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Diodes Appendix A: The Depletion Region
As shown in Figure 2 below, the depletion region increases in the direction of the weakest field (the area of highest resistivity) as reverse voltage is applied. This expansion continues as the reverse voltage is increased until the stress on the field reaches the breakdown threshold.

Epitaxially-grown layers have very abrupt differences in resistivity layers while deep-diffused devices are less abrupt. This difference creates a variation in the depletion-region movement; that is, deep diffusion results in depletion- region movement in the N+ and P+ direction. The abrupt junctions in epitaxially-grown layers result in depletion-region expansion primarily toward the N+ layer.

Figure 2 - Depletion Regions of P-N junctions

Last revised: 21 May 2014