PN Junction Diodes

A Brief Description Definitions The Depletion Region Varying VA Diode Currents
The Equation Derivations from the Ideal Let's Draw! Related Topics


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 x. 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 pn junction and its characteristics are the basis of almost every semiconductor device made.

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