Question about neutral region in Derivating Shockley equation

[alexyangfox]

question about "neutral region" in Derivating Shockley equation

Hey guys.
I met a problem when derivating the Shockley equation.
a few steps before I finally get the Shockley equation , I met the Equation
in the attachment.

the book said , because there's no electric field in the neutral region.
So the E is 0,that means the second term disappears.

But why?
When there's a voltage say 5v Across the Pn junction(say,forward bias) ,how could it be possible that there's no electric field in the neutral region?

Or the Ideal diode model computes the "voltage" in the depletion layer,say twist the bands?



thanks,
Best regards.

 

[eljose79]

Hello there,

Thank you for your question about the "neutral region" in the Shockley equation. The neutral region refers to the area in a PN junction where there is no net electric field present. This means that the electric field is equal in magnitude and opposite in direction on both sides of the junction, resulting in a net electric field of zero.

In order to understand why the second term in the equation disappears in the neutral region, it is important to understand the behavior of the electric field in a PN junction. When a voltage is applied across the junction, it creates a depletion region where there is a difference in charge density between the P and N regions. This difference in charge density creates an electric field that opposes the applied voltage.

In the neutral region, the electric field is zero because the depletion region is balanced by the diffusion of charge carriers from the P and N regions. This means that the second term in the equation, which represents the electric field, becomes zero as well.

As for your question about the Ideal diode model, it does not consider the voltage in the depletion layer or the twisting of bands. Instead, it simplifies the behavior of a diode by assuming that it is either fully conductive or fully non-conductive, with no voltage drop across it.

I hope this helps clarify the concept of the neutral region in the Shockley equation. Let me know if you have any further questions.