Semiconductor Electronics: Materials, Devices and Simple Circuits

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1. **Metals**: Very low resistivity (10⁻² - 10⁻⁸ Ω m), high conductivity (10² - 10⁸ S m⁻¹) 2. **Semiconductors**: Intermediate resistivity (10⁻⁵ - 10⁶ Ω m), intermediate conductivity (10⁵ - 10⁻⁶ S m⁻¹

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**Metals**: Eg ≈ 0 (conduction and valence bands overlap) **Semiconductors**: Eg = 0.2 to 3 eV (small gap allows thermal excitation) **Insulators**: Eg > 3 eV (large gap prevents electron excitation)

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**Intrinsic semiconductor**: Pure semiconductor without any impurities. Charge carriers (electrons and holes) are generated only by thermal excitation. **Key relationship**: ne = nh = ni where: - ne

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**Hole**: A vacancy left behind when an electron breaks free from a covalent bond. It behaves as a positively charged particle with charge +q. **Hole conduction**: When an electron from a neighboring

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**Doping**: Deliberate addition of small amounts (few ppm) of suitable impurities (dopants) to pure semiconductors to increase conductivity. **Necessity**: - Pure semiconductors have very low conduct

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**n-type semiconductor**: Formed by doping Si or Ge with pentavalent impurities (As, Sb, P). **Formation process**: - Pentavalent atom has 5 valence electrons - 4 electrons form covalent bonds with S

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**p-type semiconductor**: Formed by doping Si or Ge with trivalent impurities (B, Al, In). **Formation process**: - Trivalent atom has 3 valence electrons - Forms covalent bonds with only 3 Si neighb

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**Mass Action Law**: ne × nh = ni² This relationship holds for both intrinsic and extrinsic semiconductors in thermal equilibrium. **Significance**: - Product of electron and hole concentrations is