Electronics Engineering (ELEX) Board Practice Exam

How can the threshold voltage of an n-channel MOSFET be increased?

1. By increasing the channel dopant concentration

2. By reducing the channel dopant concentration

3. By increasing the gate voltage

4. By decreasing the gate voltage

The correct answer is: By reducing the channel dopant concentration

The threshold voltage of an n-channel MOSFET can be increased by reducing the channel dopant concentration. In a MOSFET, the threshold voltage is influenced by the amount of n-type dopant present in the channel region. By reducing the concentration of this dopant, fewer charges are available to enhance the conduction in the channel, which means that a higher gate voltage is needed to create the necessary electric field to form a conductive channel between the source and drain terminals. This is due to the relationship between the dopant concentration and the electric field that develops when a gate voltage is applied. A lower dopant concentration raises the potential barrier that must be overcome to invert the channel from p-type to n-type under the gate, resulting in a higher threshold voltage. This principle is used in device engineering to tailor the performance of MOSFETs for specific applications.