What is the purpose of the depletion region in P-N junction semiconductors?

In summary, the conversation discusses the concept of biasing in semiconductors, specifically focusing on the depletion region in forward biasing. It is explained that in forward biasing, the width of the depletion region is reduced due to the decrease in potential barrier at the junction. However, the idea of drift current causing the depletion region to widen is clarified to be incorrect, as drift current is only a small amount of current that flows due to an electric field and does not affect the depletion region. The concept of diffusion current and its role in the depletion region is also discussed. The conversation ends with a clarification that the depletion region acts as a barrier to the drift current, allowing only diffusion current to flow.
  • #1
Praveen1901
2
0
I'm new to semiconductors.

While I was studying types of biasing in semiconductors, here's what I read -
'In forward biasing, the width of the depletion region is reduced.'

Here's what I thought -
Since the potential barrier is reduced in the junction due to external potential, the diffusion Current directed from p to n side should increases, leaving behind more -ve charge on P side and more +ve charge on the n side, and thus increasing the depletion region.

Please correct me where I'm wrong :)
 
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  • #2
First, by saying semiconductor, I think you really mean PN junction diode.
Now, drift current is the tiny amount of current that flows when hole/electrons move from where they are highly concentrated to a region of lower concentration. This doesn't say anything about due to application of electric field. Any current that flows due to electric field is drift current. Now you may say that this drift current may however still cause the depletion layer to widen. No, it won't.
You can consider it this way, if I have such a PN Junction diode and I forward biase it, the little electrons at the P region will get attracted to the positive terminal of the battery/power source. But immediately, this electrons will be replaced by other electrons from the N region since there are no more electrons in P to prevent such crossing over (remember the electrons at the P region was formerly preventing more electrons from crossing, which is what creates the layer in the first place).This is still a diffusion current. This crossing over would have kept the barrier independent of voltage applied (imagine manually, like by hand, removing the electrons at the P region, the diffusion will still happen) but as you said the applied electric field opposes the barrier field until it goes to zero then drift current flows.

You can also consider it that the barrier creates a large resistance (almost open circuit) at that drift current can't flow. Only diffusion can.
 
  • #3

FAQ: What is the purpose of the depletion region in P-N junction semiconductors?

1. What is a P-N junction semiconductor?

A P-N junction semiconductor is a type of semiconductor material that has been doped with impurities to create two regions with different electrical properties. The P-region is doped with a material that has an excess of positively charged particles, while the N-region is doped with a material that has an excess of negatively charged particles. The junction between these two regions creates a barrier that allows for the control of electrical current in the semiconductor.

2. How does a P-N junction semiconductor work?

A P-N junction semiconductor works by utilizing the properties of the two doped regions. The excess of positively charged particles in the P-region creates a positively charged layer, while the excess of negatively charged particles in the N-region creates a negatively charged layer. When the two regions are brought together, the opposite charges attract each other and create a depletion region, which acts as a barrier for electrical current. By applying a voltage across the junction, the depletion region can be reduced or enlarged, allowing for the control of electrical current.

3. What are the applications of P-N junction semiconductors?

P-N junction semiconductors have a wide range of applications, including in electronic devices such as diodes, transistors, and solar cells. They are also used in various sensors, such as light sensors and temperature sensors. P-N junctions are also an essential component in integrated circuits, which are used in computers, smartphones, and other electronic devices.

4. How are P-N junction semiconductors made?

P-N junction semiconductors are made by doping a pure semiconductor material, such as silicon or germanium, with impurities. The doping process involves adding small amounts of other elements, such as boron or phosphorus, to the semiconductor material. This changes the electrical properties of the material and creates the P and N regions necessary for a P-N junction.

5. What are the advantages of using P-N junction semiconductors?

P-N junction semiconductors have several advantages, including their small size, low cost, and high efficiency. They also have the ability to control the flow of electrical current, making them essential components in electronic devices. Additionally, P-N junctions can be easily integrated into complex circuits, allowing for the creation of advanced electronic systems.

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