Space charge width pn junction

[MorrowUoN]

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 N_a=10^16 cm^-3 and N_d=10^15 cm-3. Assume that N_i=1.5*10^10 cm-3 and V_R=5V

Homework Equations

W=((2E_f(V_bi+V_r)/e)((N_a+N_d)/((N_a*N_d))))^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

 

[phyzguy]

Check that formula again. It does not involve the Fermi energy.

 

[MorrowUoN]

Check that formula again. It does not involve the Fermi energy.

What is the value of epsilon in the formula attached?

 

[marcusl]

It's the permittivity of the material.