Classification of Solids in Physics

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Questions and Answers

What is the conductivity range for semiconductors?

  • $10^{5} – 10^{6} ext{ } ext{Ω} ext{m}$
  • $10^{-5} – 10^{-6} ext{ } ext{Ω}^{-1} ext{m}^{-1}$ (correct)
  • $10^{-8} – 10^{-10} ext{ } ext{Ω}^{-1} ext{m}^{-1}$
  • $10^{2} – 10^{8} ext{ } ext{Ω}^{-1} ext{m}^{-1}$

Which characteristic is true for n-type semiconductors?

  • Ne > nh. (correct)
  • Major charge carrier is a hole.
  • Doping is from V-group elements.
  • It behaves as an insulator at room temperature.

What energy gap value range corresponds to semiconductors?

  • $E_g ≈ 0$
  • $E_g > 3 ext{ eV}$
  • $0 ext{ eV} < E_g < 5 ext{ eV}$
  • $0.2 ext{ eV} ≤ E_g ≤ 3 ext{ eV}$ (correct)

Which of the following is an example of an intrinsic semiconductor?

<p>Si (D)</p> Signup and view all the answers

What occurs during forward biasing of a p-n junction diode?

<p>The depletion layer decreases. (C)</p> Signup and view all the answers

Which material exhibits an energy gap of approximately 5.4 eV?

<p>Diamond (D)</p> Signup and view all the answers

What classifies a material as a conductor based on energy bands?

<p>Eg ≈ 0. (C)</p> Signup and view all the answers

What defines the conduction band in a solid?

<p>The band where electrons show conductivity. (D)</p> Signup and view all the answers

Flashcards

Conductor

A material that easily allows electric current to flow.

Semiconductor

A material with conductivity between a conductor and an insulator; conductivity increases with temperature.

Insulator

A material that does not allow electric current to flow easily.

Intrinsic Semiconductor

A pure semiconductor material.

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Extrinsic Semiconductor

A semiconductor material with impurities.

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n-type semiconductor

Extrinsic semiconductor with extra electrons as major charge carriers.

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p-type semiconductor

Extrinsic semiconductor with extra holes as major charge carriers.

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Valance Band

Energy band containing valence electrons in a solid.

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Conduction Band

Energy band where electrons move freely and conduct electricity.

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Band Gap Energy

Energy difference between valence and conduction bands.

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Conductor (Energy Gap)

Materials with overlapping valence and conduction bands; almost zero energy gap.

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Insulator (Energy Gap)

Materials with large band gap; electrons cannot easily jump to conduction band.

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Semiconductor (Energy Gap)

Materials with medium band gap; electrons can jump to conduction band with enough energy.

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p-n junction diode (Forward Bias)

Current flows easily when positive terminal is connected to p-side and negative terminal to n-side.

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p-n junction diode (Reverse Bias)

Current flow is restricted; depletion region widens.

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Study Notes

Classification of Solids

  • Conductor: Easily conducts electricity; σ = 102-108 Ω-1m-1; ρ = 10-8-10-2 Ωm

  • Semiconductor: Conducts at higher temperatures; σ = 10-5-106 Ω-1m-1; σ increases with temperature

  • Insulator: Does not conduct; σ = 10-8-10-10 Ω-1m-1; ρ = 108-1011 Ωm

Classification Based on Energy Bands

  • Valance Band (VB): Energy band of valence electrons
  • Conduction Band (CB): Energy band of conduction electrons
  • Band Gap Energy (Eg): Energy difference between VB and CB; determines the solid's conductivity type

Types of Semiconductors

  • Intrinsic Semiconductor: Pure semiconductors; e.g., Ge, Si

    • Electrons in CB; Holes in VB
    • Eg for Ge = 0.7 eV; Eg for Si = 1.1 eV

  • Extrinsic Semiconductor: Impure semiconductors; increased conductivity. Two types:

    • N-type: Increased electron concentration; doping with III group elements (e.g., Boron) creates electron-deficient states; major charge carrier: electron (e-)
    • P-type: Increased hole concentration; doping with V group elements(e.g., Phosphorus) creates electron-rich states; major charge carrier: hole (h+)

Materials

  • Elemental Semiconductors: Ge, Si, etc.
  • Compound Semiconductors: CdS, GaAs, CdSe, etc.
  • Organic Semiconductors: Anthracene, doped phthalocyanines
  • Organic Polymers: Polypyrrole, polyaniline, polythiophene, etc.

Applications

  • P-N Junction: Forward bias and reverse bias

    • Forward bias: Electron movement from n-type to p-type; Hole movement from p-type to n-type
    • Reverse bias: Depletion layer widens; current reduced

  • Rectifier (AC to DC): Half-wave, full-wave

    • Half wave rectifier: Converts AC to pulsating DC
    • Full-wave rectifier: Converts AC to smoother DC

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