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5 public questions tagged with this topic.

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,

Ref: NCERT > Physics Book > Electronic Devices > Semiconductors, Types and Energy Bands

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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

Ref: NCERT > Physics Book > Electronic Devices > Semiconductors, Types and Energy Bands

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Doping, Charge Carriers and Conductivity

A Si crystal with \( 5 \times 10^{28} \, \text{atoms} \, \text{m}^{-3} \) is doped with 0.5 ppm of pentavalent impurity.

**Number of carriers** from doping: Ge crystal 4×10²⁸ atoms/m³ doped 2 ppm trivalent gives acceptor atoms 8×10²² m⁻³, holes ≈ that, for 1.5 ppm 6×10²² m⁻³, for 0.5 ppm pentavalent Si 5×10²⁸ atoms/m³ gives 2.5×10²² donors/m³. Acceptor atom effectively negative when accepts electron, donor positive when donates, but crystal neutral. 0.5 ppm = 0.5 × 10⁻⁶ . Number of donor atoms = 0.5 × 10⁻⁶ × 5 × 10²⁸ = 2.5 × 10²² m⁻³ , each contributing one electron. Substituting values gives 2.5 × 10²² m⁻³, which matches expected behaviour for this semiconductor device configuration, confirming doping, depletio

Ref: NCERT > Physics Book > Electronic Devices > Doping, Charge Carriers and Conductivity

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Semiconductors, Types and Energy Bands

Which material has the smallest energy gap among C, Si, and Ge?

**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. The energy gaps are: C (diamond) = 5.4 eV, Si = 1.1 eV, Ge = 0.7 eV. Ge has the smallest energy gap. Substituting values gives Ge, which matches expected behaviour for this semiconductor device configura

Ref: NCERT > Physics Book > Electronic Devices > Semiconductors, Types and Energy Bands

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