Semiconductor P-N Junction

P-N Junction

Applied voltage 0.30 V

Doping concentration 1.0×

Temperature 300 K

Depletion width

–

Diode current

–

Barrier V

–

Carriers/frame

–

How it works

A p-n junction is formed where p-type silicon (doped with boron, carrying mobile positive "holes") meets n-type silicon (doped with phosphorus, carrying mobile free electrons). Near the boundary, electrons diffuse into the p-side and holes diffuse into the n-side; they recombine and leave behind fixed, charged dopant ions — a carrier-free depletion zone whose internal electric field opposes further diffusion. Applying a forward voltage (p-side positive) narrows this barrier and lets current flow easily; a reverse voltage (n-side positive) widens it and current is almost completely blocked.

I = I₀·(e^(qV / kT) − 1)
W ∝ √(Vbi − V) / N_doping

Applied voltage — positive values forward-bias the junction (barrier shrinks, current rises exponentially); negative values reverse-bias it (barrier grows, current is suppressed).
Doping concentration — higher doping packs more fixed ions into a thinner depletion zone, raising the built-in field for the same voltage.
Temperature — higher T gives carriers more thermal energy (kT), increasing both diffusion and the reverse leakage current I₀.
Field lines — toggle the internal electric field arrows across the depletion zone that resist carrier diffusion at equilibrium.

Real-world relevance: this exact mechanism — a controllable depletion zone — is the switch at the heart of every diode, LED, solar cell and MOSFET gate, and by extension every one of the transistors that make up a modern semiconductor chip.

Electron (n-side) Hole (p-side) Depletion zone

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