13.1.1 Understanding intrinsic and extrinsic semiconductors

• What are intrinsic semiconductors made of?

  Pure materials
• Give an example of an intrinsic semiconductor.

  Pure silicon
• Steps of thermal excitation in intrinsic semiconductors

  1️⃣ Electron gains energy

  2️⃣ Electron moves from valence band to conduction band

  3️⃣ Electron becomes a free charge carrier
• Intrinsic semiconductors have high electrical conductivity at room temperature.

  False
• Thermal excitation in intrinsic semiconductors allows electrons to move from the conduction band to the valence band.

  False
• What is the process called that enhances the electrical conductivity of semiconductors by adding impurities?

  Doping
• Phosphorus is commonly used as a dopant in n-type semiconductors.


  True
• The increased concentration of electrons in n-type semiconductors leads to higher electrical conductivity
• What is the typical band gap of intrinsic semiconductors in eV?

  Around 1 eV
• N-type semiconductors are doped with impurities that have more valence electrons than the host material.
• N-type semiconductors are doped with elements that have fewer valence electrons than the host material.

  False
• P-type semiconductors are created by doping intrinsic semiconductors with impurities that have more valence electrons.

  False
• Holes are the majority charge carriers in n-type semiconductors.

  False
• Intrinsic semiconductors have high electrical conductivity at room temperature.

  False
• Intrinsic semiconductors have a valence band filled with electrons and a conduction band that is mostly empty
• The valence band and conduction band in intrinsic semiconductors are separated by an energy gap called the band gap
• Order the materials based on their band gap size from largest to smallest:

  1️⃣ Insulator

  2️⃣ Semiconductor

  3️⃣ Conductor
• The electrical conductivity of intrinsic semiconductors can be increased by introducing impurities
• In n-type semiconductors, free electrons are the majority charge carriers.


  True
• What are common dopants used to create p-type semiconductors?

  Boron, gallium
• In p-type semiconductors, impurities introduce holes
• Intrinsic semiconductors have no impurities added.


  True
• The valence band and conduction band in intrinsic semiconductors are separated by a(n) gap
• Why is the electrical conductivity of intrinsic semiconductors limited at room temperature?

  Small number of charge carriers
• What is the role of the band gap in intrinsic semiconductors?

  Separates valence and conduction bands
• Match the material with its electrical conductivity property:

  Insulator ↔️ Very Low

  Intrinsic Semiconductor ↔️ Low

  Conductor ↔️ High
• What type of impurity is added to create p-type semiconductors?

  Elements with fewer valence electrons
• Extrinsic semiconductors are intrinsic semiconductors that have had impurities added through a process called doping
• Common dopants for n-type semiconductors include phosphorus and arsenic
• In intrinsic semiconductors, the valence band and conduction band are separated by an energy gap known as the band gap
• Match the type of extrinsic semiconductor with its majority carriers:

  N-type ↔️ Electrons

  P-type ↔️ Holes
• Common dopants used to create n-type semiconductors include phosphorus and arsenic
• The increased concentration of electrons in n-type semiconductors results in higher electrical conductivity
• Match the semiconductor type with its doping and majority carriers:

  P-type ↔️ Fewer valence electrons, Holes

  N-type ↔️ More valence electrons, Electrons
• What is an intrinsic semiconductor?

  Pure semiconductor
• The band gap in semiconductors is larger than in insulators.

  False
• What are the two bands present in the energy band structure of intrinsic semiconductors?

  Valence band, conduction band
• Match the material type with its band gap size:

  Insulator ↔️ Large (>3 eV)

  Semiconductor ↔️ Small (1-3 eV)

  Conductor ↔️ None
• Insulators have very low electrical conductivity.


  True
• N-type semiconductors are doped with elements that have more valence electrons.


  True