EGRE 303 Lab 3: PN Junction Lab – Exploring PN Junction Diode

Project Goal:
Your task in this laboratory project to explore and understand operation of PN junction diodes and gain insight
into some limitation associated with a simplified the textbook model. The simulation tool is available at
Nanohub. (nanohub.org).
We have discussed in class the depletion approximation. The depletion approximation is extremely useful, when
it is valid, so it is important to understand its limitations. In this work, you will compare the results of depletion
approximation analyses of PN junctions with the “exact” solution obtained by solving the semiconductor
equations directly by numerical simulation using the computer program.

Part 1: Analytical calculations with the depletion approximation:
1) A Si step junction maintained at room temperature under equilibrium conditions has a
p-side doping density of NA = 2 x 1015 /cm3
and an n-side doping of ND = 1015/cm3.

EGRE 303 Lab 3: PN Junction Lab – Exploring PN Junction Diode

Use the depletion approximation to compute:
(a) Vbi
(b) The depletion layer boundaries, xp, xn, and the depletion width, W
(c) The electric field at the junction.
(d) The electrostatic potential at the junction.
(e) Plot of the charge density, electric field, and electrostatic potential as a function of position, as well as I-V
characteristics.
2) Repeat problem 1), still using the depletion approximation, but set the p-side doping to NA
= 3 x 1017
/cm3
and keep the n-side doping at ND = 1016
/cm3
. Compute the same quantities
as in problem 1) and compare the results to those of problem 1).
Part 2: “Exact” numerical simulations and their comparison with “textbook” result:
Set the doping densities on the P and N sides of the junction to correspond to those in problem 1) above.
Set the length of the P-region to be 1.0 micrometer and for the N-region, 2.0 micrometers. Be sure that you have
selected “Si” as the material and that the temperature is “300K.”
Simulate the parameters of the defined structure .
3a) Use the potential vs. position plot to determine the built-in potential of the PN junction. Compare your
answer to the depletion approximation result. (Remember that potentials always have an arbitrary reference, so
don’t be confused by the fact that the potential is not zero on one side of the junction.)
3b) Use the carrier density vs. position plot to estimate the width of the depletion layers on the P and N sides, xp
and xn. First, plot side-by-side the carrier density vs. position assumed in the depletion approximation and the
numerically generated plot, then determine whether the depletion approximation results are reasonable. Explain