Semiconductors

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A semiconductor is a material whose electrical conductivity lies between that of conductors and insulators. Conductors like silver have conductivity ~10⁷ S/m, insulators like glass have ~10⁻¹⁰ S/m, wh

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σ = nqμ Where: σ = electrical conductivity (S/m) n = charge carrier density (number of carriers per unit volume) q = charge on the carriers μ = mobility of carriers (ease of movement under electric fi

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For semiconductors: Conductivity INCREASES with temperature because more electrons gain thermal energy (kT) to jump from valence to conduction band. For metals: Conductivity DECREASES with temperature

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Band theory explains electronic properties of solids. When atoms come together: 1. Individual atomic energy levels split due to Pauli exclusion principle 2. Large number of atoms (~10²³) create closel

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METALS: Valence and conduction bands overlap (no band gap). Free electrons easily available for conduction. SEMICONDUCTORS: Small band gap (~1 eV). Electrons can jump to conduction band with thermal o

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An intrinsic semiconductor is a pure semiconductor (like pure Si or Ge) without any impurities. Key features: 1. At absolute zero: all covalent bonds complete, no free carriers 2. At room temperature:

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DOPING: Adding controlled impurities to pure semiconductors to increase conductivity. N-TYPE: Doped with pentavalent atoms (P, As, Sb) - Donors provide free electrons - Majority carriers: electrons,

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Given: 1 ppm = 1/10⁶ Sb atoms = 4×10²⁸/10⁶ = 4×10²² m⁻³ Since each Sb atom donates one electron: nₑ = 4×10²² m⁻³ Using nₑ·nₕ = nᵢ²: nₕ = nᵢ²/nₑ = (1.2×10¹⁶)²/(4×10²²) nₕ = 1.44×10³²/(4×10²²) = 3.6×1