Applet Tutorial

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 your answer.
What does this relation mean physically about the total space charge ? Check your answer.

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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 diagram).
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.

Answer:

N_d x_n = N_a x_p.
Space charge neutrality: that is, the total positive charge ( N_d x_n) due to the uncompensated ionized donors is equal to the total negative charge ( N_a x_p) due to the uncompensated ionized acceptors.