#semiconductor

Semiconductors, Types and Energy Bands

A germanium diode has a threshold voltage of approximately:

**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. The threshold voltage for a germanium diode, where forward current increases significantly, is approximately 0.2 V, lower than silicon due to its smaller energy gap. Substituting values gives 0.2 V, which matches expected behaviour for t

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p-n Junction, Depletion Region and Diode Characteristics

In a p-n junction, the positive space-charge region is located on:

**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. During junction formation, electrons diffuse from n-side to p-side, leaving behind immobile positive ionized donors on the n-side, forming the positive space-char

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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

The negative space-charge region in a p-n junction is located on:

**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. Holes diffuse from p-side to n-side, leaving behind immobile negative ionized acceptors on the p-side, forming the negative space-charge region of the depletion l

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Rectifiers, Filters and Applications

The diode in a half-wave rectifier conducts during:

**Rectifier applications** diode must have reverse breakdown voltage higher than peak inverse voltage, centre-tap transformer provides two opposite phase voltages for full-wave, capacitor discharges through load R_L when diode off, drift current in junction is minority carrier motion due to field, diffusion due to gradient, diode conducts when forward biased anode positive. In a half-wave rectifier, the diode is forward biased and conducts only during the positive half-cycle of the AC input, blocking the negative half-cycle. Substituting values gives Positive half-cycle, which matches expected

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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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p-n Junction, Depletion Region and Diode Characteristics

In forward bias, the effective barrier height of a p-n junction is:

**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 ( V ) opposes the built-in potential ( V₀ ), reducing the effective barrier height to V₀ - V , allowing more carriers to cross the junction. Substituti

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Semiconductors, Types and Energy Bands

Which of the following has the highest energy gap?

**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. Energy gaps: C (diamond) = 5.4 eV, Si = 1.1 eV, Ge = 0.7 eV, Sn = 0 eV (metal). Carbon has the highest energy gap among these, making it an insulator. Substituting values gives C, which matches expected

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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.

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Doping, Charge Carriers and Conductivity

Which of the following is a trivalent dopant used in p-type semiconductors?

**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. Trivalent dopants (valency 3) like Boron (B), Aluminium (Al), and Indium (In) are used in p-type semiconductors to create holes. Phosphorus (P) is pentavalent. Substituting values gives Aluminium, which matches expected behaviour for this semiconductor device configu

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Semiconductors, Types and Energy Bands

Which of the following is an elemental semiconductor?

**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. Elemental semiconductors are pure elements like Si and Ge, while compound semiconductors (e.g., GaAs, CdS) consist of multiple elements. Among the options, Ge is elemental. Substituting values gives Ge,

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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

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