JEE Main · 2021 · 24 Feb 2021 · Shift 2 · Semiconductors

Zener breakdown is field emission: under reverse bias the electric field inside the depletion layer itself tears valence electrons out of their covalent bonds and lifts them straight into the conduction band. Heavy doping on both sides of the junction supplies a large density of ionised impurities, and the depletion layer can hold the contact potential across so dense a charge only by remaining very narrow, well under a micrometre. A modest reverse voltage across such a thin layer gives a field of about $10^8\mathrm{V}{\mathrm{m}}^{-1}$, which is strong enough for this tunnelling. Zener breakdown therefore occurs in a junction that is heavily doped on both sides and has a narrow depletion layer.