13.1.2 Exploring p-n junctions

• A p-type semiconductor is doped with trivalent impurities.
• What type of charge carriers are dominant in an n-type semiconductor?

  Free electrons
• What is the main charge carrier in an n-type semiconductor?

  Electrons
• What is the depletion region in a p-n junction depleted of?

  Free charge carriers
• The built-in potential at a p-n junction establishes an equilibrium state.
• What type of impurities are used to create electron holes in a p-type semiconductor?

  Trivalent
• Match the property with the correct semiconductor type:

  Trivalent dopant ↔️ p-type

  Pentavalent dopant ↔️ n-type
• The depletion region in a p-n junction forms a built-in potential.
• When p-type and n-type semiconductors are brought together, the free electrons in the n-type region diffuse into the p-type region, and the electron holes in the p-type region diffuse into the n-type region. This process is called diffusion
• What is the built-in potential in a p-n junction?

  Electric potential across depletion region
• A p-type semiconductor has excess free electrons.

  False
• Steps in the formation of a p-n junction

  1️⃣ Diffusion of free electrons and holes

  2️⃣ Formation of the depletion region

  3️⃣ Creation of built-in potential
• The p-n junction is formed when a p-type semiconductor is brought into contact with an n-type
• The diffusion current in a p-n junction is caused by a concentration gradient
• Steps in the formation of the depletion region at a p-n junction

  1️⃣ Free electrons in the n-type region diffuse into the p-type region

  2️⃣ Electron holes in the p-type region diffuse into the n-type region

  3️⃣ Electrons and holes recombine, leaving behind immobile ions

  4️⃣ A built-in potential forms across the depletion region
• What is the role of the built-in potential in a p-n junction?

  Prevents further diffusion
• Which current is dominant under forward bias in a p-n junction?

  Diffusion current
• Under forward bias, the depletion region width decreases.


  True
• Under reverse bias, the built-in potential at a p-n junction is increased
• Under reverse bias, the overall current flow is dominated by the drift current.
• A p-type semiconductor has electron holes as its primary charge carriers.
• In the formation of a p-n junction, free electrons in the n-type region diffuse into the p-type region.
• The built-in potential acts as a barrier to further diffusion of charge carriers.

  True
• The depletion region is the area at the p-n junction where there are no free charge carriers
• Match the current type with its cause:

  Diffusion Current ↔️ Concentration gradient

  Drift Current ↔️ Electric field
• The built-in potential acts as a barrier to further diffusion of charge carriers.

  True
• Under forward bias, the drift current is minimal because it is not supported by the applied voltage.


  True
• Under forward bias, the current flow across the junction is increased
• Under reverse bias, the depletion region widens and the built-in potential increases.
• The I-V characteristic of a p-n junction shows a low resistance under forward bias and a high resistance under reverse bias.
• What type of charge carriers are dominant in a p-type semiconductor?

  Electron holes
• A p-type semiconductor uses trivalent impurities like Boron, while an n-type semiconductor uses pentavalent impurities like Phosphorus.


  True
• Steps in the formation of a p-n junction

  1️⃣ Diffusion of charge carriers

  2️⃣ Recombination of charge carriers

  3️⃣ Formation of the depletion region

  4️⃣ Drift current opposes diffusion

  5️⃣ Equilibrium state is established
• Match the type of current with its cause and direction:

  Diffusion Current ↔️ Concentration gradient, higher to lower concentration

  Drift Current ↔️ Electric field, opposite to field direction
• What are two common semiconductor devices that rely on the p-n junction?

  Diodes and transistors
• N-type semiconductors are doped with pentavalent impurities to produce excess free electrons.
• Holes are the main charge carriers in p-type semiconductors, while electrons are the main charge carriers in n-type semiconductors.

  True
• Steps in the formation of the depletion region

  1️⃣ Diffusion of free electrons and holes

  2️⃣ Recombination of charge carriers

  3️⃣ Depletion region forms with no free carriers

  4️⃣ Built-in potential establishes equilibrium
• Steps in the formation of the depletion region

  1️⃣ Diffusion of electrons and holes

  2️⃣ Recombination of charge carriers

  3️⃣ Creation of immobile charged ions

  4️⃣ Formation of built-in potential
• The built-in potential is determined by the doping concentrations in the p-type and n-type regions