Ch 14 covers semiconductor physics — energy bands, intrinsic/extrinsic semiconductors, p-n junction diode, special diodes (LED, photodiode, solar cell), transistor, and logic gates.
Energy bands: valence band, conduction band, band gap (Eg). Conductors: overlapping bands. Insulators: large Eg (>3 eV). Semiconductors: small Eg (~1 eV, Si = 1.1). n-type: pentavalent doping (extra electron), p-type: trivalent doping (hole). p-n junction: depletion region forms at junction. Forward bias: barrier reduces, current flows. Reverse bias: barrier increases, very small current (breakdown at high voltage).
Rectifier: AC → DC using diode. Half-wave: single diode (one half-cycle). Full-wave: two diodes or bridge (both half-cycles). Special diodes: Zener (voltage regulation), LED (light emission), photodiode (light detection), solar cell (light → electricity). Transistor (BJP): emitter-base-collector, amplification β = I_C/I_B. Logic gates: AND (A·B), OR (A+B), NOT (Ā), NAND, NOR (universal gates), XOR.
Download: https://ncert.nic.in/textbook/pdf/leph206.pdf | Part II: https://ncert.nic.in/textbook/pdf/leph2ps.zip
Silicon has a wider band gap (1.1 eV vs 0.7 eV for Ge), giving better performance at higher temperatures (less leakage current). Silicon is also abundantly available (second most common element in Earth's crust, from sand). Silicon oxide (SiO₂) forms a natural insulating layer, making fabrication of integrated circuits easier.
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