Electron Devices

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Arulmigu Meenakshi Amman college of Engineering
Vadamavandal-604410.
Prepared by,
V.Umapathy,
Prof./Mech.
Important Questions and Answers
EC25C01- Electron Devices
Syllabus
1. Semiconductor: Types, Conductivity, Electron energy levels and energy band diagram,
Carrier concentration, Mass action law, Characteristics and behavior of intrinsic
semiconductors, Variation in properties with temperature, Carrier drift and diffusion, Current
density equation, Excess carrier generation and recombination rates, Carrier life time.
Continuity equation.
Activity: Virtual demonstration of energy levels, Drift and diffusion current.
2. PN Junction Diodes: Energy band diagram of open-circuited PN junction, Forward and
reverse bias characteristics, Diode resistance, Transition and diffusion capacitance, Effect of
temperature on diode behavior, Applications of PN junction diodes.
Special Diodes: Zener diode – breakdown mechanisms and voltage regulation, Varactor
diode, Tunnel diode, Photo diode – construction, operation, and applications.
Activities: Virtual demonstration of characteristics of junction diodes, Design of a constant
voltage regulator using Zener Diode.
3. Bipolar Junction Transistors: Construction, working, characteristics in CB, CE, and CC
configurations, regions of operation, current gain, input/output characteristics, Early effect.
Other Devices: Multi-emitter transistor – construction and applications.
Practical: Input and Output characteristics of Characteristics of BJT.
4. Field Effect Transistors: JFET – construction, working, characteristics, parameters.
MOSFET, MOS capacitor, depletion and enhancement modes, nMOS and pMOS, threshold
voltage, transfer and output characteristics. CMOS – introduction and basic operation.
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Practical: Input and Output characteristics of Characteristics of JFET, MOSFET.
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5. Thyristors: Shockley diode, Silicon Controlled Rectifier (SCR), TRIAC and DIAC –
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operation and applications, Thyristor protection techniques.
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Unijunction Transistor (UJT): Construction, characteristics and application as relaxation
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oscillator.
Optoelectronic Devices: LED, LCD, Photo transistor, Opto-coupler – principle,
characteristics and applications. Power MOSFETs: Construction, switching characteristics
and applications in power circuits.
Practical: VI characteristics of SCR, UJT.
S.No Description
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Unit-I
Semiconductor
Introduction
Semiconductor Basics
- Materials with conductivity between conductors & insulators
- Types: Intrinsic, Extrinsic (N-type, P-type)
- Conductivity depends on carrier concentration

Energy Bands
- Valence band: bound electrons
- Conduction band: free electrons
- Bandgap: energy gap between bands
- Insulators: large gap
- Conductors: overlapping bands
- Semiconductors: small gap

Carrier Concentration
- n: electron concentration
- p: hole concentration
- Intrinsic: n = p = ni

Mass Action Law
- n * p = ni²

Intrinsic Semiconductors
- Pure semiconductors
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- Conductivity increases with temperature
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Carrier Transport
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- Drift: electric field
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- Diffusion: concentration gradient
- Current density: J = σE + qD(dn/dx)

Excess Carriers
- Generated by light, heat
- Recombine: electron + hole
- Lifetime: τ

Continuity Equation
- dn/dt = G - R + (1/q)∇J
- Describes carrier dynamics
Basic Concepts
Semiconductor Basics
- Materials with conductivity between conductors & insulators
- Types: Intrinsic (pure), Extrinsic (doped - N-type, P-type)
- Used in electronics: diodes, transistors

Energy Bands
- Valence band: electrons bound to atoms
- Conduction band: free electrons (conduct electricity)
- Bandgap (Eg): energy gap between bands
- Insulators: large Eg
- Conductors: no gap (overlapping)
- Semiconductors: small Eg (~1 eV)

Carrier Concentration
- n: electron concentration (conduction band)
- p: hole concentration (valence band)
- Intrinsic: n = p = ni (intrinsic concentration)

Mass Action Law
- n * p = ni²
- Applies to intrinsic & extrinsic semiconductors

Intrinsic Semiconductors
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- Pure semiconductors (e.g., Si, Ge)
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- Conductivity increases with temperature
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- Electrons jump to conduction band
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Temperature Effect
- More electrons in conduction band at high T
- Conductivity increases
Carrier Transport
- Drift: movement due to electric field
- Diffusion: movement due to concentration gradient
- Current density: J = qnμE + qD(dn/dx)

Excess Carriers
- Generated by light, heat, etc.
- Recombine: electron + hole
- Lifetime (τ): time before recombination

Continuity Equation
- dn/dt = G - R + (1/q)∇J
- Describes carrier dynamics.
Two Marks QA
1. What is a semiconductor?
- Material with conductivity between conductor & insulator.
2. Define intrinsic semiconductor.
- Pure semiconductor (e.g., Si, Ge).
3. What is the mass action law?
- n * p = ni².
4. How does temperature affect conductivity?
- Increases with temperature.
5. Define drift & diffusion.
- Drift: electric field movement. Diffusion: concentration gradient.
6. What is carrier lifetime?
- Time before recombination.
7. Write the continuity equation.
- dn/dt = G - R + (1/q)∇J.
8. What is a p-type semiconductor?
- Doped with acceptor atoms (e.g., B in Si).
9. Define bandgap.
- Energy gap between valence & conduction bands.
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10. What is current density equation?
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- J = qnμE + qD(dn/dx).
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13 and 15 Marks QA
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1. Explain energy band diagram of semiconductors.
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