- Moving dots: red = hole, blue
- Colored regions: red = p-type, blue
- dp = excess hole concentration at the depletion boundary
- dn=excess electron concentration at the depletion boundary.
- Lp = hole diffusion length
- Ln = electron diffusion length.
- I = total current
- In(x) = electron current (blue curve)
- Ip(x) = hole current (red curve).
- The diagram in the middle may be viewed as a band diagram, but the
band banding across the depletion region is not shown here. The numerical
values are for a Si pn junction diode.
- The diffusion process and the recombination process together produce
an exponential concentration profile for the minority holes, as can be
seen in the second diagram (lower-right, red). At a constant forward-bias,
the number of holes injected across the junction per unit time equals the
number of holes lost by recombination, thus establishing a steady state
(i.e., constant in time).
- The hole component of the total current is shown by the red curve in
the third figure. Going from left to right, the hole current in p-type
region is drift current (due to small electric field in the neutral p-region,
red), drift current in the depletion region (due to the built-in field),
and diffusion current in the n-side (blue) due to the concentration gradient.
The excess minority hole concentration reaches zero eventually.
- Electrons (blue) are injected from n-side (blue) to the p-side (red)
across the junction (or depletion region, gray). They go through the same
process as holes.
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