Semiconductors — Important Questions

Doped with pentavalent impurities, Electrons are majority carriers, Donor atoms become positively charged

N-type semiconductors are created by doping with pentavalent impurities (donors) like phosphorus or arsenic. These donate free electrons, making electrons the majority carriers. The donor atoms lose electrons and become positively charged ions.

nₑ = nₕ, Pure semiconductor material, Conductivity increases with temperature, Silicon and germanium are examples

Intrinsic semiconductors are pure materials like silicon and germanium with no impurities. They have equal numbers of electrons and holes (nₑ = nₕ), and their conductivity increases with temperature due to thermal generation of charge carriers.

0.7 V

The knee voltage is the forward bias voltage at which current through the diode starts rising sharply. For silicon diodes, this occurs at approximately 0.7 V, while for germanium diodes it is about 0.3 V.

1.68 S m⁻¹

Step 1: σ = σₑ + σₕ = nₑeμₑ + nₚeμₚ. Step 2: σₑ = 10²⁰ × 1.6×10⁻¹⁹ × 0.1 = 1.6 S m⁻¹. Step 3: σₕ = 10¹⁸ × 1.6×10⁻¹⁹ × 0.05 = 0.08 S m⁻¹. Step 4: Total σ = 1.6 + 0.08 = 1.68 S m⁻¹