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#semiconductor physics

18 public questions tagged with this topic.

p-n Junction, Depletion Region and Diode Characteristics

The thickness of the depletion region in a p-n junction is typically:

**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, formed by diffusion and drift, is very thin, on the order of one-tenth of a micrometer ( 0.1 μ m ), due to the sharp transition at the junct

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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 expecte

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p-n Junction, Depletion Region and Diode Characteristics

The diffusion current in a p-n junction is due to:

**Depletion region** also called space-charge region, thickness typically 0.5 μm, contains no mobile carriers, only fixed ions, negative on p-side, positive on n-side, diffusion current due to concentration gradient, drift current due to field, equilibrium when J_drift + J_diff =0, voltage drop mainly across depletion region. Diffusion current arises from the movement of carriers (holes from p-side to n-side, electrons from n-side to p-side) due to concentration gradients across the junction during its formation. Substituting values gives Concentration gradient, which matches expected behaviou

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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 valu

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 acceptor impurities create:

**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. Trivalent acceptor impurities (e.g., B, Al) in a p-type semiconductor lack one electron per atom, creating holes that act as majority carriers by accepting electrons from the lattice. Substituting values gives Holes, which matche

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p-n Junction, Depletion Region and Diode Characteristics

In a reverse-biased p-n junction, the effective barrier height is:

**Depletion region** also called space-charge region, thickness typically 0.5 μm, contains no mobile carriers, only fixed ions, negative on p-side, positive on n-side, diffusion current due to concentration gradient, drift current due to field, equilibrium when J_drift + J_diff =0, voltage drop mainly across depletion region. In reverse bias, the applied voltage ( V ) adds to the built-in potential ( V₀ ), increasing the effective barrier height to V₀ + V . Substituting values gives V₀ + V, which matches expected behaviour for this semiconductor device configuration, confirming doping, depleti

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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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Doping, Charge Carriers and Conductivity

In an extrinsic semiconductor, the minority carrier concentration is reduced due to:

**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. Doping increases majority carriers (electrons in n-type, holes in p-type), enhancing recombination with minority carriers, thus reducing their concentration indirectly. Substituting values gives Increased recombination, which mat

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Doping, Charge Carriers and Conductivity

The majority carriers in a p-type semiconductor are:

**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 a p-type semiconductor, trivalent doping creates holes as majority carriers, while electrons are minority carriers ( n_h gg n_e ). Substituting values gives Holes, which matches expected behaviour for this semiconductor de

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p-n Junction, Depletion Region and Diode Characteristics

In reverse bias, the width of the depletion region:

**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 reverse bias, the applied voltage increases the barrier height and electric field, widening the depletion region as more immobile charges are exposed due to reduced carrier diffusion. S

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Doping, Charge Carriers and Conductivity

In an n-type semiconductor, the minority carriers are:

**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 an n-type semiconductor, electrons are majority carriers due to pentavalent doping, while holes, generated intrinsically or reduced by recombination, are minority carriers. Substituting values gives Holes, which matches expect

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

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p-n Junction, Depletion Region and Diode Characteristics

The drift current in a p-n junction is caused by:

**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. Drift current results from the electric field in the depletion region, moving electrons from p-side to n-side and holes from n-side to p-side, opposing diffusion at equilibrium. Substituti

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