The drift and diffusion currents under equilibrium

In summary, the person is asking for help in understanding a part of their book which discusses the pn junction in equilibrium. They question why there is drift current in the equation, even though the total current is supposed to be zero in equilibrium. They also mention that they are confused about the concept of diffusion and drift currents and their existence in a short period of time. They ask for an explanation of the next part and also mention an unrealistic phenomenon, charge accumulation. The person also expresses confusion about how each side of the equation can be zero. The other person responds by explaining that after diffusion, all electrons and holes are spread equally and questions how current can continue in this situation. They also mention their age and offer to help explain the concept based on
  • #1
anhnha
181
1
Can you help me explain this part from my book?
attachment.php?attachmentid=59370&stc=1&d=1370675472.jpg

attachment.php?attachmentid=59367&stc=1&d=1370673591.jpg


In equilibrium, the pn junction has no external connections, i.e., the terminals are open and no voltage is applied across the device.
If so, I wonder why there is drift current in the equation above. In equilibrium, the total current is zero but I don't understand how can they get the equation.
Is it right that in equilibrium, the total current is zero but each current (drift and diff currents) are not necessary to be zero?

PS: I have just seen the image. It is relatively clear now. In equilibrium, the net current is zero.
From that I can get the equation above. However, I am confused about these currents. I think they are only exist in a short of time, right?
After that time:
The diffusion is zero when the concentration of electrons and holes are equal in P and N sandwiches.
The dift currents are zero when all minority charge carriers are depleted.
If possible, can you explain about the next part?
 

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  • #2
@anhnha... I see you are still active now. Can you explain to me what the next part in the following sentence is?

anhnha said:
If possible, can you explain about the next part?
 
  • #3
Thank you!
Could you explain about unrealistic phenomenon here?
Why is there a charge accumulation?
I don't see how is each side of equation 2.61 can be zero.
For the right hand side part, the total current always flows from p to n and in the left hand side the total current always flows from p to n.
I don't see how possible it is to assume that each side of the equation is zero.

With the next part, I meant to say that because there is a limited number of electrons on each side of the pn junction so after the diffusion all electrons and holes are spread equally so how is it possible for the current to continue here?
I think I can answer it now. Because of the drift current, the concentration will never be equal so there is always diffusion current.
 
  • #4
OK. The problem with my understanding of this phenomenon is that it does not contain all these terms. Can I know how old you are? Because I have just learned this topic myself (I am 17), and I could help you understand it the way I understood it, because my way makes a little more sense physically. But that is only if you want me to.

PS: I hope you are not female. Last time I checked, asking females their age was not chivalrous. :smile::oldbiggrin:
 

1. What is the difference between drift and diffusion currents under equilibrium?

Drift and diffusion currents are two types of electrical current that occur in a material under equilibrium conditions. Drift current is the movement of charge carriers, such as electrons or holes, in response to an applied electric field. Diffusion current, on the other hand, is caused by the random thermal motion of charge carriers and results in the net movement of charge from areas of high concentration to low concentration.

2. How are drift and diffusion currents related to each other?

Drift and diffusion currents are closely related and often occur simultaneously in a material. The total current in a material is the sum of the drift and diffusion currents. In some cases, diffusion may dominate over drift, while in others, drift may dominate over diffusion.

3. How does temperature affect drift and diffusion currents?

Temperature plays a significant role in determining the magnitudes of drift and diffusion currents. As temperature increases, the thermal energy of the charge carriers also increases, leading to higher diffusion currents. On the other hand, higher temperatures may also lead to increased collisions and scattering of charge carriers, resulting in lower drift currents.

4. Can drift and diffusion currents be controlled in a material?

Yes, drift and diffusion currents can be controlled by various factors such as the material's properties, temperature, and electric field strength. For example, the type of material, its purity, and the presence of impurities can affect the mobility of charge carriers and therefore impact the drift and diffusion currents.

5. What is the significance of understanding drift and diffusion currents in materials?

Understanding drift and diffusion currents is essential in the study and development of electronic devices. These currents play a crucial role in determining the behavior and performance of materials used in these devices. By understanding how drift and diffusion currents are affected by various factors, scientists and engineers can design and optimize materials for specific applications.

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