CBSE Class 12 Board Examination

Chapter 6: Semiconductor Electronics: Materials, Devices and Simple Circuits

Summary

Solids are classified by their energy bands: conductors have overlapping or partly filled bands, insulators a large forbidden gap, and semiconductors a small gap that allows modest conduction. In a pure (intrinsic) semiconductor, equal numbers of electrons and holes carry current. Doping with pentavalent atoms gives an n-type semiconductor (electrons as majority carriers) and with trivalent atoms a p-type (holes majority). Joining the two forms a p-n junction, where diffusion creates a depletion region and a built-in barrier potential. The junction conducts readily under forward bias but barely under reverse bias, acting as a diode whose characteristic curve shows this rectifying behaviour. Diodes are used in half-wave and full-wave rectifiers to convert AC to DC, while special diodes such as the Zener (voltage regulation), photodiode, LED and solar cell exploit junction properties for sensing and light. These devices, compact and reliable, replaced bulky vacuum tubes and form the foundation of all modern electronics, from power supplies and displays to the integrated circuits at the heart of computing and communication.

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