Space charge width pn junction

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Homework Help Overview

The discussion revolves around calculating the width of the space charge region in a pn junction under reverse bias conditions. The specific context involves a silicon pn junction at room temperature with given doping concentrations.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • The original poster attempts to apply a formula for calculating the space charge width but expresses uncertainty about the calculation of the Fermi energy. Other participants question the relevance of the Fermi energy in the formula and seek clarification on the permittivity value used in the calculations.

Discussion Status

The discussion is ongoing, with participants providing feedback on the formula used and clarifying terms related to the problem. There is no explicit consensus yet, but guidance has been offered regarding the formula's components.

Contextual Notes

Participants are working with specific values for doping concentrations and a reverse bias voltage, and there is an assumption about the material properties of silicon at a given temperature.

MorrowUoN
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Homework Statement



Calculate the width of the space charge region in a pn junction when a reverse biased voltage is applied. Consider a silicon pn junction at T=300K with doping concentrations of Na=10^16 cm^-3 and Nd=10^15 cm-3. Assume that Ni=1.5*10^10 cm-3 and VR=5V

Homework Equations


W=((2Ef(Vbi+Vr)/e)((Na+Nd)/((Na*Nd))))^1/2

The Attempt at a Solution



I correctly calculated the in built potential to be 0.635V however, I do not know how to calculate the fermi energy
 
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Check that formula again. It does not involve the Fermi energy.
 
phyzguy said:
Check that formula again. It does not involve the Fermi energy.

What is the value of epsilon in the formula attached?
 

Attachments

  • f05651bb2afeca1e83a68bd340cc6fbb.png
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It's the permittivity of the material.
 

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