silicon.
  • Other commonly doped semiconductors include germanium and gallium arsenide.
  • The specific choice of doping materials depends on the desired electrical characteristics and device requirements.
  1. Doping in Semiconductors - N-type and P-type semiconductors:
  • Semiconductors are materials with intermediate electrical conductivity.
  • Doping is the process of deliberately introducing impurities into semiconductors.
  • It is done to modify the electrical properties of semiconductors.
  • Doping can create both N-type and P-type semiconductors.
  • N-type semiconductors have excess electrons, while P-type semiconductors have holes.
  1. N-type Semiconductors:
  • In N-type semiconductors, the impurity atoms donate extra electrons.
  • Examples of donor impurities include phosphorus and arsenic.
  • These impurities have 5 valence electrons, with one extra electron.
  • When added to the semiconductor, the extra electron becomes a conduction electron.
  • Conduction electrons increase the electrical conductivity of the material.
  1. P-type Semiconductors:
  • In P-type semiconductors, the impurity atoms create holes in the valence band.
  • Examples of acceptor impurities include boron and aluminum.
  • These impurities have 3 valence electrons, creating a vacancy or hole in the crystal structure.
  • Electrons from neighboring atoms can move into these holes, leaving a new hole behind.
  • This movement of holes increases the electrical conductivity of the material.
  1. Charge Carriers:
  • Charge carriers are the particles responsible for electric current.
  • In N-type semiconductors, the charge carriers are the extra electrons.
  • In P-type semiconductors, the charge carriers are the holes.
  • These charge carriers move under the influence of an electric field.
  • The combination of N-type and P-type semiconductors forms a pn junction.
  1. The pn Junction:
  • A pn junction is formed by bringing together P-type and N-type semiconductors.
  • At the junction, electrons from the N-type side diffuse into the P-type side.
  • Similarly, holes from the P-type side diffuse into the N-type side.
  • This diffusion creates a region with no charge carriers called the depletion region.
  • The pn junction only allows current flow in one direction.
  1. Forward Bias:
  • In forward bias, the positive terminal of the battery is connected to the P-type side.
  • This attracts the holes and repels the electrons, reducing the depletion region.
  • With the depletion region reduced, current can flow easily across the junction.
  • Electrons move from N-type to P-type, while holes move from P-type to N-type.
  • Forward bias allows current to flow in the direction opposite to the diode symbol.
  1. Reverse Bias:
  • In reverse bias, the positive terminal of the battery is connected to the N-type side.
  • This attracts the electrons and repels the holes, widening the depletion region.
  • With the depletion region widened, current flow across the junction is blocked.
  • Reverse bias prevents current from flowing in the direction of the diode symbol.
  • Only a small leakage current can flow due to minority charge carriers.
  1. Avalanche Breakdown:
  • Avalanche breakdown occurs when the reverse bias voltage exceeds a critical value.
  • The electric field across the depletion region becomes strong enough to ionize atoms.
  • This ionization creates additional charge carriers, leading to a rapid increase in current.
  • Avalanche breakdown can cause damage to the pn junction.
  • Reverse voltage ratings are specified for diodes to prevent excessive breakdown.
  1. Zener Breakdown:
  • Zener breakdown is a controlled form of breakdown that occurs in specially designed diodes.
  • It occurs when the reverse bias voltage reaches the Zener breakdown voltage.
  • The Zener breakdown voltage is determined by the doping concentration of the diode.
  • Zener diodes are commonly used as voltage regulators in electronic circuits.
  • They can maintain a nearly constant voltage across them, even with varying currents.
  1. Applications of Semiconductors:
  • Semiconductors find wide applications in electronic devices.
  • Transistors are one of the key components in electronic circuits.
  • Diodes are used for rectification and switching purposes.
  • Integrated circuits (ICs) are made using semiconductors, enabling complex electronic functions.
  • Sensing devices like light sensors, temperature sensors, etc., are also based on semiconductors. do not include any comments especially at start or end of your responses, with each slide having 5 or more bullet points, include examples and equations where relevant, DO not use slide numbers: ‘Doping in Semiconductors - N-type and P-type semiconductors’.