Chapter 19 — Chapter 19 — Electronics

Semiconductors (silicon, germanium) have conductivity between conductors and insulators; doping makes n-type (extra electrons, e.g., with phosphorus) and p-type (holes, e.g., with boron). A p–n junction diode allows current in one direction only. At the junction a depletion region (no free carriers) forms with a barrier potential (~0.7 V Si). Forward bias (p to +): depletion region narrows, barrier lowered, large current flows. Reverse bias: depletion region widens, only tiny leakage current; very high reverse voltage causes breakdown — large current and heating destroy the diode, showing it has a maximum reverse voltage rating (physical limit). Used as rectifiers.