Write the difference between an enhancement and depletion type MOSFET.

Q.) Write the difference between an enhancement and depletion type MOSFET.

 Subject: electronic devices and circuits

Enhancement-Type MOSFET:

  • Also known as a Normally-Off MOSFET.
  • Initially, there is no conductive channel between the source and drain terminals.
  • A voltage (gate-source voltage, V gs ) must be applied between the gate and source terminals to create a conductive channel.
  • This voltage causes a depletion region to form under the gate, allowing electrons (for n-channel MOSFETs) or holes (for p-channel MOSFETs) to flow from the source to the drain, creating a conducting path.
  • The amount of current flowing through the channel is controlled by the gate-source voltage.
  • Enhancement-type MOSFETs are commonly used as switches or amplifiers.

Depletion-Type MOSFET:

  • Also known as a Normally-On MOSFET.
  • Initially, a conductive channel exists between the source and drain terminals, even without a gate-source voltage applied.
  • When a negative gate-source voltage (for n-channel MOSFETs) or a positive gate-source voltage (for p-channel MOSFETs) is applied, the depletion region under the gate expands, reducing the width of the conductive channel and, consequently, the current flow.
  • By increasing the gate-source voltage, the depletion region expands further, eventually pinching off the channel and preventing current flow.
  • Depletion-type MOSFETs are less commonly used than enhancement-type MOSFETs due to their lower input impedance and higher susceptibility to noise. However, they can be beneficial in applications requiring a high initial current flow.

Key Differences:

  1. Initial State:

    • Enhancement-Type: Initially, there is no conductive channel, and a gate-source voltage is required to create one.
    • Depletion-Type: Initially, there is a conductive channel, and a gate-source voltage is applied to reduce its width or pinch it off.

  2. Channel Formation:

    • Enhancement-Type: Channel is formed by applying a gate-source voltage, creating a depletion region and allowing carriers to flow.
    • Depletion-Type: Channel exists initially and is depleted by applying a gate-source voltage, reducing the carrier flow.

  3. Applications:

    • Enhancement-Type: Commonly used as switches or amplifiers.
    • Depletion-Type: Less commonly used due to lower input impedance and higher noise susceptibility, but can be beneficial in applications requiring a high initial current flow.