Chapter 14 - Semiconductor Electronics

Beginner

Topper

1. Conductors Insulators Semiconductors - Band Theory

Solids have energy bands: valence filled, conduction empty, gap Eg between. Conductor Eg=0 overlapping free. Insulator Eg~6 eV large cannot jump. Semiconductor Eg~1 eV Si 1.1 Ge 0.7 small can jump with heat light. Conductivity sigma=n e mu.

Conductor Eg=0 overlapping | Insulator Eg~6 eV no conduction | Semiconductor Eg~1 eV Si 1.1 Ge 0.7 | sigma=n e mu

Visual Learning Method: Bands overlap no gap conductor, large gap insulator, small gap semiconductor, electrons jumping with heat.

Daily Analogy: Wall height: conductor no wall, insulator 6m wall cannot climb, semiconductor 1m small jump with push heat.

Band Theory

Revision Points - Easy:

Conductor no gap free.
Insulator large gap ~6 eV no free.
Semiconductor small gap ~1 eV can jump.
Si 1.1 eV Ge 0.7 eV.

2. Intrinsic & Extrinsic - Doping

Intrinsic pure Si Ge n=p=ni low. Extrinsic doping adds impurity. n-type 5th group phosphorus extra electron donor majority e-. p-type 3rd group boron hole acceptor majority h+. n p=ni^2.

Intrinsic pure n=p=ni | n-type 5th donor extra e- majority e- | p-type 3rd acceptor hole majority h+ | n p=ni^2

Visual Learning Method: Pure Si lattice, n-type extra electron, p-type hole, donor acceptor levels.

Daily Analogy: Extra students standing extra electrons, empty chairs holes easier movement.

Intrinsic & Extrinsic - Doping

Revision Points - Easy:

Pure n=p.
n-type add P 5 electrons extra.
p-type add B 3 creates holes.

3. p-n Junction - Depletion Region

p and n join electrons diffuse n to p holes p to n recombination leaves ions - p -ve + n +ve creates field barrier Vb 0.7V Si 0.3V Ge depletion no carriers. Forward p+ n- barrier down current flows. Reverse p- n+ barrier up almost no current.

p-n diffusion ions depletion no carriers | Barrier 0.7V Si 0.3V Ge | Forward p+ n- down current | Reverse p- n+ up blocks

Visual Learning Method: Depletion ions barrier 0.7V forward shrinks reverse widens.

Daily Analogy: No man's land between countries guards ions, forward lowers wall, reverse raises wall.

p-n Junction

Revision Points - Easy:

p n join depletion ions no carriers.
Barrier 0.7V Si.
Forward p+ n- allows current.
Reverse blocks.

4. Diode Characteristics & Rectifier

Diode I-V forward after knee 0.7V exponential rise reverse tiny saturation until breakdown. Rectifier AC to DC half wave one diode half cycle 50% full wave two diodes centre tap or bridge 4 diodes both halves 81% filter capacitor smooths.

Diode forward exponential after 0.7V knee reverse tiny breakdown | Half wave one diode half | Full wave two or bridge both | Capacitor filter smooths

Visual Learning Method: I-V curve knee reverse breakdown half wave half pulses full wave both halves bridge 4 capacitor smooth.

Daily Analogy: One-way valve water only one direction rectifier makes alternating flow one direction tank stores steady flow.

Diode & Rectifier

Revision Points - Easy:

Diode one way after 0.7V.
Reverse almost no current till breakdown.
Half wave one diode half AC.
Full wave both halves.
Capacitor smooths DC.

5. Zener & Optoelectronic Devices

Zener heavily doped thin depletion reverse breakdown sharp Vz non-destructive as voltage regulator maintains Vz. Photodiode reverse bias light creates e-h current increases with intensity. LED forward e-h recombine emit photon colour depends on Eg GaAs IR GaP red green. Solar cell no bias light creates e-h separated by junction field gives voltage converts light to electricity.

Zener heavily doped reverse Vz regulator constant | Photodiode reverse light to current | LED forward light GaAs GaP | Solar cell light to electricity no bias

Visual Learning Method: Zener Vz regulator photodiode light current LED forward glows solar cell sun electricity.

Daily Analogy: Zener pressure valve constant, photodiode eyes light to current, LED electricity to light, solar opposite light to electricity.

Zener & Optoelectronic

Revision Points - Easy:

Zener reverse breakdown Vz regulator.
Photodiode reverse light detector.
LED forward light colour material dependent.
Solar cell light to electricity.

6. Transistor - BJT Working

BJT npn pnp emitter heavy doped supplies carriers base thin lightly doped controls collector moderate collects. Active EB forward CB reverse. npn emitter injects electrons into base few recombine small Ib most go collector Ic = beta Ib beta 50-200 IE=IB+IC.

Emitter heavy base thin light collector moderate | Active EB forward CB reverse | npn e- injection pnp hole | IE=IB+IC IC=beta IB beta 50-200

Visual Learning Method: npn pnp layers emitter base collector thin base electron flow small base controls large collector.

Daily Analogy: Tap small handle controls big water flow collector emitter source base gate.

Transistor BJT

Revision Points - Easy:

Emitter heavy supplies carriers.
Base thin light few recombine small Ib.
Collector collects Ic.
IE=IB+IC small base controls large collector.

7. Transistor as Amplifier & Switch

CE amplifier input base small ac voltage gives large collector current through Rc large output gain Av=-Rc/re phase 180 inverted. As switch saturation both forward Vce~0.2 ON cut-off both reverse Vce~Vcc OFF used digital.

CE amplifier small base large collector gain Av=-Rc/re phase 180 | Switch saturation ON Vce~0.2 cut-off OFF Vce~Vcc

Visual Learning Method: CE amplifier small sine large inverted switch saturation ON cut-off OFF.

Daily Analogy: Amplifier loudspeaker small voice big sound switch tap open ON closed OFF for computer 1 0.

Amplifier & Switch

Revision Points - Easy:

Small base gives large collector output amplifier.
Output inverted 180 in CE.
Saturation ON cut-off OFF switch for computer.

8. Logic Gates & Applications

Logic gates building blocks computers AND A.B both 1 gives 1 OR A+B any 1 gives 1 NOT inverts 0->1 1->0 NAND AND+NOT universal NOR OR+NOT universal can make all gates. Truth tables important. IC chips contain many gates in one package.

Visual Learning Method: AND OR NOT symbols truth tables NAND NOR universal IC chip mobile computer.

Daily Analogy: AND both keys safe both needed OR either key any opens NOT opposite switch.

Logic Gates & Applications

Revision Points - Easy:

AND both 1 then 1.
OR any 1 then 1.
NOT opposite.
NAND NOR universal can make all.
IC many gates in chip phones computers.

Gold Reference Table

Concept	Formula / Easy Fact	Daily Life Visual
Band gap	Conductor 0 Insulator ~6 Semi ~1 Si 1.1 Ge 0.7	Wall height
Intrinsic	n=p=ni	Pure low
n-type	5th donor P As extra e- majority e-	Extra student
p-type	3rd acceptor B Al hole majority h+	Empty chair
p-n barrier	Vb 0.7 Si 0.3 Ge	No man's land
Diode I-V	Forward exponential after knee Reverse tiny breakdown	One way valve
Rectifier half	One diode half AC	Half pulses
Rectifier full	2 diodes centre tap or bridge 4 both halves	Both halves DC
Zener	Heavily doped reverse Vz regulator	Pressure valve constant
Photodiode LED Solar	Photo reverse light to current LED forward light Solar light to electricity	Detector bulb panel
Transistor	Emitter heavy base thin light collector moderate IE=IB+IC IC=beta IB	Tap small controls big
CE Amplifier	Av=-Rc/re phase 180	Small voice big sound inverted
Switch	Saturation ON Vce~0.2 Cut-off OFF Vce~Vcc	ON OFF digital
AND OR NOT NAND NOR	AND both 1 OR any 1 NOT opposite NAND NOR universal	Keys safe