Pn Junction Diode: Depletion Region

Depletion Region in Pn Junction

Formation of Depletion Region

• The depletion region is a region in a Pn junction where the concentration of charge carriers is depleted.
• It is formed when a p-type semiconductor and an n-type semiconductor are brought together.
• The p-type semiconductor has an excess of holes (positive charge carriers), while the n-type semiconductor has an excess of electrons (negative charge carriers).
• At the junction, the electrons from the n-type semiconductor flow into the p-type semiconductor, filling some of the holes.
• Similarly, the holes from the p-type semiconductor flow into the n-type semiconductor, filling some of the electrons.
• This process is known as diffusion.

Characteristics of Depletion Region

• The depletion region is a region of high resistance due to the lack of charge carriers.
• It is also known as the space charge region or the depletion layer.
• The width of the depletion region depends on the concentration of charge carriers in the p-type and n-type semiconductors.
• The depletion region acts as a barrier to the flow of charge carriers across the junction.

Depletion Region Width

• The width of the depletion region can be calculated using the following formula:

W = √(2ε(Vbi - V)/q * (Na + Nd) / (Na * Nd))

• Where:
  • W is the width of the depletion region
  • ε is the permittivity of the semiconductor material
  • Vbi is the built-in voltage
  • V is the applied voltage
  • q is the charge of an electron
  • Na is the concentration of acceptors in the p-type semiconductor
  • Nd is the concentration of donors in the n-type semiconductor

Importance of Depletion Region

• The depletion region plays a crucial role in the operation of Pn junction diodes.
• It allows the diode to control the flow of current across the junction.
• The depletion region can be manipulated by applying an external voltage to the diode, allowing it to be used as a rectifier, switch, or amplifier.