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#charge carriers

12 public questions tagged with this topic.

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 expecte

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p-n Junction, Depletion Region and Diode Characteristics

The current in a forward-biased p-n junction diode is primarily due to:

**Diode characteristics** forward bias reduces barrier, width of depletion region decreases, resistance low ~10-100 Ω, current primarily due to majority diffusion, exponential I = I_s(e^{eV/kT}-1), reverse bias widens depletion region, resistance high ~MΩ, dominant current drift due to minority carriers, reverse saturation current small μA-nA, typically 10⁻⁶ A, increases sharply at breakdown Zener/avalanche. In forward bias, the applied voltage reduces the barrier height, allowing minority carriers to cross the junction and diffuse, resulting in a current (in mA) due to diffusion of holes and

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p-n Junction, Depletion Region and Diode Characteristics

During p-n junction formation, the depletion region is formed due to:

**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. The depletion region forms due to diffusion of electrons and holes across the junction, leaving behind immobile ionized impurities that create a space-charge regi

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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 behav

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

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p-n Junction, Depletion Region and Diode Characteristics

The barrier potential in a p-n junction opposes the flow of:

**Diode characteristics** forward bias reduces barrier, width of depletion region decreases, resistance low ~10-100 Ω, current primarily due to majority diffusion, exponential I = I_s(e^{eV/kT}-1), reverse bias widens depletion region, resistance high ~MΩ, dominant current drift due to minority carriers, reverse saturation current small μA-nA, typically 10⁻⁶ A, increases sharply at breakdown Zener/avalanche. The barrier potential arises due to the space-charge region and opposes the diffusion of majority carriers (electrons from n-side to p-side and holes from p-side to n-side) at equilibrium.

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, the number of charge carriers increases with:

**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. In an intrinsic semiconductor, thermal energy excites electrons from valence to conduction band, creating electron-hole pairs, and this process increases with rising temperature. Substituting values gives Increase in temperature, which m

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

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Doping, Charge Carriers and Conductivity

In an n-type semiconductor, the number of electrons contributed by donors is:

**Charge carriers** in n-type majority electrons, minority holes, in p-type majority holes, minority electrons, minority concentration reduced due to recombination n_e n_h = n_i², doping increases majority, conductivity σ = e(n_e μ_e + n_h μ_h), increases with doping. Donor ionization energy small ~0.01 eV, electrons easily promoted to conduction band at room temperature. In an n-type semiconductor, each pentavalent donor atom contributes one extra electron, making the electron concentration dependent on doping level, not just intrinsic generation. Substituting values gives Dependent on doping

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

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Semiconductors, Types and Energy Bands

In an intrinsic semiconductor, the equilibrium condition implies:

**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 equilibrium, the rate of generation of electron-hole pairs equals the rate of recombination, maintaining a constant number of carriers ( n_e = n_h = n_i ). Substituting values gives Generation equals recombination, which matches expec

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

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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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Semiconductors, Types and Energy Bands

The electrical conductivity of a semiconductor 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. Semiconductors have intermediate conductivity ( 10⁵ to 10⁻⁶ S m⁻¹ ), between metals ( 10² to 10⁸ S m⁻¹ ) and insulators ( 10⁻¹¹ to 10⁻¹⁹ S m⁻¹ ). Substituting values gives Intermediate to metals and insulators, which matches expected behaviour for this semiconduct

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

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Doping, Charge Carriers and Conductivity

In a p-type semiconductor, the number of holes is related to electrons by:

**Doping** is adding impurity to pure semiconductor to increase carriers, pentavalent (P, As, Sb) donates extra electron, 1 ppm doping in Ge with 4×10²⁸ atoms/m³ gives donor density N_d = 4×10²⁸×10⁻⁶ =4×10²² m⁻³ for 1 ppm, acceptor atoms p-type trivalent B, Al, Ga. Overall charge neutrality maintained because donor ion core positive but electron negative, net neutral. In a p-type semiconductor, trivalent doping increases holes (majority carriers) significantly over electrons (minority carriers), so n_h gg n_e , with n_e n_h = n_i² . Substituting values gives n_h gg n_e, which matches expected

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

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