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#semiconductor basics

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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, depleti

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

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p-n Junction, Depletion Region and Diode Characteristics

The voltage drop in a forward-biased diode occurs mainly across:

**p-n junction formation** diffusion of holes from p to n and electrons from n to p leaves ionized donors positive on n-side and acceptors negative on p-side, forming space-charge depletion region with electric field directed from n to p (positive to negative), barrier potential V_b ≈0.3 V Ge, 0.7 V Si, opposes further diffusion, drift current due to minority carriers swept by field balances diffusion at equilibrium net current zero. In forward bias, the applied voltage mostly drops across the depletion region due to its high resistance, with negligible drops across the p-side and n-side. Subs

Ref: NCERT > Physics Book > Electronic Devices > p-n Junction, Depletion Region and Diode Characteristics

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Semiconductors, Types and Energy Bands

In an intrinsic semiconductor at \( T > 0 \, \text{K} \), the conduction is due to:

**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. At T > 0 K , thermal energy excites electrons from the valence band to the conduction band, creating electron-hole pairs that contribute to conduction. Substituting values gives Electrons and holes, which matches expected behaviour for t

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

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