Semiconductors, Types and Energy Bands

Semiconductors, Types and Energy Bands

A germanium diode has a threshold voltage of approximately:

**Semiconductor properties** distinguish from conductors and insulators by temperature dependence and doping response. At 0 K intrinsic acts as insulator, conductivity due to thermally generated electron-hole pairs, number of outer electrons 4 for Si/Ge forming covalent bonds, each atom shares electrons, crystal with N atoms has 4N valence electrons, 2N bonds. The threshold voltage for a germanium diode, where forward current increases significantly, is approximately 0.2 V, lower than silicon due to its smaller energy gap. Substituting values gives 0.2 V, which matches expected behaviour for this semiconductor device configuration, confirming doping, depletion and rectifier principles.

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Semiconductors, Types and Energy Bands

The conductivity of an extrinsic semiconductor increases due to:

**Types of semiconductors** elemental Si, Ge group IV with 4 valence electrons, compound GaAs, InP etc. Intrinsic has n_e = n_h, extrinsic doped with pentavalent donors (P, As) gives n-type excess electrons, trivalent acceptors (B, Al) gives p-type excess holes, resistivity range semiconductors 10⁻⁵ to 10⁶ Ω·m vs insulators 10¹¹ Ω·m. Doping introduces impurities (pentavalent or trivalent) that provide additional charge carriers (electrons or holes), significantly enhancing conductivity compared to intrinsic semiconductors. Substituting values gives Addition of impurities, which matches expected behaviour for this semiconductor device configuration, confirming doping, depletion and rectifier principles.

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Semiconductors, Types and Energy Bands

Which property distinguishes insulators from semiconductors?

**Semiconductor properties** distinguish from conductors and insulators by temperature dependence and doping response. At 0 K intrinsic acts as insulator, conductivity due to thermally generated electron-hole pairs, number of outer electrons 4 for Si/Ge forming covalent bonds, each atom shares electrons, crystal with N atoms has 4N valence electrons, 2N bonds. Insulators have a large energy gap ( E_g > 3 eV ), preventing electron excitation, while semiconductors have a smaller gap ( 0.2 eV to 3 eV ), allowing some conduction. Substituting values gives Energy gap, which matches expected behaviour for this semiconductor device configuration, confirming doping, depletion and rectifier principles.

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Semiconductors, Types and Energy Bands

The number of valence electrons in Si and Ge atoms is:

**Energy bands in semiconductors** consist of valence band filled at 0 K and conduction band empty, gap E_g small ~1 eV (Si 1.1 eV, Ge 0.7 eV), insulators large gap >3 eV (C diamond 5.4 eV), conductors overlapping. Intrinsic semiconductor at 0 K behaves as insulator because no thermal excitation, at T>0 K electrons jump to conduction band leaving holes, conductivity increases with temperature. Si (third orbit) and Ge (fourth orbit) are group IV elements, each with four valence electrons (2s and 2p for Si, 4s and 4p for Ge), forming covalent bonds in their lattice. Substituting values gives 4, which matches expected behaviour for

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Semiconductors, Types and Energy Bands

The primary advantage of a semiconductor diode over a vacuum tube is:

**Types of semiconductors** elemental Si, Ge group IV with 4 valence electrons, compound GaAs, InP etc. Intrinsic has n_e = n_h, extrinsic doped with pentavalent donors (P, As) gives n-type excess electrons, trivalent acceptors (B, Al) gives p-type excess holes, resistivity range semiconductors 10⁻⁵ to 10⁶ Ω·m vs insulators 10¹¹ Ω·m. Semiconductor diodes are small, low-power, operate at low voltages, and have long life and high reliability compared to bulky, high-power vacuum tubes. Substituting values gives Long life and reliability, which matches expected behaviour for this semiconductor device configuration, confirming doping, depletion and rectifier principles.

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Semiconductors, Types and Energy Bands

In an intrinsic semiconductor, the hole movement is due to:

**Energy bands in semiconductors** consist of valence band filled at 0 K and conduction band empty, gap E_g small ~1 eV (Si 1.1 eV, Ge 0.7 eV), insulators large gap >3 eV (C diamond 5.4 eV), conductors overlapping. Intrinsic semiconductor at 0 K behaves as insulator because no thermal excitation, at T>0 K electrons jump to conduction band leaving holes, conductivity increases with temperature. Hole movement is a result of electrons jumping between covalent bonds, creating an apparent motion of the vacancy (hole) in the opposite direction, under an electric field or diffusion. Substituting values gives Electron jumps in bonds, which matches expected behaviour for

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Semiconductors, Types and Energy Bands

In an n-type semiconductor, the donor impurities contribute:

**Semiconductor properties** distinguish from conductors and insulators by temperature dependence and doping response. At 0 K intrinsic acts as insulator, conductivity due to thermally generated electron-hole pairs, number of outer electrons 4 for Si/Ge forming covalent bonds, each atom shares electrons, crystal with N atoms has 4N valence electrons, 2N bonds. Pentavalent donor impurities (e.g., As, P) in an n-type semiconductor donate extra electrons for conduction, significantly increasing the number of free electrons beyond intrinsic levels. Substituting values gives Extra electrons, which matches expected behaviour for this semiconductor device configuration, confirming doping, depletion and rectifier principles.

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Semiconductors, Types and Energy Bands

Which material among Si, Ge, and Sn behaves as a metal?

**Energy bands in semiconductors** consist of valence band filled at 0 K and conduction band empty, gap E_g small ~1 eV (Si 1.1 eV, Ge 0.7 eV), insulators large gap >3 eV (C diamond 5.4 eV), conductors overlapping. Intrinsic semiconductor at 0 K behaves as insulator because no thermal excitation, at T>0 K electrons jump to conduction band leaving holes, conductivity increases with temperature. Sn (tin) has an energy gap of 0 eV, typical of metals with overlapping bands, unlike Si (1.1 eV) and Ge (0.7 eV), which are semiconductors. Substituting values gives Sn, which matches expected behaviour for this semiconductor device configuration, confirming doping, depletion and rectifier principles.

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Semiconductors, Types and Energy Bands

In an intrinsic semiconductor, the total current is the sum of:

**Semiconductor properties** distinguish from conductors and insulators by temperature dependence and doping response. At 0 K intrinsic acts as insulator, conductivity due to thermally generated electron-hole pairs, number of outer electrons 4 for Si/Ge forming covalent bonds, each atom shares electrons, crystal with N atoms has 4N valence electrons, 2N bonds. The total current ( I ) in an intrinsic semiconductor is the sum of electron current ( I_e ) and hole current ( I_h ), i.e., I = I_e + I_h . Substituting values gives Electron and hole currents, which matches expected behaviour for this semiconductor device configuration, confirming doping, depletion and rectifier principles.

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Semiconductors, Types and Energy Bands

In an intrinsic semiconductor, the number of free electrons (\( n_e \)) is equal to:

**Types of semiconductors** elemental Si, Ge group IV with 4 valence electrons, compound GaAs, InP etc. Intrinsic has n_e = n_h, extrinsic doped with pentavalent donors (P, As) gives n-type excess electrons, trivalent acceptors (B, Al) gives p-type excess holes, resistivity range semiconductors 10⁻⁵ to 10⁶ Ω·m vs insulators 10¹¹ Ω·m. In an intrinsic semiconductor, thermal excitation generates equal numbers of free electrons ( n_e ) and holes ( n_h ), so n_e = n_h = n_i , where n_i is the intrinsic carrier concentration. Substituting values gives Number of holes ( n_h ), which matches expected behaviour for this semiconductor device configuration, confirming doping, depletion and rectifier principles.

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Semiconductors, Types and Energy Bands

The resistivity of a semiconductor typically lies in the range:

**Types of semiconductors** elemental Si, Ge group IV with 4 valence electrons, compound GaAs, InP etc. Intrinsic has n_e = n_h, extrinsic doped with pentavalent donors (P, As) gives n-type excess electrons, trivalent acceptors (B, Al) gives p-type excess holes, resistivity range semiconductors 10⁻⁵ to 10⁶ Ω·m vs insulators 10¹¹ Ω·m. Semiconductors have intermediate resistivity between metals and insulators, typically ranging from 10⁻⁵ to 10⁶ Ω m . Substituting values gives 10⁻⁵ to 10⁶ Ω m, which matches expected behaviour for this semiconductor device configuration, confirming doping, depletion and rectifier principles.

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Semiconductors, Types and Energy Bands

What is the primary source of charge carriers in an intrinsic semiconductor at room temperature?

**Types of semiconductors** elemental Si, Ge group IV with 4 valence electrons, compound GaAs, InP etc. Intrinsic has n_e = n_h, extrinsic doped with pentavalent donors (P, As) gives n-type excess electrons, trivalent acceptors (B, Al) gives p-type excess holes, resistivity range semiconductors 10⁻⁵ to 10⁶ Ω·m vs insulators 10¹¹ Ω·m. In an intrinsic semiconductor, charge carriers (electrons and holes) are generated by thermal excitation at temperatures above 0 K, breaking covalent bonds and creating electron-hole pairs. Substituting values gives Thermal excitation, which matches expected behaviour for this semiconductor device configuration, confirming doping, depletion and rectifier principles.

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