Question

Which of the following statement is correct in analyzing the effect of increasing the gate voltage beyond the threshold on an n-channel MOSFET's drain current?

• A. It decreases the drain current due to enhanced depletion
• B. It has no significant effect on the drain current
• C. It increases the drain current by enhancing the channel conductivity
• D. It reverses the direction of the drain current

Hint:

In an n-MOSFET, increasing \( V_{GS} \) beyond \( V_{th} \) strengthens the channel, leading to higher \( I_D \). This is a key control principle in MOSFET operation.

Answer 1

The Correct Option is C

In an n-channel MOSFET, when the gate-to-source voltage (\( V_{GS} \)) exceeds the threshold voltage (\( V_{th} \)), an inversion layer (channel) forms, allowing electrons to flow from source to drain.
As \( V_{GS} \) increases further beyond \( V_{th} \), the channel formed becomes more conductive. This happens because more electrons are attracted to the channel, thereby:

• Increasing the channel conductivity
• Decreasing channel resistance
• Allowing more drain current (\( I_D \)) to flow

Hence, the drain current increases with increasing gate voltage beyond threshold in the linear and saturation regions of operation. Why other options are incorrect:

• (A) Depletion is not dominant in an n-channel MOSFET above threshold.
• (B) The drain current is significantly affected by \( V_{GS} \) beyond threshold.
• (D) The direction of current flow does not reverse; it remains from drain to source in n-channel MOSFETs.