PN Junction Diodes
A pn junction is formed by diffusing a p-type material to
an n-type wafer (and there are several other ways as well, see your
text). At the point of the junction, which we call the metallurgical junction,
is where ND - NA
= 0. The doping profile is our starting point to analyze pn
junction electrostatics, since it combines the information given
for ND and NA
. It gives us enough information to sketch the band diagram, the
electrostatic potential V, the electric field E,
and charge density
r, as a function of
This is an exercise you should be able to do without consulting the book.
Try it now!
There are many different applications with pn junctions.
Photodetectors, solar cells and LEDs, are optoelectronic devices that have
a pn junction. BJTs, J-FETs and MESFETs, are devices that
have more than one pn junction. Last, but not least, the
junction and its characteristics are the basis of almost every semiconductor