Questions about the Potential and E-Field directions of P-N junction

In summary, The depletion region in a PN junction is caused by the diffusion of electrons from the n-type material to the p-type material, which creates a local electric field that is strongest at the contact interface and decreases towards the end of both materials. The potential in the material remains negative towards the end of the p-type material and positive towards the n-type material. The E-field in the diagram points from right to left, but the intensity is represented as negative, indicating that "right" is considered positive. Additionally, since the electric field is the negative derivative of potential with respect to distance, the potential integrates to a constant once the electric field is zero.
  • #1
Sandbo
18
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Pn-junction-equilibrium-graphs.png


Hi, on re-visiting some basic ideas about PN junctions, I found I am confused with the depletion region diagram:

I understand that the depletion region originated from the diffusion current at the local contact of the p and n type material, the electrons diffuse from the n type to p type building a local E-Field, the field intensity is the strongest at the contact interface and decreases gradually towards the end of the material of both p and n type materials.

1. From the diagram above, why is the potential of the material remains a negative(towards the end of p-type) and positive(towards the n-type)?
Isn't it only the depletion region that will encounter a change in potential?
How come the whole right and whole left are positive and negative after all?:confused:

2. As the +ve ions are left at the right(n side) and -ve ions are created on the left(p side), I suppose the E-field points from the right to left(n to p), the arrow indicates this and makes sense.
However, from the E-Field graph, the intensity is a negative value, does it mean they are actually taking "right" as positive?

Thanks for reading:biggrin:
 
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  • #2
1. E points to the -x direction so E(x) is negative.

2. Since the electric field is the (negative) derivative of V wrt x, then V integrates to a constant once E = 0.
 

FAQ: Questions about the Potential and E-Field directions of P-N junction

1. What is a P-N junction?

A P-N junction is a boundary between two types of semiconductor materials, namely P-type and N-type. P-type materials have an excess of positively charged carriers (holes), while N-type materials have an excess of negatively charged carriers (electrons). When these two types of materials are brought together, they form a depletion region where electrons and holes recombine, creating a built-in electric field.

2. How does a P-N junction work?

In a P-N junction, the built-in electric field causes electrons and holes to diffuse across the junction, resulting in a flow of current. This flow of current can be controlled by applying a voltage across the junction, known as the bias voltage. The direction of the electric field and the flow of current are dependent on the direction of the bias voltage.

3. What is the potential barrier in a P-N junction?

The potential barrier is the energy difference between the conduction band of the N-type material and the valence band of the P-type material. It is created by the depletion region and prevents the flow of majority carriers (electrons in N-type and holes in P-type) across the junction in the absence of an external bias voltage.

4. How does the potential barrier affect the direction of the electric field in a P-N junction?

The potential barrier creates a built-in electric field that points from the N-type material to the P-type material. This electric field is responsible for the diffusion of electrons and holes across the junction, resulting in a flow of current. The direction of the electric field is opposite to the direction of the bias voltage.

5. What is the direction of the E-field in a reverse-biased P-N junction?

In a reverse-biased P-N junction, the bias voltage is applied in a direction that opposes the built-in electric field. This results in an increase in the width of the depletion region and a decrease in the flow of current. The direction of the electric field remains the same, from the N-type material to the P-type material.

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