Semiconductor Devices and Communication Systems
Semiconductor Devices and Communication Systems covers band theory, doping, the p-n junction, rectifiers, Zener regulation, transistors, logic gates, and the elements of modulation and communication.
Core rules
- Band gaps separate conductors (~0 eV), semiconductors (~1 eV) and insulators (above about 3 eV).
- Intrinsic material has n(e) = n(h); pentavalent donors give n-type, trivalent acceptors give p-type.
- In a p-n junction diffusion builds a depletion layer with a barrier potential, about 0.7 V for silicon and 0.3 V for germanium. Forward bias narrows the layer; reverse bias widens it and leaves only a small leakage current.
- A half-wave rectifier uses one diode; full-wave uses two with a centre tap or four in a bridge; a capacitor filter smooths the output.
- A Zener diode operates in reverse breakdown as a voltage regulator.
- Transistor relations: I(E) = I(B) + I(C), α = I(C)/I(E), β = I(C)/I(B); the CE amplifier inverts phase by 180°.
- Communication needs modulation; know AM and FM, bandwidth, sky-wave and space-wave propagation, and optical fibre.
Worked example
A CE transistor has β = 100 and base current 20 μA. Then I(C) = βI(B) = 2.0 mA and I(E) = 2.02 mA. Its α = I(C)/I(E) = 0.99, just below unity as expected for a good transistor.
Traps
Calling the depletion region neutral (it holds immobile ions); assuming a diode conducts in reverse bias; swapping α and β; forgetting a bridge rectifier needs four diodes.