Built-in potential (φbi)

Beginner

The natural “hill” at a p-n junction that stops electrons and holes from mixing any further.

Novice

The voltage across a p-n junction at equilibrium, set up by the fixed charges in the depletion region. In silicon it is typically 0.6–1 V depending on doping.

Expert

$\phi_{\mathrm{bi}} = (kT/q)\ln(N_{\mathrm{a}} N_{\mathrm{d}}/n_{\mathrm{i}}^2)$ . It cannot be read with a voltmeter, because the metal-semiconductor contact potentials around the loop cancel it exactly.

Explained in Bands, doping and the p-n junction (Transistors).

See also: p-n junction, Depletion region.

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