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- Depletion thickness
- The depletion thicknesses, xp and xn,
represent the distance of the depeletion edge from the junction.
- Change the doping level of one side at steps of a factor ten. Record
on paper both depletion thicknesses at each doping level.
- Based on your data, what is the mathematical relationship of xp
and xn to Na and Nd ? Write down
a single equation that involves all these four parameters. Check
- What does this relation mean physically about the total space charge
? Check your answer.
- Hide the applet page by scrolling down the text or minimizing your
- Draw on paper the band diagram of PN junction for Na = 1E16 and Nd
= 1E15. Make the band diagram correct both quantitatively (in the relative
depletion thickness of the two sides) and qualitatively (shape of band
- Use the applet to check if your diagram is correct.
- Can you draw the band diagram for a PNP structure where Na = 1E18,
Nd = 1E17, and Na = 1E15 ? Assume that the N-layer thickness is greater
than the sum of the depletion thicknesses from the two junctions.
- Nd xn
= Na xp.
- Space charge neutrality: that is, the total
positive charge ( Nd xn )
due to the uncompensated ionized donors is equal to the total negative
charge ( Na xp ) due
to the uncompensated ionized acceptors.