JFET Clarification: Why the Depletion Region is Wider near the Top?

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In summary, the depletion region in a n channel JFET is wider near the top of both p-type materials due to the difference in voltage between the source and drain. This is not the case for BJT because the voltage across the depletion region remains constant, regardless of the bias at the terminals.
  • #1
Physicslearner500039
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Hi All,

I have read this following statement about n channel JFET that depletion region is wider near the top of both p - type materials. what is the exact reason for this? and why such description is not provided for BJT, because even in BJT we have P-N junction?

Thanks in advance,

Regards,
Satya
 
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  • #2
For any JFET the depletion region is always even until and unless the source voltage is different from the drain voltage. When there is a voltage b/w source and drain, Vgs is different from Vgd and the width of the depletion layer depends on Vgs or Vgd.

In BJT the voltage across the depletion region does not vary regionally regardless of the bias at the terminals.
 

Related to JFET Clarification: Why the Depletion Region is Wider near the Top?

1. Why is the depletion region wider near the top of a JFET?

The depletion region is the region in a JFET where there are no free charge carriers due to the presence of a reverse-bias voltage. The width of this region is determined by the strength of the reverse-bias voltage and the doping concentrations of the semiconductor material. Near the top of the JFET, the reverse-bias voltage is at its highest, resulting in a wider depletion region.

2. How does the width of the depletion region affect the performance of a JFET?

The width of the depletion region plays a crucial role in the operation of a JFET. A wider depletion region means a larger portion of the channel is blocked, leading to a decrease in the flow of current. This allows the JFET to act as a voltage-controlled resistor, as the width of the depletion region can be varied by changing the applied voltage.

3. Can the depletion region be affected by external factors?

Yes, the width of the depletion region can be affected by external factors such as temperature and impurities in the semiconductor material. An increase in temperature can result in a wider depletion region, while impurities can affect the doping concentrations and alter the width of the depletion region.

4. How does the width of the depletion region change with increasing reverse-bias voltage?

As the reverse-bias voltage increases, the width of the depletion region also increases. This is due to the stronger electric field created by the higher voltage, which pushes the depletion region further into the channel. However, at a certain point, called the pinch-off voltage, the depletion region reaches its maximum width and any further increase in reverse-bias voltage will not affect it.

5. How does the width of the depletion region vary between different types of JFETs?

The width of the depletion region can vary between different types of JFETs, depending on their design and fabrication process. For example, in a junction-gate JFET, the depletion region is wider near the p-n junction due to the presence of a gate electrode. On the other hand, in a metal-oxide-semiconductor JFET, the depletion region is wider near the metal gate due to the presence of an insulating layer between the gate and the channel.

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