SUMMARY

The chapter's own bullet-point summary restates every major definition and law in condensed one-line form: energy bands classify solids into metals/insulators/semiconductors; electrons are majority carriers in n-type and holes are minority (and vice versa in p-type); an unbiased p-n junction has a depletion region of immobile ions with no mobile carriers; forward bias shrinks the depletion region and lets the diode conduct like a closed switch once the barrier potential is crossed, while reverse bias widens it and the diode acts as an open switch; rectification converts AC to DC, with the half wave rectifier passing one half of the input (pulsating output) and the full wave rectifier passing both halves at twice the efficiency; Zener and avalanche breakdown are the two reverse-breakdown mechanisms, Zener in heavily doped junctions under strong field, avalanche in lightly doped junctions via carrier collisions; the Zener diode is a heavily doped diode purpose-built to work in reverse breakdown; the LED emits light on forward bias via recombination, the photodiode converts absorbed photons into a photocurrent under reverse bias, and the solar cell converts light directly into electricity by the photovoltaic effect; a BJT (NPN or PNP) has emitter, base and collector regions and operates in common base/common emitter/common collector configurations, with $\alpha=I_C/I_E$ and $\beta=\Delta I_C/\Delta I_B$ as the two current-gain figures; in common emitter mode a BJT functions as a switch (saturation/cut-off) or, with 180-degree phase reversal, as an amplifier (active region); an amplifier plus a tank circuit plus positive feedback …