# Homework Help: Semiconductor Electrical Field?

1. Oct 18, 2012

1. The problem statement, all variables and given/known data

The electron concentration in silicon at T = 300K is: n(x) = 1016e(-x/18) cm-3 where x is measured in μm and is limited to 0 ≤ x ≤ 25. The electron diffusion coefficient, Dn = 25 cm2/s and the electron mobility is μn = 960cm2/Vs. The total electron current density is constant and = Jn = -40A/cm2. The electron current has both diffusion and drift current components.

Determine the electric field as a function of x which must exist in the semiconductor.

2. Relevant equations

εx = (-kT/e)* d/dx (ln*Nd(x))

3. The attempt at a solution

Pretty lost here. My first instinct was to attempt a solution with the above equation by taking the derivative of n(x). Firstly, I was thrown off by the given range of x. Should I incorperate it somehow? Secondly, I'm not even sure if Nd(x) is the same quantity as the given n(x). How could I infer this from the question?

If anyone could put me on the right track at least with what equation to use, I would greatly appreciate it!