Saturday, July 16, 2016

Section C - Semiconductors

Scope of Syllabus
Semiconductors
Energy bands in solids; energy band diagrams for distinction between conductors, insulators and semi-conductors -intrinsic and extrinsic; electrons and holes in semiconductors.

Elementary ideas about electrical conduction in metals [crystal structure not included]. Energy levels (as for hydrogen atom), 1s, 2s, 2p, 3s, etc. of an isolated atom such as that of copper; these split, eventually forming ‘bands’ of energy levels, as we consider solid copper made up of a large number of isolated atoms, brought together to form a lattice; definition of energy bands - groups of closely spaced energy levels separated by band gaps called forbidden bands.


An idealised representation of the energy bands for a conductor, insulator and semiconductor; characteristics, differences; distinction between conductors, insulators and semiconductors on the basis of energy bands, with examples; qualitative discussion only; energy gaps (eV) in typical substances (carbon, Ge, Si); some electrical properties of semiconductors. Majority and minority charge carriers electrons and holes; intrinsic semiconductors and extrinsic semiconductors, doping, p-type, n-type; donor and acceptor impurities.




Junction diode; depletion region; forward and reverse biasing, V-I characteristics; half wave and a full wave rectifier; solar cell, LED and photodiode. Zener diode.

Junction diode; symbol, simple qualitative description only [details of different types of formation not included]. [Bridge rectifier of 4 diodes not included]. Simple circuit diagrams of rectifier and input/output graphs, function of each component in the electric circuits, qualitative only.
Elementary ideas on solar cell, photodiode and light emitting diode (LED) as semi conducting diodes. Importance of LED’s as they save energy without causing atmospheric pollution and global warming.

Zener diode, V-I characteristics and circuit only of voltage regulator.



Junction transistor; n-p-n and p-n-p transistors; current gain in a transistor and transistor as an amplifier in common emitter mode (only circuit diagram and qualitative treatment); transistor as a switch; oscillator.

Simple qualitative description of construction-emitter, base and collector; n-p-n and p-n-p type; symbol showing direction of current in emitter-base region (one arrow only)- base is narrow; current gain in a transistor.

Common emitter configuration only, characteristics; IB vs VBE and IC vs VCE with circuit diagram [no numerical problem]

Common emitter transistor amplifier-correct diagram; qualitative explanation including amplification, wave form and phase reversal. [relation between α and β, not included, no numerical problems].

Transistor as a switch (qualitative only).

Circuit diagram and qualitative explanation of a simple oscillator.

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